The critical appraisal of focus group research articles

Objectives: To determine whether the three mailings routinely used by researchers for epidemiological surveys are useful and appropriate, by comparing social characteristics and selected disease histories to find out if there are differences between individuals responding at different times.

Methods: Social characteristics and selected disease histories of 11,797 British women still under general practitioner observation in the Royal College of General Practitioners' Oral Contraception Study were compared. The women aged 40-78 at December 1992 were sent health survey questionnaires via their general practitioners between November 1994 and July 1995.

Results: Significant differences in the characteristics of first, second and third mailing respondents and non-respondents were found for smoking habits, social class, parity, area of residence, further contact, bronchitis, hysterectomy and mental illness. First mailing respondents were more likely to be from a non-manual social class, have a parity of less than three, live in England, and be happy to be contacted again, but were less likely to have had bronchitis or mental illness and were less likely to have been smokers at the time of recruitment than second mailing respondents. A comparison of second and third mailing respondents on the above factors showed no significant differences between the two groups.

Conclusions: The inclusion of third mailing respondents did not significantly change the social or health characteristic profile of the cohort and suggests that the effort and resources expended in carrying out a third mailing may not be justified.     

Response patterns to a postal survey using a cervical screening register as the sampling frame

This study compared different types of respondent to a postal survey. A random sample of women aged 20-64 years (n = 4057) was selected from a population-based cervical screening register to examine their information experience during the screening programme. The initial response rate was 57%, and this increased to 81% after one reminder. Respondents were older (P < 0.0001) than non-respondents, but both groups were comparable with regard to attendance history for cervical screening (respondents 89.3%; non-respondents 89.1%) and normal smear test results (respondents 84.0%; non-respondents 81.4%). Early and late respondents were similar in age. Compared with late respondents, early respondents were more likely to live in highly affluent (P < 0.0001) and rural areas (P = 0.026). They were also more likely to be non-attenders (P < 0.0001), but they were less likely to have had inadequate smear results (P = 0.030) than late respondents. These results suggest that consideration should be given to factors other than sociodemographic differences when examining response patterns to postal surveys.     

Postal survey on airborne occupational exposure and respiratory disorders in Norway: causes and consequences of non-response.

STUDY OBJECTIVE--The aim was to examine causes for non-response in a community survey, and how non-response influences prevalence estimates of some exposure and disease variables, and associations between the variables. DESIGN--This was a cross sectional questionnaire study with two reminder letters. The questionnaire asked for information on smoking habits, occupational airborne exposure and respiratory disorders. SETTING--A random sample of 4992 subjects from the general population aged 15-70 years of Hordaland County, Norway. MAIN RESULTS--The overall response rate was 90%, with a 63% response to the initial letter. The response rates to the first and second reminder letters were 56% and 36% respectively. In 20% of the non-respondents an uncompleted questionnaire was returned with cause for non-response; in two thirds of these the cause for non-response was that the subject was not resident at the mailing address. A home visit to a random sample of 50 urban non-respondents provided further information on 29 subjects. A wrong address at the Central Population Registry and the subject's feeling of lack of personal benefit from a postal survey were the major reasons for non-response. Smokers were late respondents and subjects with respiratory disorders tended to be early respondents. CONCLUSION--The main reasons for non-response were a wrong mailing address and a feeling of lack of personal benefit from responding. Using only the initial letter would have changed the estimated prevalence of smokers from 39% to 35%. Otherwise, the estimated prevalence of the exposure and disease variables as well as the associations between them were only slightly changed after including the respondents to the first and second reminder letters.     

Characteristics of respondents and non-respondents from a case-control study of breast cancer in younger women

BACKGROUND: This study assessed the nature of potential biases by comparing respondents with non-respondents from a case-control study of breast cancer in younger women. METHODS: The case-control study was conducted in three regions in the US: Atlanta GA, Seattle/Puget Sound WA, and central New Jersey. An abbreviated interview or mailed questionnaire was completed by willing non-respondents, most of whom had refused participation in the main study. RESULTS: Respondents and non-respondents appeared similar with respect to age, race, relative weight, smoking, family history of breast cancer, number of births, age at first birth, and several dietary items. Compared to non-respondents, case and control respondents were of shorter stature, and reported less frequent consumption of doughnuts/pastries. Respondent cases, compared with non-respondent cases, were more highly educated and more likely to have consumed alcohol regularly; similar but not statistically significant tendencies were observed for controls. Respondent cases experienced menarche earlier than non-respondents. Respondent controls were more likely to have used oral contraceptives than non-respondents; a similar but not statistically significant tendency was observed in cases. Comparisons of crude and simulated relative risks using available non-respondents' data generally showed a low impact of non-response on relative risks in this study. CONCLUSIONS: Our results suggest that non-response would not greatly affect relative risk estimates in this study, except possibly regarding height. However, we were limited by the numbers of informative non-respondents and the amount of data collected. Collecting similar information in future studies would be useful, especially since varying methods used to encourage participation may lead to differences in respondents' characteristics.     

Estimating non-response bias in a survey on alcohol consumption: comparison of response waves

AIMS: According to 'the continuum of resistance model' late respondents can be used as a proxy for non-respondents in estimating non-response bias. In the present study, the validity of this model was explored and tested in three surveys on alcohol consumption. METHODS: The three studies collected their data by means of mailed questionnaires on alcohol consumption whereby two studies also performed a non-response follow-up. RESULTS: Comparisons of early respondents, late respondents and non-respondents in one study showed some support for 'the continuum of resistance model', although another study could not confirm this result. Comparison of alcohol consumption between three time response groups showed no significant linear pattern of differences between response waves. CONCLUSIONS: The hypothesis that late respondents are more similar to non-respondents than early respondents, could not be confirmed or rejected. Repeated mailings are effective in obtaining a greater sample size, but seem ineffective in improving the representativeness of alcohol consumption surveys.     

Effect on Trend Estimates of the Difference between Survey Respondents and Non-respondents: Results from 27 Populations in the WHO MONICA Project

Introduction: In the World Health Organization (WHO) MONICA (multinational MONItoring of trends and determinants in CArdiovascular disease) Project considerable effort was made to obtain basic data on non-respondents to community based surveys of cardiovascular risk factors. The first purpose of this paper is to examine differences in socio-economic and health profiles among respondents and non-respondents. The second purpose is to investigate the effect of non-response on estimates of trends. Methods:Socio-economic and health profile between respondents and non-respondents in the WHO MONICA Project final survey were compared. The potential effect of non-response on the trend estimates between the initial survey and final survey approximately ten years later was investigated using both MONICA data and hypothetical data. Results: In most of the populations, non-respondents were more likely to be single, less well educated, and had poorer lifestyles and health profiles than respondents. As an example of the consequences, temporal trends in prevalence of daily smokers are shown to be overestimated in most populations if they were based only on data from respondents. Conclusions: The socio-economic and health profiles of respondents and non-respondents differed fairly consistently across 27 populations. Hence, the estimators of population trends based on respondent data are likely to be biased. Declining response rates therefore pose a threat to the accuracy of estimates of risk factor trends in many countries.     

Marital status,educational level and household income explain part of the excess mortality of survey non-respondents

Survey respondents and non-respondents differ in their demographic and socio-economic position. Many of the health behaviours are also known to be associated with socio-economic differences. We aimed to investigate how much of the excess mortality of survey non-respondents can be explained by the socio-economic differences between respondents and non-respondents. Questionnaire-based adult health behaviour surveys have been conducted in Finland annually since 1978. Data from the 1978 to 2002 surveys, including non-respondents, were linked with mortality data from the Finnish National Cause of Death statistics and with demographic and socio-economic register data (marital status, education and household income) obtained from Statistics Finland. The mortality follow-up lasted until 2006, in which period there were 12,762 deaths (7,994 in men and 4,768 in women) during the follow-up. Total and cause-specific mortality were higher among non-respondents in both men and women. Adjusting results for marital status, educational level and average household income decreased the excess total and cause-specific mortality of non-respondents in both men and women. Of the total excess mortality of non-respondents, 41% in men and 20% in women can be accounted for demographic and socio-economic factors. A part of the excess mortality among non-respondents can be accounted for their demographic and socio-economic characteristics. Based on these results we can assume that non-respondents tend to have more severe health problems, acute illnesses and unhealthy behaviours, such as smoking and excess alcohol use. These can be reasons for persons not taking part in population surveys.     

Increasing response rates to a smoking survey for U.S. Navy enlisted women

This study examined the effectiveness of several persistent strategies to increase the response to a smoking survey among newly enlisted U.S. Navy women. The stepped approach, which included the use of incentives, repeated mailings, alternative survey administration modes, and reminders, was evaluated in terms of effects on response rates and response bias. Demographic and baseline smoking-related characteristics were compared for those responding on time to the initial mailed follow-up survey, reluctant respondents who did not respond initially but eventually completed a survey after further prompting, and non-respondents. Results showed that incentives and persistent efforts were effective in substantially increasing the response among 2,231 eligible participants, more than doubling the response rate (from 24.9% to 52.7%). The characteristics of on-time, reluctant, and non-respondents did not differ significantly in terms of sociodemographic characteristics. On the other hand, on-time respondents were different from both reluctant respondents and non-respondents in terms of smoking-related behaviors.     

Non-participation and mortality in different socioeconomic groups: the FINRISK population surveys in 1972-92

BACKGROUND: Declining response rates pose a serious threat to the validity of estimates derived from epidemiological studies. If respondents and non-respondents differ systematically from each other, there can be a bias in the results of the study. A population-based cohort study was conducted to investigate disparities in socioeconomic structure between respondents and non-respondents and the contribution of these disparities to socioeconomic differences in total and cardiovascular mortality. DESIGN: Data comprised 32,354 male and female participants and 4890 non-participants aged 35-74 years who belonged to the sample in one of the five FINRISK surveys in 1972, 1977, 1982, 1987 or 1992 in Finland. They were followed up for 9 years and 6 months. RESULTS: It was found that the lower socioeconomic groups were over-represented among non-respondents both in men and women. When comparing the relative risk of death using the highest socioeconomic group of the participants as the reference group, it was found that although the socioeconomic gradient was similar for participants and non-participants-that is, lower groups had a higher risk of death-the risk was at a higher level among non-respondents. CONCLUSIONS: Basing analysis on participants does not distort the relative risk of death associated with socioeconomic position. However, it does underestimate the absolute risk.     

Patterns of Survey Attrition and Reluctant Response in the 1996 Medical Expenditure Panel Survey

In panel designs with multiple waves of data collection, the overall survey response rate is a multiplicative function of the wave specific response rates. The 1996 Medical Expenditure Panel Survey (MEPS) follows this model, requiring five rounds of data collection with the same panel of sampled households, to acquire data on health care use, expenditures, insurance coverage and sources of payment that cover two consecutive calendar years. Gaining an understanding of the factors that distinguish the cooperative respondents, the survey participants that require use of nonresponse conversion techniques to maintain their cooperation (reluctant respondents), and the initial participants that eventually drop out of the survey (part-year respondents) is essential from both an estimation and data collection perspective. To inform the specification of nonresponse adjustment strategies in MEPS to correct for survey attrition, this study attempts to identify the characteristics that distinguish survey participants across rounds from the part-year respondents. In addition, the study identifies factors that distinguish the cooperative respondents, the reluctant respondents and the part-year respondents, to better inform the MEPS data collection effort. The investigation also examines the implications of a data collection strategy that would not convert initial survey refusals by studying the effect, on survey estimates and their precision, of excluding reluctant survey respondents.Our findings revealed that reluctant respondents in the first round of the survey were significantly more likely to become non-respondents in the second round. In addition, the round two non-respondents were also more likely to be located in large metropolitan areas, to reside in the larger households with 5 or more members, to be elderly, and more likely to be either married or separated. Many of these characteristics were similar to those found to be at higher risk for nonresponse to the round one interview. Reluctant respondents as a whole appear to be a distinctly separate group, sharing one set of characteristics with the cooperative respondent group, another set with those who refused during the second round of the survey, and yet a third set of characteristics that are uniquely their own. If no effort had been made to convert reluctant participants, the precision of our survey estimates would have declined, but not substantially.