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14 Survey methodology 14.1 Overview of the survey design The 1999 Health Survey for England was designed to provide data at both national and regional level about the population aged 2 and over living in private households in England, with special emphasis on the health of the most populous minority ethnic groups: Black Caribbean, Indian, Pakistani, Bangladeshi, Irish and Chinese.1 As in previous years, the sample for the 1999 survey included a cross-section of the population for which over 6,500 addresses were drawn from the Postcode Address File (PAF). The general population sample was set at about half the size of those in most previous years of the Health Survey, so that resources could be devoted to boosting the numbers of minority ethnic group members. To achieve this, a minority ethnic boost sample was designed, involving the selection of over 64,000 additional addresses, using the complex sample design described below (Section 14.2). The sample of Chinese men and women, however, was boosted by a different method, namely re-contacting addresses involved in a previous survey of the health of the Chinese population. As in previous years, all persons aged 2 and over were eligible for inclusion in the survey. At addresses where there were more than a specified number of children (n) aged 2-15, n children were selected at random. For the general population, n was set at 2, as in earlier years. For the minority ethnic group boost sample, n was set at 3. The 1999 survey also set a limit of 4 on the number of adults aged 16 and over who could be interviewed in any one household in the minority ethnic boost sample. No such limit had been set for the general population sample in this or in earlier years of the Health Survey. Information was obtained directly from persons aged 13 and over. Information about children aged 2-12 was obtained from a parent, with the child present. For both adults and children, the data collected differed between the general population sample and the minority ethnic boost sample. For all informants, there was a computer-assisted interview by an interviewer with each eligible person (Stage 1). The interview with minority ethnic group members, whether in the boost sample or found in the general population sample, was longer than for the remainder of the general population sample. Minority ethnic group members were also visited by a nurse (Stage 2) who made a number of measurements and obtained a sample of saliva from those aged 4 and over and a sample of blood from those aged 11 and over.2 Nurses also used computer-assisted interviewing. Blood and saliva samples were sent to a laboratory for analysis. Interviewing was conducted throughout the year to take account of seasonal differences. 14.2.1 Summary of the sample design in the Health Survey series The surveys in the Health Survey series have all adopted a similar multi-stage stratified probability sampling design. The population surveyed has been the population living in private households. Those living in institutions have not been covered.3 They are likely to be older and, on average, in poorer health than those in private households, and this should be borne in mind when considering the Health Survey's account of the population's health. The sampling frame has been the small user Postcode Address File (PAF). The very small proportion of households living at addresses not on PAF (less than 1%) have not been covered. Postcode sectors have been the primary sampling units (PSUs).4 In 1995 children were introduced into the Health Survey for the first time. This change was accommodated within the same sample design by reducing the lower age limit of eligibility within each household from 16 to 2. Children have been included in all subsequent years. 14.2.2 Sample design for the 1999 Health Survey The 1999 Health Survey included three independently designed samples. The first was for the general population sample, which was designed to be representative of the whole population living in private households in England. It involved selecting 6,552 addresses throughout England using the small user Postcode Address File (PAF). As in previous years, the design was two-stage, involving the selection of postal sectors, within which addresses were selected. The second sample, the minority ethnic boost sample, also two-stage, involved selecting 26,528 addresses. These were all 'screened' in order to determine if they contained residents from the relevant minority ethnic groups, using a combination of full screening and focused enumeration (see Section 14.2.5). These addresses were not eligible for the survey unless they contained at least one resident from the following minority ethnic groups: Black Caribbean, Indian, Pakistani, Bangladeshi or Irish. Addresses for the sample for boosting minority ethnic groups were selected completely independently from the general population sample. The third sample was that for Chinese informants, which involved re-contacting addresses at which households had participated in an earlier survey of health-related behaviour and beliefs in the Chinese community.5 The sample design for the 1999 Health Survey is described more fully below. Sections 14.2.3 and 14.2.4 describe the general population sample design. Sections 14.2.5 to 14.2.7 describe the sample design for boosting minority ethnic informants, except for the Chinese which is described in Section 14.2.8. 14.2.3 Selection of primary sampling units (PSUs) for the general population sample For the general population sample, 312 postcode sectors were selected as PSUs. Before selection, postal sectors were stratified in order to maximise the precision of the sample. Postal sectors with fewer than 1,000 PAF 'delivery points' were first combined with neighbouring sectors so as to avoid any tight clustering of sampled addresses. Two stratification levels were used. Postal sectors were first sorted by Health Authority (ensuring correct Health Authority and regional balance) and then, within Health Authority, were listed in order of the percentage of households with a head of household in a non-manual occupation (Socio-Economic Groups 1-6,13). The data used to classify postal sectors by the proportion of household heads in non-manual occupations was taken from the 1991 Census of Population. 312 sectors were then selected systematically, with each postcode sector being given a probability of selection proportional to its total number of 'delivery points' (addresses). After selection, each sector was randomly divided into two equal halves (in terms of number of delivery points) and one of the two halves was selected at random to become the PSU. By selecting sectors with probability proportional to the number of addresses, and then selecting a fixed number of addresses within each, every address is given an equal chance of inclusion, even when confined to a random half of the sector. Once selected, the PSUs were randomly allocated to a month of the year, with an equal number of PSUs being assigned to each month. This was done so that fieldwork conducted in each quarter of the year was carried out with a fully representative sub-set of the total sample. 14.2.4 Sampling delivery points (addresses) for the general population sample 21 delivery points (addresses) were systematically selected from each PSU, giving a total selected sample of 6,552 addresses. When visited by interviewers, 10% of the selected addresses were found to contain no private households. Examples include businesses and institutions, vacant properties, demolished addresses and those still in the process of being built. These addresses were then ineligible and were excluded from the survey sample. A small proportion of addresses on PAF contain more than one household. Interviewers were instructed to include in the sample all households at addresses with one, two or three households. In the rare event of an address containing more than three households, the interviewer was given a special procedure to follow, using random selection digits provided. This procedure resulted in a random selection of three households from among all households at an address. The three selected households were included in the survey sample, and the others were omitted. In principle, the sample should be weighted to take account of the omitted households. In practice, because there are so few cases, the complications introduced by this weighting would not be justified. At each selected general population sample address, all resident adults (aged 16 and over) were eligible for inclusion in the survey. Children aged 2-15 were also eligible for inclusion. However, in order to limit the burden on households with three or more children in this age range, two were randomly selected for the survey. No interviews were attempted with the other children. As 15% of contacted households containing children aged 2-15 had three or more children in this age group, 11% of all children were omitted from the sample. The application of weights is required to compensate for these omissions (see Section 14.8), otherwise children from large households would be under-represented. 14.2.5 Selection of primary sampling units for the minority ethnic boost sample For the independently selected sample for boosting minority ethnic groups, an additional 408 postcode sectors were selected as the primary sampling units. As for the general population sample, postal sectors with fewer than 1,000 PAF delivery points were combined with adjacent sectors to avoid too tight a clustering of sampled addresses. Before this stage of selection, all postcode sectors in England were assigned to one of eight strata (A to H) based on the proportion of residents (using data from the 1991 Census of Population) in the sector who were Black Caribbean, Indian, Pakistani, Bangladeshi or, for stratum G, Irish. The eight strata were defined as follows: Stratum:
In Stratum G, only residents of Irish origin were eligible for inclusion in the sample. The number of postcode sectors selected for the boost sample varied by stratum. Stratum H was not sampled. Within strata A-G, postcode sectors were selected systematically, with each sector being given a probability of selection proportional to its total number of delivery points. The number of sectors selected from each stratum are shown in column (b) below:
As in the general population sample, the 408 postcode sectors for the boost sample were randomly allocated to a month of the year, with 34 sectors to be covered each month. However, as fieldwork progressed, it became clear that the number of interviews achieved with informants from the relevant minority ethnic groups was going to considerably surpass the original target. As a result, it was decided to issue only 10 of the planned 12 months of the sample, so the 68 postcode sectors which were due to be covered in the final two months of fieldwork were, in the event, not issued to interviewers. Column c) in the above table shows the number of sectors issued within each stratum. In postcode sectors allocated to strata A, B, C, D and G, a full screening operation was carried out. Interviewers were issued with a sample of addresses and required to contact each address to determine whether there were any residents eligible for inclusion in the survey. In sectors in strata E and F, which have a much lower density of residents from minority ethnic groups, the screening technique of 'focused enumeration' was used. In areas where there are relatively few minority ethnic residents, this technique provides a cost effective way of screening a large number of addresses. Focused enumeration makes use of local knowledge by asking neighbours to identify members of minority ethnic groups living at adjacent addresses. For the Health Survey, interviewers working in postcode sectors from strata E and F were issued with a sample of addresses, and they screened for eligibility at the sampled address as well as determining (by asking at the sampled address) whether any eligible persons lived at the two addresses either side of the sampled address. Thus, up to five addresses are covered by each sampled address. If any of the adjacent addresses was thought to include residents of the relevant minority ethnic groups (or was unsure), the interviewer made a personal visit to the relevant address to carry out the screening interview. As focused enumeration is more likely to work for people of Black and Asian origin, this technique was not used to identify people of Irish origin. In strata E and F, Irish residents were determined only at the sampled address and not at adjacent addresses. In theory, this procedure (of covering two addresses on either side) should increase the number of eligible informants by a factor of five, but in practice the increase is lower for several reasons: although the technique has been shown to work well, there is inevitably some under-enumeration of the relevant minority ethnic groups; in some cases, there are no adjacent addresses; and response tends to be lower at the adjacent addresses than at the main address. The sample design aimed to obtain a minimum number of informants within each ethnic group, while keeping the total number of informants per group approximately the same. In order to achieve this, the higher prevalence groups, Indian and Irish, were not screened in a proportion of sample points in the higher density strata, and the smallest group, Bangladeshi, was boosted with an additional sample of points in which only people of Bangladeshi origin were eligible for interview. For screening purposes, the sampled sectors were grouped into six 'sample types' which determined for each sector both the minority ethnic groups that were being screened and the method of selecting addresses. The six sample types were:
For sample types 1, 2, 3, 5 and 6, each postcode sector was divided into two equal parts (in terms of number of delivery points) and one of the two halves was selected at random for inclusion in the sample. If a particular postcode sector was selected for both the general population and the boost samples, half of the sector was randomly allocated to the general population sample, and the other half to the boost sample. 15 of these sample type sectors were in both the general population and minority ethnic boost samples. In sample type 4, however, the whole postcode sector was included in the sample, except for the 11 sectors in sample type 4 which were also part of the general population sample; in these cases, half the sector was allocated to the general population sample and the other half to the boost sample. 14.2.6 Sampling delivery points (addresses) for the minority ethnic boost sample The number of addresses selected for each sample type, and the total number of issued sectors per type were:
This gave a total of 26,528 sampled addresses. All the sampled addresses were fully screened, and a further 37,632 adjacent addresses were covered by focused enumeration. This resulted in a total of 64,160 addresses covered by the screening exercise. As in the general population sample, at addresses with more than one household, all households up to a maximum of three were included; if there were more than three households, the interviewer randomly selected three for inclusion in the sample. 14.2.7 Sampling individuals within addresses for the minority ethnic boost sample Because minority ethnic groups tend to live in larger than average households it was decided to sub-select for interview a maximum of 4 adults (ages 16 and over) and 3 children (ages 2-15) in order to limit the potential burden on households in the minority ethnic boost sample. No interviews were attempted with the other adults or children who had not been selected. The application of weights is required to compensate for this sub-selection of adults and children (see Section 14.8). 14.2.8 Sample design for Chinese informants Because Chinese residents are a very small proportion of the population in England and are dispersed throughout the country, obtaining a probability sample can be very costly. For this reason, the sample of Chinese informants was not selected independently for the Health Survey; rather, it was obtained by following up addresses with Chinese residents identified in a survey the National Centre carried out on behalf of the Health Education Authority (HEA, now the Health Development Agency) in 1998, which looked at the health and lifestyles of Chinese residents aged 16-74 in England. Full details of the survey results and methodology may be found in Health and Lifestyles of the Chinese Population in England.5 Sampling for the 1998 Chinese survey The sampling methodology for the 1998 HEA survey was based on procedures devised by the Office for National Statistics (ONS) specifically for sampling Chinese residents. Firstly, it was decided to include only those areas identified in the 1991 Census as having the highest proportions of Chinese residents, which included: Greater London; the rest of the South East region; Greater Manchester; Merseyside; South Yorkshire; West Midlands; and West Yorkshire. There were two stages of selection. All the wards in these areas were grouped into six strata according to the density of the adult Chinese population, and the wards were then randomly selected, with the selection probabilities varying by strata. The strata and number of wards selected in each were:
At the next stage, within each selected ward, people were sampled from the Electoral Register using the most common (about 1,300) Chinese surnames. This was done by compiling a list of all addresses on the Electoral Register which had residents with 'Chinese-sounding' surnames (and ensuring that each address was only listed once). These addresses comprised the sampling frame of (potential) Chinese people. In the highest density stratum (Stratum A), 20% of these addresses were randomly selected; in Stratum B, 50% of such addresses were selected; and in Strata C-F, all such addresses were selected. This method yielded 3,858 addresses containing individuals with 'Chinese-sounding' names which were issued to interviewers. A maximum of three households at an address were eligible for inclusion in the survey, and three were randomly selected in the rare case of there being more than three. At each address, interviewers established the number of people of 'Chinese origin' (the definition of which was left to an adult member of the household) aged 16-74 at each address. All adults in this age group, up to a maximum of 3, were eligible for interview. In all, 1,022 people in 643 co-operating households were interviewed for the 1998 HEA survey. 569 (88%) of these co-operating households had agreed (as part of the HEA interview) to be followed-up in subsequent interviewing, and were thus eligible for inclusion in the 1999 Health Survey Chinese boost sample. Utilising the 1998 Chinese survey sample in 1999 The addresses containing the 569 households defined above were issued to Health Survey interviewers.7 They were effectively treated as a new sample of households with potential Chinese informants, rather than as a follow-up interview with the same persons as in the 1998 HEA survey. No data from the HEA survey was utilised. At each address the interviewer established the number of Chinese residents aged 16 and over in order to select a maximum of 4 of these adults at random for inclusion in the sample (whether or not they were interviewed in the 1998 HEA survey); similarly, a maximum of 3 children aged 2-15 were randomly selected for the Health Survey. No attempt was made to follow-up informants to the HEA survey who had subsequently moved to a new address. 14.2.9 Minority ethnic groups in the general population sample In addition to those identified in the boost sample, a number of informants from the eligible minority ethnic groups were identified in the general population sample. To obtain the total minority ethnic group sample that is reported here, informants from eligible groups who were identified in the general population sample were included with those from the boost sample. As explained above, postcode sectors in Stratum H were excluded from the minority ethnic boost sample, and in Stratum G only Irish informants were sampled. All of these sample points were however included in the general population sample, so that the combined sample of informants (from both the general population sample and the boost sample) could be weighted to be fully representative of the minority ethnic population in England. In practice, however, to gain full representation the weights applied to Black Caribbean and South Asian informants from Strata G and H, and to the Irish from Stratum H, would have to be very large relative to minority ethnic informants from other strata. Since having a large variation in the weights would make the survey estimates unstable, the weights for the small number of minority ethnic informants from these strata have been trimmed. This means that Black Caribbean and South Asian minority ethnic groups living in Strata G and H are slightly under-represented in the minority ethnic sample, as are the Irish from Stratum H. To summarise, minority ethnic informants identified in the general population sample are included in both the general population sample and the minority ethnic sample in this report, but minority ethnic informants living in areas with very low proportions of minority ethnic residents are marginally under-represented in the latter sample. 14.3.1 Documentation Copies of all the survey data collection documents are included in Appendix A. Measurement and saliva and blood sample collection protocols are given in Appendix B. The content of the Stage 1 interview and the Stage 2 nurse visit is summarised below. 14.3.2 Coverage of the Stage 1 interview The coverage of the interview was different for minority ethnic group members and the remainder of the sample, the former being given the full, and the latter a short, version of the questionnaire. This section focuses on the content of the full interview. Data was collected at two levels: household and individual. Figure
14A summarises the content of the household and individual level interviews
for all informants: topics indicated with an The interview with informants from the general population sample included the question modules which are asked in most years of the Health Survey, such as general health and longstanding illness, use of health services, cigarette smoking, psycho-social health (GHQ12), physical activity and accidents. Also included in the 1999 survey were questions on ethnic origin, country of birth, religion and cultural identity. Informants from the minority ethnic groups were asked these question modules as well as several others including a module on cardiovascular disease (CVD) for adults, and a module on asthma for children. The questions on CVD were based on those used in 1993, 1994 and 1998. The asthma questions were developed for inclusion in 1995, and were also used in 1996 and 1997. Questions on the use of health services, physical activity, smoking, alcohol consumption, accidents and general health were the same as those used in 1998. Figure 14a Topics covered in the 1999 Health Survey for England Household level data
a These modules were administered by self-completion for those aged16-17 and some aged 18-24. b These modules were administered by self-completion. Informants aged 8 and over were asked to complete a self-completion booklet during the interview. There were four booklets: one for adults, one for young adults aged 16-17, one for teenagers aged 13-15, and one for children aged 8-12. The information obtained in this way is shown below. Adults booklet GHQ12, social support, contraceptive pill and HRT use.
14.3.3 Coverage of the Stage 2 nurse visit The following types of informant were eligible for a nurse visit: all those in the minority ethnic boost sample; informants in the Chinese boost sample; informants from five (of the six) relevant minority ethnic groups in the general population sample (Chinese informants in the general population sample did not have a nurse visit).2 Nurses collected information about use of prescribed medicines, vitamin or mineral supplements and nicotine replacement products. They took blood pressure, lung function, electrocardiogram, waist, hip, mid-upper arm circumference and demi-span measurements. Each measurement was limited to a particular age range as shown in Figure 14A. A saliva sample for cotinine assay was obtained from those aged 4 and over. During the nurse visit, informants aged 16 and over were also given a self-completion questionnaire about their eating habits. Parents of children aged 4-15 were given a self-completion booklet about each child aged 4-15 sampled for the survey. This booklet included the Strengths and Difficulties Questionnaire (SDQ) which is designed to detect possible emotional, behavioural or relationship problems among children of this age. 14.3.4 Collecting blood samples Nurses also requested a small sample of blood by venepuncture from those aged 11 and over and obtained appropriate consents. The protocols for obtaining blood from informants aged 11-17 (minors) were changed for the 1998 Health Survey after consultation with the Royal College of Paediatrics and Child Health and involve offering them the option of using an anaesthetic cream. These samples were analysed for: total cholesterol, HDL-cholesterol, haemoglobin and ferritin for informants aged 11 and over; fibrinogen, glycated haemoglobin and C-reactive protein for those aged 16 and over; and for ages 11-15 only, IgE and house dust mite IgE. Informants aged 35 and over were also asked to provide a fasting blood sample which was analysed for triglycerides, LDL cholesterol and glucose. Nurses also sought agreement for the storage of a small sample of blood for possible future analysis. 14.3.5 Defining age for data collection and other purposes A considerable part of the data collected in the 1999 Health Survey is age specific, with different questions directed to different age groups. The informant's date of birth was ascertained. For data collection purposes, an informant's age was defined as their age on their last birthday before the interview. The nurse, who visited them later, treated them as being of the same age as at the interview, even if they had an intervening birthday. Age is a continuous variable, and an exact age variable on the data file expresses it as such (so that, for example, someone whose 14th birthday was on January 1 1999 and was interviewed on October 1 1999 would be classified as being aged 14.75 (143/4)). The presentation of tabular data involves classifying the sample into year bands. There are two main ways of doing this:
Rounded age was used for certain analyses of children in the 1995 and 1996 Health Survey reports, but in the present report all references to age are to age at last birthday. 14.3.6 Provision for non-English speaking informants All survey materials and questionnaires were translated into seven languages: Hindi, Gujarati, Punjabi, Urdu, Bengali, Mandarin and Cantonese. Interviewers who could speak and read these languages (as well as English) were recruited and trained in the survey procedures. Other people in a household were never used as interpreters, at either Stage 1 or Stage 2, for informants who could not speak English sufficiently well to be interviewed in English. The procedure was to allocate an interviewer who could speak the appropriate language to a non-English speaking informant so that the interview could be conducted in the informant's own language. The same interviewer also accompanied the nurse for the Stage 2 visit. Ethical approval for the 1999 survey was obtained from the North Thames Multi-Centre Research Ethics Committee and from all Local Research Ethics Committees (LRECs) in England. 14.5.1 Advance letters Every sampled address, in both the general population and boost samples (except addresses screened using the focused enumeration procedure), was sent an advance letter which introduced the survey and stated that an interviewer would be calling to seek permission to interview. 14.5.2 Making contact At initial contact, the interviewer established the number of households living at an address. If there were three or fewer, all were included in the sample. If there were more than three, three were selected for inclusion in the survey, using a random selection procedure. For the general population sample, the interviewer then made contact with each household and attempted to interview all adults and up to 2 eligible children (see below). For the boost sample (including the separate Chinese sample), the interviewer made contact with a household and asked the appropriate screening questions. The screening questions varied according to the sample type, as this determined which minority ethnic groups were being screened for at a particular address (as described in Section 14.2.5). A household was screened in if it contained at least one member from any of the minority ethnic groups being screened for (within that sample type). At screened-in addresses, the interviewer attempted to interview up to 4 eligible adults and 3 eligible children (see below). If a household contained no members of the relevant minority ethnic groups, then it was screened out of the sample and no interviews were attempted. At addresses in sample type 4 (see Section 14.2.5), the screening questions were also asked about the two adjacent addresses either side of the sampled address. Because focused enumeration relies on 'visual' identification, it was used only to identify the possible presence of people of Black Caribbean or South Asian origin. If the person at the sampled address was certain that there were no residents of Black Caribbean or South Asian origin at a neighbouring address, that address was screened out of the sample. The interviewer attempted to make contact at any adjacent addresses where the person at the sampled address either knew (or thought) there was someone of Black Caribbean or South Asian origin, or did not know if there were any such residents, or refused to answer the screening questions about the neighbouring addresses. At each adjacent address the appropriate screening questions were asked and, if a household was screened in at that stage, interviews with up to 4 eligible adults and 3 eligible children were attempted. 14.5.3 Collecting data At each co-operating eligible household, the interviewer first completed a Household Questionnaire, information being obtained from the head of household or their partner wherever possible. This questionnaire obtained information about all members of the household, regardless of ethnicity or age. In the general population sample, all adults aged 16 and over were eligible for the Individual Questionnaire. If there were 1 or 2 children aged 2-15, they were automatically included in the sample for further interview. If there were 3 or more children aged 2-15, the computer program used random numbers to select 2 for interview. Individual Questionnaires were created by the program for these 2 children only. In the minority ethnic boost sample, a maximum of 4 adults aged 16 and over and 3 children aged 2-15 were eligible for interview within each household. Eligibility for interview, for adults and children, was determined during completion of the Household Questionnaire. The head of household (or their partner) was asked the ethnic group of all household members; all those thus classified in one of the relevant minority ethnic groups were eligible for interview (see below). In households with more than 4 eligible adults and/or 3 eligible children, the computer program used random numbers to select 4 adults/3 children for interview, and Individual Questionnaires were created by the program for the selected individuals. Eligibility for the boost sample included people from the following minority ethnic groups: Black Caribbean; Indian; Pakistani; Bangladeshi; Chinese; and Irish. For the Black Caribbean, South Asian and Chinese groups, eligibility was self-assessed in that informants were asked whether they considered they belonged to any of the relevant minority ethnic groups. The criterion for inclusion in the Irish boost sample was having been born in Ireland (either Northern Ireland or the Republic of Ireland) or having a parent born in Ireland. An Individual Questionnaire interview was carried out with all sampled adults and children. As explained in Section 14.3.2, the interview varied depending on whether informants were part of the general population or boost samples, although informants from the relevant minority ethnic groups in the general population sample were given the same version of the Individual Questionnaire as informants in the boost sample. As in earlier Health Surveys, in order to reduce the amount of time spent in a household, interviewers were permitted to carry out several interviews concurrently, the program allowing for up to 4 informants to be interviewed in a session. Height and weight measurements were obtained towards the end of the interview. At the end of the interview, informants who were eligible for a nurse visit (see Section 14.3.3) were asked for their agreement to the second stage of the survey, the follow-up visit by a nurse. In the case of children aged 2-15, it was the parent's permission that was sought (see Section 14.5.6). Wherever possible an appointment was made for the nurse to visit within a few days of the interview. For informants who did not speak English, the nurse was accompanied by an interviewer who spoke the appropriate language. At this visit the nurse carried out the measurements described in Section 14.3.3 and obtained the saliva and blood samples. Before a blood sample was taken, written consent was obtained from the informant. If the informant was aged 11-17, the additional written consent of a parent or guardian (with legal parental responsibility) was required. Nurses also asked informants for consent to store part of the blood sample for additional analyses at some future date. If the informant agreed, written consent was obtained. (All consent forms were translated into seven languages - see Section 14.3.6.) All informants aged 11-17 who consented to give a blood sample were given the option of having an anaesthetic cream applied beforehand. Those requesting the use of anaesthetic cream had to wait at least 60 minutes after application for venepuncture to take place. In addition to an advance letter, informants were given two leaflets describing the purpose of the survey and of the associated measurements. Interviewers handed out one describing the purpose of the interview, and nurses handed out one explaining the purpose of their visit. (The leaflets were translated into seven languages - see Section 14.3.6.) Copies of the (English versions) of these two documents are appended. Informants were also given a leaflet summarising some findings from previous surveys. 14.5.4 Feedback to informants Each informant was given a Measurement Record Card in which the interviewer entered the informant's height and weight and (when relevant) the nurse entered waist, hip, upper arm circumference, demi-span, blood pressure and lung function measurements. Informants were also sent (if they wished) the results of their blood sample analyses. Informants who saw a nurse were asked if they would like their blood pressure and ECG readings, and blood sample analyses, sent to their GP. If they did want results to go to their GP, written consent was obtained. Nurses were issued with a set of guidelines to follow when commenting on informants' blood pressure readings (see Appendix B for details). In summary, if an adult's blood pressure reading was severely raised, nurses were instructed to contact the Survey Doctor at the earliest opportunity. They were instructed not to comment on a child's reading but to leave the Survey Doctor to assess whether any action was required. Where permission had been given for results to be sent to an informant's GP, the Survey Doctor contacted the GP if any blood pressure, ECG or blood sample results were abnormal. 14.5.5 Quality control measures Training interviewers and nurses Interviewers were fully briefed on the administration of the survey, including screening for eligible informants in the boost sample. They were given training in measuring height and weight (including a practice session). All nurses were professionally qualified and proficient in taking blood before joining the Health Survey team. They attended a two-day training session at which they received equipment training and were briefed on the specific requirements of the survey with respect to taking blood pressure, making anthropometric and ECG measurements and taking saliva and blood samples. Full sets of written instructions, covering both survey procedures and measurement protocols, were provided for both interviewers and nurses (Appendix B contains a copy of the measurement protocols). Interviewers and nurses who had worked on the previous year's survey attended full day refresher training sessions, whose emphasis was on improving measurement skills and gaining informant co-operation. It also included training in taking ECG measurements, as this was the first year this equipment was used in the Health Survey. All interviewers and nurses new to the Health Survey were accompanied by an interviewer or a nurse supervisor during the early stages of their work to ensure that interviews and protocols were being correctly administered. Routine supervision of the work of both interviewers and nurses was carried out thereafter. Checking interviewer and measurement quality A large number of quality control measures were built into the survey at both data collection and subsequent stages to check on the quality of interviewer and nurse performance. Recalls to check on the work of both interviewers and nurses were carried out at 10% of productive households. The computer program used by interviewers had in-built soft and hard checks, which included messages querying uncommon or unlikely answers. For example, if someone aged 16 or over had a height entered in excess of 1.93 metres, a message asked the interviewer to confirm that this was a correct entry. For children, the checks were age specific. At the end of each survey month, the measurements made by each interviewer and nurse were inspected. For example, if a nurse had obtained a number of abnormally low lung function measurements, this could be an indication of inadequate instructions to informants on how to perform the test. Supervisors discussed such results with the relevant nurse or interviewer. 14.5.6 Interviewing and measuring children Children aged 13-15 were interviewed directly by interviewers, permission having first been obtained from the child's parent or guardian. Interviewers were instructed to ensure that the child's parent or guardian was present in the home throughout the interview. Information about younger children was collected from a parent. Younger children were present while their parent answered questions about their health. This was partly because the interviewer had to measure their height and weight and, in the case of those aged 8 and over, to ask the child to complete a short self-completion booklet during the interview. It also ensured that the child could contribute information. Permission for a nurse to carry out any measurements on a child aged 2-15 had to be obtained from the child's parent or someone else with legal parental responsibility for that child. This person had to be present during the nurse visit. In 4 households there was a child for whom no-one accepted such responsibility, and no nurse visit was therefore arranged. Written consent to send information to a child's GP was obtained from the parent. 14.6.1 Response analysis The sample design, described in Section 14.2, for the general population sample required all adults and up to 2 children aged 2-15 to be interviewed. For the minority ethnic boost sample, a maximum of 4 adults and 3 children aged 2-15 were interviewed within any one household. Non-respondents to the survey, for both sample types, fall into two groups, those living in households where no-one co-operated with the survey and those living in households where at least one person was interviewed. This section looks at response, of sampled households and then of eligible individuals within those households, firstly for the general population sample (Sections 14.6.2 - 14.6.5) and then for the minority ethnic boost sample (Sections 14.6.6 - 14.6.8). It also looks at variations in response by minority ethnic group. Individual response for adults and children is looked at in two ways: overall response by all (estimated) eligible individuals and response by individuals within co-operating households. In the minority ethnic boost sample, because informants were asked to co-operate in a sequence of operations, beginning with a face-to-face interview, progressing to a nurse visit and ending with a request for saliva and blood samples, individual non-response accumulated through the survey stages. Not every measurement obtained by an interviewer or a nurse was subsequently considered valid for analysis purposes. For example, informants who reported eating, drinking or smoking in the 30 minutes prior to the blood pressure measurement were excluded from analysis, as were those for whom fewer than three blood pressure readings were obtained (the average of the last two readings forming the basis of analyses). Full details of the numbers of measurements used for analysis, the number of exclusions and the reasons for them are given in the relevant chapters. 14.6.2 General population sample: household response Table 14.1 shows the household response for the general population sample by region. The row labelled 'Total eligible households' shows the number of private residential households found at these addresses (after selection of 3 households if more than 3 were found). Households described as 'co-operating' are those where at least one eligible person was interviewed at Stage 1. Households described as 'all interviewed' are those where all eligible persons were interviewed. 76% of eligible households (4,551) in the general population sample took part in the 1999 Health Survey. At 67% of households in the general population sample, all eligible adults and children were interviewed. 14.6.3 General population sample: individual response - adults Overall response There were 7,798 individual interviews with adults. The numerator of the response rate - the number of productive outcomes - is of course known (though as already noted, there are a variety of different outcomes). The denominator - the total number of adults in the sampled households - is not known and must be estimated. There are two groups of households to consider: productive households where a household questionnaire has been completed (nearly all co-operating households, although this category also includes a few households where there was only a household questionnaire and no individual interviews) and the number of adults is known (8,469 adults in 4,561 households, average 1.86), and unproductive households about which nothing is known (1,414 households). The total number of adults in all sampled households is estimated by assuming that the unproductive households have the same characteristics, on average, as the productive households (eg, the same average household size, the same proportion of men and women). Applying the appropriate weight to the productive households gives an estimated total of 11,095 adults (the 'set' sample) of whom 5,254 are men and 5,840 are women. Evidence suggests that unproductive households tend to be smaller on average than productive households, so this estimate of the total number of eligible adults is likely to be too large, and response rates based on it will be underestimated. Using this estimate as a denominator, minimum response rates for adults in the general population sample were:
Response to the interview was 73% among women and 68% among men. (Informants from the minority ethnic groups within the general population sample were eligible for later stages of the survey; response rates to these stages are shown along with those for all minority ethnic informants in Section 14.6.7.) Adult response in co-operating households As adults' ages and other personal characteristics are not known in the unproductive households, indications of response differences by these characteristics are confined to co-operating households. Table 14.5 shows the proportion of men and women, by age, in co-operating households from the general population sample who participated in the interview stage of the survey. In co-operating households, response was highest among those aged 65 and over (97% of men and women) and lowest among those aged under 25 (85% of men and 87% of women). 14.6.4 General population sample: individual response - children Overall response Interviews were carried out with 1,842 children in the general population sample (in the case of those aged 2-12 the information was obtained from a parent). To compute the response rate the number of eligible children in sampled households (the 'set' sample) is needed as the denominator. As described in Section 14.6.3, this was estimated by assuming that unproductive households have the same characteristics on average as the productive households (eg, the proportion of unproductive households containing 0, 1, 2...children aged 2-15 is the same as among contacted households). This results in a 'set' sample of 2,498 children. This is likely to be an over-estimate, since non-contacted households probably have fewer children, on average, than those contacted. Response rates computed for children, like those for adults, are therefore probably conservative. Almost all non-responding children were in households where no-one (child or adult) co-operated with the survey. Among the 'set' sample of 2,498 children, response rates were:
There were no differences in response rates between boys and girls. Child response in co-operating households Child response rates, like adult response rates, have been calculated on a co-operating household base. The proportion interviewed was high overall, at 97% for both boys and girls. 14.6.5 Variation in survey response Regional variations in response As in previous years, response varied by region (NHS Regional Offices). Household response was highest in the Trent and Northern & Yorkshire regions and was lowest in the North Thames and South Thames regions. Response by type of dwelling Table 14.2 shows household response by the type of building housing the address (as classified by interviewers). Response was highest among households living in detached or semi-detached houses (80%) and lowest among households living in converted flats (62%). 14.6.6 Boost sample: household response As described in Section 14.2.5, the minority ethnic boost sample consisted of six 'sample types', which varied either by the minority ethnic groups being screened or by the screening method employed (ie, full screen or focused enumeration). Table 14.7 shows the household response rate by these six sample types. The row labelled 'Screened in' shows the number of known eligible households within each sample type. At least one minority ethnic informant was interviewed at 71% of known eligible households within the boost sample. At 59% of known eligible households, all selected adults and children were interviewed. The household response rate to the first stage interview was similar for sample types 1 to 4, but was considerably higher for sample types 5 (86%) and 6 (80%), which were screening for people of Bangladeshi and Irish origins respectively. Some of the addresses which were not contacted or which refused to give any information will also have contained individuals from the eligible minority ethnic groups. The number of non co-operating households estimated to contain an eligible minority ethnic adult or child is shown in the rows labelled 'Estimated eligible among households not screened'. The estimate is based on the proportion of the eligible households at the screened addresses, and the row showing the 'Total estimated eligible households' is the sum of the known plus the estimated eligible households. Based on the estimated number of eligible households, household response overall was 67%. Table 14.8 shows the household response among the Chinese sample, which was a follow-up to an earlier survey as described in Section 14.2.8. Based on known eligible households, the household response rate in the Chinese sample was 81%; based on the estimated number of eligible households, it was 76%. 14.6.7 Boost sample: individual response - adults Adult response by sample type Response figures for individuals are shown firstly by sample type and then for each minority ethnic group. As in the general population sample, the number of eligible adults in sampled households is not known and must be estimated. While the number of eligible adults in co-operating households is known, this figure is not known for non co-operating households. Furthermore, as described in the previous section, the number of eligible households is itself an estimate (which is not the case in the general population sample), so the estimated eligible number of adults for the boost sample is consequently less reliable than that for the general population sample. Estimating the 'set' sample for the minority ethnic boost sample involved a number of stages:
8% of those seeing a nurse did not give a blood sample either because it was not possible to obtain a sample from them, for example because of collapsed veins (3%), or because they were ineligible to give blood (5%). People were ineligible if they had a specified health condition, were taking certain drugs, or were pregnant. Response to the interview stage was higher among women (61%) than among men (58%). This difference between the sexes persisted throughout the different survey stages. Adult response by minority ethnic group Table 14.11 shows response rates for each of the minority ethnic groups which were included in the boost sample, together with the Chinese sample. As informants from these minority ethnic groups (except Chinese) who were in the general population sample were given the same interview as minority ethnic informants from the boost sample and the two samples were combined for analysis, every response table by minority ethnic group includes all informants belonging to each group, whether they were sampled as part of the general population sample or the boost sample. Because of 'mixed' households - that is, households which contain individuals from more than one minority ethnic group - response rates are only shown at the individual level in these tables. Table 14.11 shows response rates based on the estimated 'set sample' for each minority ethnic group (with the 'set sample' being calculated in the manner described earlier in this section). Response to the interview stage was highest for Bangladeshis (66%), Irish (65%) and Chinese (62%), was similar for Pakistanis (60%) and Indians (59%), and was lowest for Black Caribbeans (55%). Response rates were higher for women than men in all minority ethnic groups: the largest difference was found among Black Caribbeans (59% women and 51% men). Although Bangladeshis had the highest interview response rate, they were the least likely to see a nurse, and thus had the lowest response rates at the second stage, including providing blood and saliva samples. Irish informants had the highest response rates to the nurse visit and for all later stages of the survey. Adult response in co-operating households by minority ethnic group Tables 14.13 and 14.14 show the proportion of men and women in co-operating households who responded to the key survey stages. These are shown below for the full sample of minority ethnic informants:
At the first stage interview, response within co-operating households was highest for Irish and Bangladeshis and lowest for Chinese. Response at all later stages was highest for the Irish and lowest for Bangladeshis. 14.6.8 Boost sample: individual response - children Overall response Interviews were carried out with 3,415 children from minority ethnic groups, including those identified in the boost, Chinese and general population samples (with information obtained from a parent for those aged 2-12). 2,387 children were seen by a nurse and 437 children aged 11 to 15 gave a blood sample. Table 14.10 shows the individual response rate for children in the minority ethnic boost sample. To compute the response rate, the number of eligible children in estimated eligible households (the 'set' sample) is needed as the denominator. Estimating the 'set' sample for the minority ethnic boost sample was described in Section 14.6.7. This was applied to children in the same way as for the the general population (Section 14.6.4). The estimated 'set' sample for children was 4,406 in the minority ethnic boost sample, which is the base found in Table 14.10. The estimated total number of children in the separate Chinese sample was 378. In the minority ethnic boost sample, response rates for children were:
The response rates within the boost sample were 64% for boys and 66% for girls at the interview stage. Table 14.12 shows response rates for children by minority ethnic group, including Chinese. As children from these minority ethnic groups (except Chinese) who were in the general population sample were given the same interview as minority ethnic informants from the boost sample and the two samples were combined for analysis, the response tables by minority ethnic group include all children belonging to each group, whether they were sampled as part of the general population sample or the boost sample. Response rates were highest for Bangladeshi, Chinese and Irish children and lowest for Black Caribbean children. Child response in co-operating households Response rates for minority ethnic children, calculated on a co-operating household base, are shown in Tables 14.15 for boys and 14.16 for girls. They are shown below for all children by minority ethnic group. Response to the interview was high among children from all minority ethnic groups, and a majority co-operated with the measurements and provided a saliva sample. Irish children had the highest levels of response at all stages. Bangladeshi children had a high level of response to the interview, but were the least likely to be seen by a nurse, so had the lowest levels of response for the measurements and samples taken at the second stage. The proportion of children aged 11 to 15 providing a blood sample varied between minority ethnic groups, with Pakistani and Bangladeshi children the most likely to refuse to give blood (25% and 29% respectively refused). While the proportion of Indian and Irish children giving blood samples was similar to that for the children from the general population in 1998, this, in turn, was much lower than in earlier survey years. The increasing reluctance of children to give blood samples appears to be a consequence of the change in protocol for obtaining blood from minors that was introduced in the 1998 survey (see Section 14.3.4).
14.7 Sample profile of those interviewed 14.7.1 Age profile of the general population sample This section compares the age and sex profiles of the general population sample with the 1999 mid-year population estimates (it should be noted that these population estimates cover both institutional and private residential populations, whereas the Health Survey only covers the private residential population). According to the mid-year 1999 population estimates men form 48.8% of all adults, while in the 1999 Health Survey general population sample they form 45.6% of all interviewed informants. Men aged under 35 are under-represented in the general population sample, while men aged 65 and over are slightly over-represented. Women aged under 35 and those aged 75 and over are both slightly under-represented in the sample. 14.7.2 Comparison of the minority ethnic group and general population samples Tables 14.18 to 14.28 compare the minority ethnic groups and the general population on a number of socio-demographic characteristics. (The results in these tables are not age-standardised.) Age The age distribution among the Irish was the most similar to that of the general population. Except for the Irish, all the minority ethnic groups had a considerably younger age profile than the general population. Whereas only 29% of men and women in general were aged under 35, the proportion of Pakistanis (53% men, 60% women) and Bangladeshis (51% men, 65% women) under 35 was much higher. The latter two groups were also much less likely to be aged 65 or over than men and women in the general population. Marital status Compared with the general population, South Asian and Chinese informants were more likely to be married and less likely to be divorced or widowed. Black Caribbean informants were considerably less likely than the general population to be married, and twice as likely to be single. The distribution of marital status among the Irish was similar to that for the population as a whole. Economic activity, social class and income Two in three men in the general population were in paid work (61%), while another 4% were unemployed or temporarily sick. The proportions in paid work were similar for the minority ethnic groups, except for Black Caribbean and Bangladeshi men with fewer than half being in paid work (48% and 42% respectively). Both had much higher rates of unemployment (two to three times as high as the general population), as did Pakistani men. A high proportion of Bangladeshi men said they were not working because they were looking after the family or home (12% compared with 1% of men in general). Men in all minority ethnic groups, except for the Irish, were more likely than men in general to be in full-time education, which is a reflection of the much younger age profile of these groups. By contrast, men in the general population were much more likely than men from the South Asian and Chinese groups to be retired, but rates of retirement were similar to those of Black Caribbean and Irish men. Half of women were in paid work (48%), a proportion which was similar across all minority ethnic groups except for Pakistani and Bangladeshi women, with fewer than one in five in work (18% and 15% respectively). At least three in five women in these two groups were looking after the family or home, compared with only one in five women in general. As was found among men, women from the minority ethnic groups were more likely than women in general to be in full-time education and were less likely to be retired; the exception was Irish women, who were very similar to women in general. Looking at the social class of the head of household, the distributions for Chinese, Indian and Irish men and women were similar to that for the general population, although the Indian and Irish groups were slightly less likely to be living in non-manual households than the population in general. For the Black Caribbean, Pakistani and Bangladeshi groups, the distributions were skewed towards the head of household being classified in a manual social class. This was particularly marked for the Bangladeshi group. The differences between these groups and the general population were mainly to be found in Social Classes IIIM and IV, as only a small proportion of informants lived in households headed by a person in Social Class V. Looking at equivalised household income tertiles (based on the income for the general population, and thus not the same variable used for analysis in the report), it can be seen that all minority ethnic groups except the Irish were more likely to be in the bott | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
indicate that it was asked of all informants, while those with a