Scientific Institute of Public Health (IPH) Health Interview Survey 2001 Protocol for the Sampling Design Version July 20, 2001 Wetenschappelijk Instituut voor Limburgs Universitair Centrum Volksgezondheid Center for Statistics Dienst Epidemiologie Bruckers Liesbeth Demarest Stefaan Molenberghs Geert Tafforeau Jean Tibaldi Fabián Van Oyen Herman Van Steen Kristel 1. INTRODUCING THE HEALTH INTERVIEW SURVEY 4 1.1 Objectives of the survey 4 1.2 Target population, study population and the sampling frame 5 2. SAMPLING DESIGN 7 2.1 Introduction 7 2.2 Sample Size 7 2.3 Stratified Clustered Multi-stage design 8 2.3.1 Motivation 8 2.3.2 Overview of the design 9 3. NON RESPONSE 13 3.1 Non-response at household level 13 3.2 Non-response at Individual Level 15 4. PROCEDURE IMPLEMENTATION 16 4.1 Stratification 16 4.2 Multi stage sampling 17 4.3 Systematic sampling 18 4.4 Clustering: Selection of a sets of households within each municipality 22 4.5 Advantages of the design 26 4.6 Activation of the households 26 4.6.1 Replacement of the households 28 4.6.2 Quarters 2-4 30 4.7 Selection of the household members 31 5. CONTACTING THE RESPONDENTS 32 5.1 The announcement of the survey 33 5.2 Procedure for contacting a household 33 5.3 Selection of the respondents 36 5.3.1 Note on non-coverage 38 6. INTERVIEWERS AND FIELDWORK 40 6.1 Training 40 6.2 Guidelines 41 6.2.1 Use of proxies 41 6.2.2 Institutionalized Elderly People 42 6.2.3 Interpreter 43 7. QUALITY CONTROL BOARD 44 7.1 Indicators for the fieldwork 45 2 7.1.1 Management of the interviewers 46 7.1.2 Performance of the interviewers 46 7.1.3 Quality of the fieldwork 48 7.1.4 Progress of the fieldwork 48 8. APPENDICES 51 8.1 Selected Sample 51 8.1.1 Introduction 51 8.1.2 The distribution over the regions 52 8.1.3 The distribution over the provinces 53 8.1.4 The systematic sampling of the municipalities 53 8.1.5 The selection 57 8.2 Graphs corresponding to the selection procedure 63 8.3 Indicators for the Fieldwork 69 9. LIST OF ABBREVIATIONS 71 10. REFERENCES 72 3 1. Introducing the Health Interview Survey 1.1 Objectives of the survey The main objective of the Health Interview Survey is to give a description of the health status of the population in Belgium in general and of the three regional subpopulations (Flemish, Walloon and Brussels region) in particular. The idea is to obtain information on how people experience their health, to what extent they make use of health care facilities, and how they look after their health by adopting a certain life style or relying on preventive and other health services. More specifically, the goals of the survey can be summarized as follows: · Identification of health problems · Description of the health status and health needs of the population · Estimation of prevalence and distribution of health indicators · Analysis of social (in)equality in health and access to the health services · Study of health consumption and its determinants · Study of possible trends in the health status of the population A health interview survey provides one possible channel through which such information can be obtained. On the basis of this survey, assessing a large variety of personal, social and material characteristics, life habits and conditions, determinants for public health can be traced and identified. The ultimate goal of the health interview survey is to be an integrated instrument in decision making, while mapping out an adequate health policy. The aim is stating priorities in policy development and to monitor the progress of populations’ health. 4 1.2 Target population, study population and the sampling frame The objective of the Health Interview survey – i.e. to give a description of the health status of the population in Belgium-, leads to the broad definition of the target population as all people residing in Belgium. Due to (1) the selection of a sample frame and (2) practical considerations and decisions, not all persons belonging to this target population will or can be considered for the survey. This means that the study population – the population that can be defined accurately and reached in the study – does not cover de target population completely: (1) As a consequence of using the National Register as the sample frame, people not listed in the Register (homeless) are excluded from the survey but also new created households are sometimes not registered. (2) Not individuals, but households will be invited to participate in the survey. A household is defined as all people living at the address of the reference person. The selection of households is consequently a selection of reference persons. This implies that people not living with a reference person listed in the National Register are excluded from the survey. Furthermore, it was decided not to include ‘specific’ households, that is, households with a reference person living in · an institution, with the exception of institutions for elderly · a religious community or cloister with more than 8 persons · a prison · a psychiatric institution · a health institution Excluding these households from the survey generates specific problems for the fieldwork, since only the ‘specificity’ of the household can be known. The National Register does no contain information whether the address is an institution, prison,…. These problems will be discussed in depth in Section 5.2. Although the most actual version of the National Register is used, the situation of households can be different than the one used in the Register; one of the most important advantages is that the NIS has a direct access of the NR and this is a kind of constantly updated information. Even though when a change occurs in within the household it may take up to 1 month before the information in the Register is updated (these changes have to reported to the local authorities and 5 transmitted to the Register). Given the use of a progressively deteriorating National Register copy, a verification process is necessary. This verification process will identify households that are no longer eligible or households, which need an update of the reference person or the address. This is done as late as possible, approximately one month before each quarter. Two criteria are checked (1) the vital status of the reference person and (2) the current address of the main residence of the reference person. This control is conducted in an automated fashion. Only in the case the reference person died in a household with two or more members and there is no partner (less than 1 percent of the selected households), a manual on-line search is necessary. The time needed for the control process is approximately 1 week. Even when using the most actual version of the National Register, the real composition of a household can be different compared to the administrative composition. Next to the fact that it takes some time before the Register is adapted, remains the fact that households neglect, find it unnecessary or do not want to report changes. General guideline for the interviewers is that the real situation ALWAYS overrules the administrative situation. This means e.g. that · when an ‘administrative’ member left the household for a period of at least one-year, he/she will be considered as not being a member of the household. This rule is not applicable for elderly people, who have their official address in the household while remaining in an institution for the elderly. · compared to the administrative data, new members can have joined the household. As far as these are not considered as guests, they should be treated as being a member of the households. 6 2. Sampling Design 2.1 Introduction Sample surveys can be distinguished from other statistical collections by their particular approach to two questions. The first concerns the units from which the population data are to be collected (the sample selection). The second relates to how to infer relevant conclusions, including estimates, concerning the population surveyed is from the data collected. Sampling theory is concerned with the answers to these two questions (Ref 10). In this chapter we will introduce and motivate the procedure used to select units from the target population which has been delineated in Section 4. The results of sample surveys are always subject to some uncertainty because only part of the population has been included and because of errors of measurement. Simply increasing the sample size costs both in terms of time and money. Hence, the specification of the degree of precision wanted in the results is an important consideration. 2.2 Sample Size The total number of successful interviews for the sample of 2001 is set to 10,000. This sample size is based on sample size calculations performed during pre-analyses for the health interview survey 1997 (Ref 16), taking into account specific budget constraints and the available logistic means. On the basis of the preliminary reports and the analysis of the HIS 1997 (Ref 16), the efficiency obtained in estimation at the national and regional level appeared to be sufficient. It was however too small for estimation purposes at the provincial level. In order to answer specific requirements of the provinces in the HIS2001, provinces were encouraged to make extra funds available, enabling a province-specific analysis. To keep the fieldwork within limits, it was decided not to exceed 13,000 as a total number of interviews. Four provinces agreed to pay for the oversampling and to increase the number of interviews within their province.