Scottish Survey
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the Scottish survey1998 VOLUME 2 A SURVEY CARRIED OUT ON BEHALF OF THE SCOTTISH EXECUTIVE HEALTH DEPARTMENT EDITED BY ANDREW SHAW, ANNE MCMUNN AND JULIA FIELD JOINT HEALTH SURVEYS UNIT, AT THE NATIONAL CENTRE FOR SOCIAL RESEARCH AND DEPARTMENT OF EPIDEMIOLOGY & PUBLIC HEALTH, UCL NOVEMBER 2000 © Crown copyright 2000 First published 2000 Not to be sold separately ISBN 1 84268 085 4 ii CONTENTS VOLUME 2: TECHNICAL REPORT 15 METHODOLOGY AND RESPONSE........................................................................1 Kavita Deepchand, Johanna Laiho 15.1 Introduction.................................................................................................................2 15.2 Survey design and fieldwork procedures....................................................................2 15.3 Interviewing and measuring children .........................................................................3 15.4 Survey coverage..........................................................................................................4 15.5 Ethical clearance.........................................................................................................5 15.6 Sample selection .........................................................................................................6 15.7 Survey response ..........................................................................................................9 15.8 Weighting..................................................................................................................10 15.9 Comparison of the responding sample with the general population........................14 15.10 The accuracy of the survey results ...........................................................................14 15.11 Social class variables ................................................................................................15 Tables ..................................................................................................................................17 16 QUALITY CONTROL OF BLOOD AND SALIVA ANALYTES .........................35 Marion Brookes and Anne McMunn with John Sprunt, Paul Finglas and Ian Gibb 16.1 Introduction and key conclusions .............................................................................35 16.2 Samples collected .....................................................................................................35 16.3 Change of analysing laboratories .............................................................................36 16.4 Methodology.............................................................................................................36 16.5 Quality control ..........................................................................................................39 Tables ..................................................................................................................................45 APPENDICES A Fieldwork documents................................................................................................77 B Measurement protocols...........................................................................................183 C Health Board areas..................................................................................................217 D Glossary ..................................................................................................................219 iii iv 15 METHODOLOGY AND RESPONSE 15 Kavita Deepchand, Johanna Laiho SUMMARY I 77% (9093) of the eligible sample of households (people in private households aged 2 – 74) completed at least one individual interview. 76% (9047) of eligible adults and 75% (3892) of eligible children completed an individual interview. I 82% (7455) of interviewed adults (3287 men and 4168 women) and 83% (3211) of children (1625 boys and 1586 girls) were visited by a nurse. I 68% (6178) of the eligible sample of adults gave a blood sample (with a further 3% who agreed to give a blood sample but from whom one could not be obtained). 46% (466) of the eligible sample of children (aged 11 – 15) gave a blood sample. I Blood samples were more likely to be obtained from men than women (of those visited by a nurse, blood samples were obtained from 85% of men and 81% of women). I For adults, response rates at most stages were lowest amongst the youngest age group (16 – 24). 1 15.1 INTRODUCTION The objective of the Scottish Health Survey was to provide data about the health of the population aged 2 to 74 living in private households in Scotland. This volume of the report describes the technical aspects of the survey. Chapter 15 deals with the methodological issues including sampling, weighting and standard error estimations. It also describes the survey’s coverage, fieldwork procedures and response rates. Chapter 16 deals with the blood analytes: laboratories used, procedures and quality. 15.2 SURVEY DESIGN AND FIELDWORK PROCEDURES This section outlines the timing of the survey, the fieldwork procedures and the coverage of the survey. Interviewing began in April 1998, and was carried out over a 13 month period. The random sample of addresses was selected from 312 postcode sectors, and in each month of the first twelve months, addresses in 26 sectors were issued to interviewers. Further details of the sample design are given in Section 15.6. An advance letter was posted to each sampled address at the beginning of the relevant fieldwork month. This informed residents that their household had been selected for inclusion in the survey. Every address was then visited by an interviewer. One adult from each household provided basic information about the members of the household. The interviewer then randomly selected, for the main interview, one resident adult aged between 16 and 74 years old and a maximum of two resident children aged between 2 and 15. If there were no residents within the relevant age range at the address, no interview was attempted. The sample was designed to ensure that every household within a region was given an equal chance of selection. This was done by taking into account the Multiple Occupancy Indicator (MOI) at the sample selection stage. However, we still needed to implement a strategy for dealing with addresses where the MOI equals 1, but which actually contain more than one household. Where the actual number of households was three or less, all household units were included in the sample. Where the number of households was greater than three, three household units were randomly selected by the interviewer using specially- designed random number tables attached to each Address Record Form and a corrective weight applied at the analysis stage. The Address Record Form is a document which provides interviewers with the sample addresses and selection instructions, onto which they write details of calls to the address and record their selection procedures. Unlike the 1995 survey where nurses used a paper questionnaire, both interviewers and nurses for the 1998 Survey used Computer-Assisted Personal Interviewing (CAPI). This entails informants’ responses being entered directly into a laptop computer. A description of the content of the individual and nurse interviews is given in Section 15.4. Interviewers also took height and weight measurements of all those interviewed. At the end of the interviewer-administered interview, informants were asked if they would be willing to take part in the next stage of the survey - the nurse visit. For those who agreed, an appointment was made for the nurse to visit within a few days of the interview. The nurse interview entailed collecting the names of any prescribed medicines and taking further anthropometric measurements (waist, hip, mid-upper arm circumference and demi-span) and small saliva and blood samples. Nurses also took blood pressure measurements and administered a lung function test. Each test tube (containing either blood or saliva) was clearly labelled with the informant’s serial number and date of birth. Tubes for each informant were packed separately from 2 those of other members of the household. The tubes were put in a larger plastic container and placed inside a pre-paid box and sent to the Royal Victoria Infirmary in Newcastle. A small sub-sample of blood samples was sent to the Institute of Food Research in Norwich. Further details of the blood analysis may be found in Chapter 16. In addition to the advance letter, informants were given two further leaflets: one by the interviewer that described the purpose of the survey and one by the nurse that explained the measurements taken during the nurse visit. Copies of these are contained in Appendix A. Every informant was given a Measurement Record Card in which interviewers and nurses entered the informant’s height and weight; waist and hip or arm circumference, or demi-span (as appropriate); blood pressure and lung function values. With their agreement, informants were also later sent the results of their blood sample analyses and, with their written consent, informants’ blood pressure, lung function and blood sample analyses were also sent to their GP. Nurses were issued with a set of guidelines to follow when commenting on informants’ blood pressure readings (see Appendix B for details). The nurse was instructed to contact the Survey Doctor as soon as feasible whenever an adult informant had severely raised blood pressure. They were instructed not to comment on a child’s reading. Where permission had been given for results to be sent to an