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.     

Comparison of telephone and postal survey modes on respiratory symptoms and risk factors

Little is known about the comparability of postal and telephone survey modes in epidemiology. A cross-sectional, population-based study (n = 25,000) of lung disease was performed in 1998-1999 in two regions of Norway. Initial surveying was done by postal questionnaire. A 1% random sample (n = 171) of previous postal responders were resurveyed by telephone or cellular contact. The response rate was 67% on the telephone/cellular interview. Fewer incomplete answers were given by telephone than by mail. A lower prevalence was found by telephone for morning cough and exposure to passive smoking at work or home. Reproducibility was high for asthma, hay fever, wheezing, and attacks of breathlessness. Moderate reproducibility was seen for symptoms of chronic bronchitis. Reproducibility was low for indoor and work environment, although it was high for early life factors. Concordance coefficients were high for all continuous measures such as height, body weight, and pack-years. The authors conclude that the comparability between the postal and the telephone survey modes was good. The telephone survey mode gave more complete information. Survey mode may have a moderate effect on study results, depending on the specific questions asked.     

Assessing research outcomes by postal questionnaire with telephone follow-up. TOTAL Study Group. Trial of Occupational Therapy and Leisure

BACKGROUND: Face-to-face assessment of research outcomes is expensive and may introduce bias. Postal questionnaires offer a cheaper alternative which avoids observer bias, but non-response and incomplete response reduce the effective sample size and may be equally serious sources of bias. This study examines the extent and potential effects of missing data in the postal collection of outcomes for a large rehabilitation trial. METHODS: Questionnaires containing a number of established scales were posted to participants in a trial of occupational therapy after stroke. Response was maximized by telephone and postal reminders, and incomplete questionnaires were followed up by telephone. Scale scores obtained by imputing values to questionnaire items missing on return were compared with those achieved by telephone follow-up. FINDINGS: Response to the initial posting was 60%, rising to 85% after reminders. Participants receiving the experimental treatment were more likely to respond without a reminder. There were no significant differences on any known factors between eventual responders and non-responders. Of the questionnaires, 43% were incomplete on return: partial responders were significantly different to complete responders on baseline disability and home circumstances. Of the incomplete questionnaires, 71% were resolved by telephone follow-up. In these, the scale scores achieved by telephone were generally higher than those derived by conventional imputation. CONCLUSION: Postal outcome assessment achieved a good response rate, but considerable effort was needed to minimize non-response and incomplete response, both of which could have been serious sources of bias.     

Nine-year follow-up of a survey on smoking habits in Florence (Italy): higher mortality among non-responders

BACKGROUND: Smoking prevalence is often assessed in random samples of a population. Non-response bias has been rarely investigated. METHODS: In 1989 a survey on smoking habits in Florence, Italy, was carried out (response rate: 85%). For responders and non-responders (3,621 subjects) the life status as of 1998 was assessed. Poisson regression models were fitted to estimate age-adjusted risks of death (RR) of non-responders for overall mortality and for the most important causes of death, taking the whole series of responders, postal responders and telephone responders as the reference in different analyses. This analysis included 2,071 subjects aged >/=45 years. RESULTS: Compared to the whole series of responders, mortality from all causes was significantly higher among non-responders in males (RR = 1.74; 95% CI: 1.23-2.44) and females (RR = 2.45; 95% CI: 1.79-3.29). The higher risk was seen for smoking-related and 'other' causes of death. Among females the difference was more evident for smoking-related causes (RR = 3.14; 95% CI: 1.66-5.93), among males the higher risk was similar for both groups of causes. The excess of mortality was less evident when telephone responders alone were taken as reference. CONCLUSIONS: The follow-up of subjects enrolled in a survey on smoking habits shows high mortality risks among non-responders. The data indirectly suggest that smoking was (or had been) more widespread among non-responders, in particular among females. Therefore, the prevalence of smokers assessed through this survey, focussed on smoking habit, may be underestimated. Telephone contact with non-responders to the postal questionnaire attenuated the selection bias of responders, but even with telephone back-up the response bias persisted.     

Nonresponse bias and cost-effectiveness in a Norwegian survey of family physicians

Low response rates are a common problem in surveys of family physicians leading to uncertainty about the validity of results. In this study, the authors examined the association between multiple reminders and nonresponse bias, survey estimates and costs in a survey of family physicians in Norway (N = 3,463). After three postal reminders and one telephone follow-up, the response rate was 65.9%. They analyzed differences in nine demographic and practice variables between respondents and nonrespondents, the effect of nonresponse bias on survey estimates, and the cost-effectiveness of each reminder. Statistically significant differences between respondents and nonrespondents were found for six variables. However, demographic and practice variables had little association with the main outcome variables, and the overall survey estimates changed little with additional reminders. In addition, the cost-effectiveness of the final reminders was poor.     

Investigating non-response bias in a survey of disablement in the community: implications for survey methodology.

STUDY OBJECTIVE--The aim was to investigate the pattern of age specific non-response bias in a two phase survey of disablement in the community. It seeks to examine patterns of response in different age groups to a household based postal questionnaire, and the implication of such trends for the estimation of prevalence of reported dependence. It also looks at the effect that the readiness to respond during the first phase postal questionnaire had on participation in the interview based second phase of the study. DESIGN AND SETTING--A two stage survey of disablement in the population was undertaken. A first phase postal questionnaire was sent to 25,168 households in Calderdale, West Yorkshire, England, to ascertain the prevalence of physical disability. The second phase comprised in depth interviews with a sample of individuals identified in the first phase as being disabled. RESPONDENTS--A total of 21,889 postal questionnaires were returned (87%) representing households containing 42,826 people aged 16 years and over. A disproportionately stratified random sample of 950 respondents reporting disability was taken for the second phase. Of these 891 were still available, and 838 (94%) were interviewed. MEASUREMENTS AND MAIN RESULTS--A study of the timing of response to a postal questionnaire showed that patterns differed for different age groups. The estimated prevalence of those aged 65 years and over who were dependent was steady over time whereas for those in the 16-64 age range the estimated prevalence fell as the survey progressed, indicating a tendency for those who were dependent to respond sooner. Examination of the relationship of responses at phase 1 and phase 2 showed that response to invitation to interview was much less in those who had responded later, and presumably more reluctantly, in the first phase. CONCLUSIONS--These findings raise questions about how different patterns of response might be indicative of bias which could differentially affect final age specific prevalence estimates. They also have methodological implications for the follow up of reluctant responders both to increase the response rate and to secure cooperation in the second phase of a two phase survey.     

Random digit dialling and Electronic White Pages samples compared: demographic profiles and health estimates

OBJECTIVE: To compare the methodologies of and health estimates derived from two telephone household survey methods. In particular, to establish if White Pages telephone listings provide a relatively unbiased sampling frame for population health surveys. METHOD: In South Australia in 1998, a health survey questionnaire was administered by telephone to two randomly selected population samples. The first method used EWP (Electronic White Pages, n = 6,012), which contains all listed residential telephone numbers as the sampling frame. The results were compared to a RDD (random digit dialling, n = 3,080) sample where all listed and unlisted telephone numbers were included in the sampling frame. Demographic variables and health estimates were compared between the surveys, and then compared to a 'gold standard' door-to-door household survey conducted concurrently. RESULTS: The response rate for EWP (83.8%) exceeded that of RDD (65.4%). More than four times as many calls were required per completed interview in RDD. Demographic profiles and health estimates were substantially similar. CONCLUSIONS: EWP requires fewer telephone calls and enables approach letters establishing the bona fides of the survey to be sent to each selected address before calling, increasing the response rate. RDD is a more inclusive sampling frame but also includes non-connected and business numbers, and offers no significant advantages in providing health estimates. IMPLICATIONS: There are substantial methodological and cost advantages in using EWP over RDD as the sampling, frame for population health surveys, without introducing significant bias into health estimates.     

Increasing response rates of gynaecologists to a survey: a randomised trial of telephone prompts

Abstract: This study used a randomised controlled trial to evaluate the effectiveness of telephone prompts to increase the response rate of gynaecologists to a survey. A nine-page questionnaire about management of women with abnormal Pap smears was mailed to Fellows of the Royal Australian College of Obstetricians and Gynaecologists. A random sample was contacted in advance by telephone, and nonrespondents received a telephone reminder 14 days after the initial mail-out. The control group was mailed questionnaires and a reminder letter conventionally. On Day 25, nonresponders in both groups were mailed a second questionnaire. Of the intervention group, 84 per cent responded to the survey compared to 69 per cent of the control group (P = 0.005). A telephone call in anticipation of a mailed questionnaire is highly recommended.     

Participation in breast cancer screening: randomised controlled trials of doctors' letters and of telephone reminders

Abstract: The study used a randomised controlled trial to find out whether supporting letters from general practitioners accompanying the invitations from a screening centre affected participation in a population-based breast cancer screening program for women aged 50 to 64. A further randomised controlled trial compared the effect of postal reminders with telephone reminders for women who did not respond to an initial invitation to participate in the program. There were 482 women in the first trial and 641 in the second. Excluding women who were ineligible or could not be contacted, participation in screening was 71 per cent in the group which received letters from their general practitioners compared with 62 per cent in the group which did not receive letters (P = 0.059). In the group that received letters, 56 per cent were screened without a reminder compared with 43 per cent of the group that did not receive letters (P = 0.01). Fewer women who received letters from their general practitioners declined the invitation to be screened (P = 0.048). In the second trial, there was no difference in participation between the group receiving telephone reminders and the group receiving postal reminders. As in breast cancer screening programs in other countries, general practitioner endorsement of invitations increased participation in breast cancer screening. Postal reminders were as effective as telephone reminders in encouraging women who did not respond to an initial invitation to participate in screening.     

Not another questionnaire! Maximizing the response rate, predicting non-response and assessing non-response bias in postal questionnaire studies of GPs

BACKGROUND: Non-response is an important potential source of bias in survey research. With evidence of falling response rates from GPs, it is of increasing importance when undertaking postal questionnaire surveys of GPs to seek to maximize response rates and evaluate the potential for non-response bias. OBJECTIVES: Our aim was to investigate the effectiveness of follow-up procedures when undertaking a postal questionnaire study of GPs, the use of publicly available data in assessing non-response bias and the development of regression models predicting responder behaviour. METHOD: A postal questionnaire study was carried out of a random sample of 600 GPs in Wales concerning their training and knowledge in palliative care. RESULTS: A cumulative response rate graph permitted optimal timing of follow-up mailings: a final response rate of 67.6% was achieved. Differences were found between responders and non-responders on several parameters and between sample and population on some parameters: some of these may bias the sample data. Logistic regression analysis indicated medical school of qualification and current membership of the Royal College of General Practitioners to be the only significant predictors of responders. Late responders were significantly more likely to have been qualified for longer. CONCLUSIONS: This study has several implications for future postal questionnaire studies of GPs. The optimal timing of reminders may be judged from plotting the cumulative response rate: it is worth sending at least three reminders. There are few parameters that significantly predict GPs who are unlikely to respond; more of these may be included in the sample, or they may be targeted for special attention. Publicly available data may be used readily in the analysis of non-response bias and generalizability.     

Impact of a postcard versus a questionnaire as a first reminder in a postal lifestyle survey.

STUDY OBJECTIVE--The study aimed to consider the impact of two different types of reminder on response rates and costs in a postal survey. DESIGN--The study was a cross sectional survey. A self-completion lifestyle questionnaire was used. Those who did not respond after the initial mailing were randomly allocated to receive either a postcard or questionnaire as a first reminder. All outstanding non-responders received a questionnaire as a second reminder. SUBJECTS--A representative sample of 698 adults aged 16-70 was used, drawn from a family health services authority register. MAIN RESULTS--Postcard reminders were as effective as questionnaire reminders in increasing response whether one or two reminders are sent. The costs per response were calculated. Two questionnaires as reminders were found to be 1.7 times more expensive than a postcard plus questionnaire. Including the initial mailing, the cost per response using all questionnaires was 1.3 times the cost when a postcard was used for the first reminder. CONCLUSIONS--To increase the response to a postal survey effectively and economically, two reminders should be sent--first a postcard and then a questionnaire.     

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.     

Sexual problems: a study of the prevalence and need for health care in the general population

BACKGROUND: There has been little research carried out on the prevalence and types of sexual dysfunction in the general population, although the indications are that such problems are relatively common. Most common sexual problems are potentially treatable. However GPs have estimated the prevalence of sexual problems to be far lower than survey estimates. OBJECTIVE: To provide an estimate of the prevalence of sexual problems in the general population, and assess the use of and need for professional help for such problems. METHODS: We used an anonymous postal questionnaire survey. The study was set in four general practices in England*, and the study population was a stratified random sample of the adult general population (n = 4000). The subjects were 789 men and 979 women who responded to the questionnaire. The main outcome measures were the presence and type of current sexual problems in men and women, and the provision and use of treatments for sexual problems. RESULTS: A response rate of 44% was obtained. The median age of the responders was 50 years. A third of men (34%) and two-fifths of women (41 %) reported having a current sexual problem. The most common problems were erectile dysfunction (n = 170) and premature ejaculation (n = 88) in men; in women the most widely reported problems were vaginal dryness (n = 186) and infrequent orgasm (n = 166). In men, the proportion of responders reporting sexual problems increased with age, but there was no similar trend in women. Of those responders who reported a sexual problem, 52% said that they would like to receive professional help for this problem, but only one in ten of these people (n = 50) had received such help. CONCLUSION: Among responders there was a high level of reported sexual problems. The most frequently reported problems (vaginal dryness, erectile problems) may be amenable to physical treatment in practice, and yet few had sought or received help. However, many said that they would like to receive help. These figures suggest that there may be an important burden of potentially reversible sexual problems in the general population.     

Patient views on reminder letters for influenza vaccinations in an older primary care patient population: a mixed methods study

OBJECTIVES: To explore the perspectives of older adults on the acceptability of reminder letters for influenza vaccinations. METHODS: We randomly selected 23 family physicians from each Family Health and Primary Care network participating in a demonstration project designed to increase the delivery of preventive services in Ontario. From the roster of each physician, we surveyed 35 randomly selected patients over 65 years of age who recently received a reminder letter regarding influenza vaccinations from their physician. The questionnaires sought patient perspectives on the acceptability and usefulness of the letter. We also conducted follow-up telephone interviews with a subgroup of respondents to explore some of the survey findings in greater depth. RESULTS: 85.3% (663/767) of patients completed the questionnaire. Sixty-five percent of respondents recalled receiving the reminder (n=431), and of those, 77.3% found it helpful. Of the respondents who recalled the letter and received a flu shot (n=348), 11.2% indicated they might not have done so without the letter. The majority of respondents reported that they would like to continue receiving reminder letters for influenza vaccinations (63.0%) and other preventive services (77.1%) from their family physician. The interview participants endorsed the use of reminder letters for improving vaccination coverage in older adults, but did not feel that the strategy was required for them personally. CONCLUSIONS: The general attitude of older adults towards reminder letters was favourable, and the reminders appear to have contributed to a modest increase in influenza vaccination rates.     

The effect of telephone reminders on attendance in respiratory outpatient clinics

INTRODUCTION: Patient non-attendance is an area of concern for all health care providers. A randomized controlled trial was undertaken to investigate whether reminder telephone calls improved attendance at respiratory outpatient clinics in the English National Health Service (NHS). METHODS: Patients were randomly allocated into one of two groups, either telephone reminder group or usual care. The telephone reminder group received a reminder telephone call between 9 am and 5 pm during the week prior to their appointment. Attendance and demographic information (age, sex, diagnosis and home postcode) were recorded. RESULTS: A total of 504 patients were recruited, 258 patients were allocated to the control group and 246 patients were allocated to the telephone reminder group. Fifty-eight percent of the patients allocated to the telephone reminder group were not contactable. Within the telephone reminder group, of the 104 patients who could be contacted, 86% attended. There was a significant 15% increase in attendance in the contacted group (n = 104) when compared both with the control group (71%, n = 258) and with the patients who could not be contacted (68%, n = 142) (P = 0.007; P = 0.004). It was estimated that the cost of telephoning 200 patients could be offset by preventing one non-attendance. CONCLUSION: Routine telephoning of outpatients should become standard practice if reducing non-attendance is thought to be desirable, but general practitioner (GP) referral letters and hospital records of current hospital outpatients need to include an up-to-date telephone number. Consideration should be given to 'out-of-hours' reminder calls to maximize the contact rate.     

Random digit dialing and directory-based samples in telephone surveys of HIV risk: a comparison from the Australian Study of Health and Relationships

PURPOSE: To compare the estimates of HIV-related risk derived from a sample drawn through random digit dialing and that component of the sample drawn from households listed in a telephone directory. METHODS: The prevalence of key outcomes, and their 95% confidence intervals, was estimated for the total sample and for that component of the sample drawn from households listed in a telephone directory. RESULTS: On all outcome measures the sample derived from listed households was more conservative. With few exceptions, the estimates derived from the overall sample and from listed households were not significantly different. CONCLUSION: A continued reliance on random digit dialing seems unwarranted.     

Determinants of non-response in an occupational exposure and health survey in New Zealand

Objective: Study the determinants of non‐response and the potential for non‐response bias in a New Zealand survey of occupational exposures and health. Methods: A random sample of 10,000 New Zealanders aged 20–64 years were invited by mail to take part in a telephone survey. Multiple logistic regression was used to study the determinants of non‐response. Whether occupational exposure, lifestyle and health indicators were associated with non‐response was studied by standardising their prevalence towards the demographic distribution of the source population, and comparing early with late responders. Results: The response rate was 37%. Younger age, Māori descent, highest and lowest deprivation groups and being a student, unemployed, or retired were determinants of non‐contact. Refusal was associated with older age and being a housewife. Prevalence of key survey variables were unchanged after standardising to the demographic distribution of the source population. Conclusions: Following up the non‐responders to the mailed invitations with telephone calls more than doubled the response rate and improved the representativeness of the sample. Although the response rate was low, we found no evidence of major non‐response bias. Implications: Judgement regarding the validity of a survey should not be based on its response rate.     

Use of patient reminder letters to promote cancer screening services in women: A population-based study in Wisconsin.

BACKGROUND: Patient reminder letters are an effective method of promoting cancer screening services in women; however, information on their actual use in a population setting is lacking. METHODS: Data were obtained from a population-based, random digit dial telephone survey of 896 adult women living in Wisconsin. Respondents were asked if they had received a reminder letter for Pap or mammography screening within the past year. RESULTS: Among women aged >/=18 years, 12.9% (95% confidence interval [95% CI] = 10.1-15. 6) received a Pap test reminder within the past year, while 13.0% (95% CI = 9.3-16.7) of women aged >/=40 years received a mammography reminder. Women without health care coverage were unlikely to receive either type of reminder. Current compliance with screening recommendations was greater among those women who received a reminder letter for Pap tests (94.3 versus 78.1%, P < 0.0001) and for mammography (81.7 versus 59.4%, P < 0.001). In contrast to the infrequent use of cancer screening reminders, 54.2% (95% CI = 50. 1-58.3) and 72.7% (95% CI = 67.6-77.8) of women reported receiving a reminder letter from their dentist or veterinarian, respectively. CONCLUSIONS: Reminder letters for cancer screening services were rarely utilized in this study population. Receipt of a reminder letter was associated with greater compliance with current screening recommendations.     

Non-responders to a postal questionnaire on respiratory symptoms and diseases

Only few data have been published about non-responders in epidemiological studies on respiratory diseases. The aim of this study was to examine the characteristics of the non-responders and the reasons for non-response in a survey of respiratory health. All 9132 subjects, born 1925–1926, 1940–1941, 1955–1956 and 1970–1971 and living in eight representative areas in Norrbotten, Sweden, were invited to a prevalence study on asthma, chronic bronchitis and respiratory symptoms. The response rate was 85%. A sample of the non-responders from the cross-sectional postal questionnaire study was contacted by telephone and interviewed using the same questionnaire as had been used in the postal survey. Of the 1397 non-responders a stratified sample of 182 subjects were selected for this study and 144 agreed to participate. The response rate was increasing by increasing age. The main reason for non-response was that the subjects had forgotten to mail the questionnaire, lack of interest or lack of time. There were significantly higher proportions of current smokers and manual workers among the non-responders. The prevalence rates of wheezing, long-standing cough, sputum production, attacks of breathlessness, asthma and use of asthma medicines were significantly higher among the non-responders compared with the responders according both univariate and multivariate logistic regression analyses, in which the influences of age, sex, smoking habits, socio-economic group and area of domicile were taken into account. The prevalence of respiratory symptoms and diseases was slightly underestimated in the postal survey.     

Telephone reminders are a cost effective way to improve responses in postal health surveys

STUDY OBJECTIVE: To assess the effectiveness of a telephone reminder in increasing responses to postal surveys and to calculate the differential costs per completed questionnaire. DESIGN: Randomised controlled trial. SETTING: Australian university and rehabilitation medicine practice. PARTICIPANTS: The trial was conducted in 1999 among the 143 non-respondents to a questionnaire about work related neck and upper body disorders. The questionnaire was sent to two Australian female samples: 200 office workers (Sample A) and 92 former rehabilitation medicine patients (Sample B). A reminder letter, another copy of the questionnaire and a final letter were sent at two week intervals. Half of the non-respondents within each sample were randomly selected to receive a telephone reminder just after the second mailout of the questionnaire. All direct costs were calculated. MAIN RESULTS: Responses were significantly higher among those who received the telephone reminder intervention (relative risk 2.54, 95% confidence intervals 1.43 to 4.52). Analysed by intention to phone, 47% of non-respondents in Sample A and 38% in Sample B returned a complete questionnaire after the intervention, compared with 21% and 10%, respectively, in the control groups. For the 112 women (combined samples) who returned completed questionnaires before randomisation, the average cost per respondent was AUD14. There was a higher total cost for the intervention groups (AUD851 versus AUD386 for controls), but the significantly higher number of additional completed responses (31 versus 12) resulted in a 15% lower marginal cost per completed questionnaire in those groups. CONCLUSION: Telephone reminders are cost effective in improving responses to postal surveys.