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Collecting saliva samples by mail.

Collecting saliva samples by mail can serve numerous purposes in epidemiologic research. The objectives of this study were to assess what proportion of participants in a mail survey would provide a saliva sample and whether incentives could improve participation. In 1995, 2,994 students, faculty, and staff members of Geneva University, Geneva, Switzerland, were randomized to receive, together with a mailed questionnaire about smoking, a saliva vial, a ballpoint pen, the offer of a lottery, or any combination of these. After one mailing and a reminder letter, response rates were 52% among those who had been requested to provide saliva and 63% among controls (p < 0.001). In the former group, most respondents (98%) provided a saliva sample. Incentives improved participation only among those who were asked to provide saliva (lottery: +11% response, p = 0.003; pen: +6% response, p = 0.1). The final participation, after up to three reminders, was 76% overall. The authors conclude that while the collection of saliva samples by mail is feasible it tends to decrease response rates.

Adolescent↗

Improvement in cumulative response rates following implementation of a financial incentive.

Risk estimates arising from case-control studies can be unreliable if the level of response to mailed questionnaires is inadequate. Several studies have reported improved early response rates to mailed questionnaires following the implementation of financial incentives. Improvements in cumulative response rates at the completion of the follow-up period, however, have not been as pronounced. A financial incentive of $5.00 was implemented among control subjects in a large population-based case-control study of Ontario, Canada, women. Required follow-up time and effort were decreased for the controls who received the incentive compared with those who did not. More importantly, cumulative response rates after more than 20 weeks were 20 percent higher among controls who received the incentive.

Adult↗

Increasing response rates for mailed surveys of Medicaid clients and other low-income populations.

Mailing surveys to low-income populations is often avoided because of concern about low response rates. In this study, the authors used a mailed survey of a low-income population to test whether $1.00 or $2.00 cash-response incentives were worth the expense and whether 2-day priority mail ($2.90 postage) would yield a sufficiently higher response rate than certified mail ($1.52 postage) to justify its cost. In 1994, 2,243 randomly selected families in subsidized health care programs in Pierce County, Washington, were randomly sent no incentive, $1.00, or $2.00 in the first of three mailings. For the third mailing, nonrespondents were randomly assigned to receive either certified or 2-day priority mail. After 4 weeks, the response rates were 36.7%, 48.1%, and 50.3% for the no-incentive, $1.00, and $2.00 groups, respectively. After three mailings, the cost per response was the lowest for the group that received $1.00. The response rate for the certified mailing (28.1%) was significantly higher than the rate for the more expensive priority mailing (21.7%). No incentive-related bias was detected. The authors concluded that the most efficient protocol for this low-income population was to use a $1.00 incentive in the first mailing and a certified third mailing.

Aged↗

Mail survey response by smoking status.

A detailed smoking history questionnaire was mailed to a series of 1987 white male veterans participating in the Normative Aging Study of the Veterans' Administration Outpatient Clinic in Boston, Mass. Response time from mailing date to return date was determined and then compared by various smoker categories. Although a total response rate of 96 percent was achieved after six months, the results showed that cigarette smoker response rates were considerably lower than the other smoker categories withing 30 days and within 60 days of the original mailing date. Cigarette smokers would therefore be under-represented if the data collection had ended within these spans of time; and even to some extent after six months had elapsed from time of original mailing. A relationship was also found between amounts of cigaretts smoked and rate of response with heavier smokers being slowest to respound. The implications of the findings with respect to cohort studies of smoking and heath are discussed.

Epidemiologic Methods↗

Nonresponse bias and early versus all responders in mail and telephone surveys.

Mail and telephone survey methods, with or without follow-up by other methods, are cost-effective alternatives to the conventional home interview approach. However, it has long been thought that they are especially susceptible to nonresponse bias. The study addressed this issue in the context of parallel mail and telephone health surveys carried out in Montreal. The mail strategy among 1,555 adults achieved 68.5% response and follow-up by telephone and home interview increased response to 80.9%. Respondents were adequately representative of the entire sample with respect to socioeconomic status, number of adults in household, and ethnic distribution. The 68.5% initial stage respondents were similar to all respondents on the above variables as well as on age, sex, education and reported health status. Odds ratios of smoking and respiratory symptoms hardly differed between initial stage and all respondents. The telephone survey among 1,595 adults achieved 72.7% response and follow-up by mail and personal interview increased response to 88.2%. Comparisons between respondents and the entire sample and between initial stage respondents and all respondents gave similar results to those found in the mail strategy, although there was some change in a symptom-smoking odds ratio from the initial stage respondents to all respondents. In both survey strategies, there was no evidence of substantial nonresponse bias and estimates of morbidity and health care would not have differed much if the fieldwork had stopped at the initial mail or telephone stage.

Adolescent↗

Quality of response in different population groups in mail and telephone surveys.

Mail and telephone survey methods, with follow-up by other methods, can provide high response rates. However, it is not clear whether different population groups provide responses of different quality, thus creating risk of biased comparisons. A closely related problem is whether proxy response adequately substitutes for self-response. This study addressed these issues in the context of parallel mail and telephone health surveys carried out in Montreal. In the telephone survey, proxy respondents provided lower estimates of morbidity and health care utilization than self-respondents; in the mail survey, there was no difference between proxy and self-response. Response validity was assessed by comparing reported physician visits with those recorded by the government-run universal health insurance plan. In general, mail responses were more valid than telephone responses. In both methods, there were suggestive but not persuasive differences in validity among sociodemographic subgroups. In both methods, those reporting illness or medication use had less underreporting of physician visits than those not reporting such things.

Adolescent↗

A comparison of costs and data quality of three health survey methods: mail, telephone and personal home interview.

Three survey modes--a self-administered mailed questionnaire, a telephone interview, and a home interview--were assessed for survey costs, adequacy of completion, test-retest reliability, validity of responses to medical questions and estimates of morbidity. Costs per household for each mode were $A42.75, $A74.33, and $71.89, respectively. Item omission was confined virtually to the mail mode and averaged 5.5% over 84 questions assessed, while telephone and home interview modes averaged 0.4% and 0.2%, respectively. "Don't knows" were virtually absent for all questions except those about precise details (names, places, etc.) of events occurring often 10-15 years before the survey; no mode differences were observed. The mail mode produced less reliable responses to questions about environmental exposure to hazardous chemicals or activities when considered question-by-question, but differences were not significant among modes when all questions were grouped. Reliability was high to medical questions and no mode differences were observed. Medical conditions which would require a medical diagnosis for subjects to be able to report them were more reliably answered than conditions described in broad or lay terms. Validity of answers to medical questions varied across modes and types of questions; underreporting of medical conditions was highest in the mail mode and was lowest for conditions requiring a diagnosis. Overreporting was lowest in the mail mode and highest for conditions requiring a diagnostic opinion.

2,4,5-Trichlorophenoxyacetic Acid↗

The use of a self-administered questionnaire to assess diet four years in the past.

The use of a mailed, self-administered, semiquantitative food frequency questionnaire to describe past dietary intake was evaluated in 1984 among a group of 150 Boston-area women who had completed four one-week diet records three to four years previously. Correlation coefficients comparing calorie-adjusted nutrient intakes computed from the questionnaire with those obtained from a compressed version of the questionnaire completed during diet record keeping ranged from 0.44 for total carbohydrate to 0.62 for vitamin C including supplements. Coefficients comparing calorie-adjusted nutrient intakes measured by questionnaire with those assessed by the diet records completed three to four years previously ranged from 0.28 for iron without supplements to 0.61 for total carbohydrate. An evaluation of the incremental contribution provided by several open-ended sections of the questionnaire to the estimation of nutrient intake suggested that in this population most of these items might be eliminated without material loss of information. These findings demonstrate that useful estimates of nutrient intake several years previously can be obtained by a relatively inexpensive, mailed, self-administered questionnaire.

Adult↗

Effectiveness of various mailing strategies among nonrespondents in a prospective cohort study.

Measures of association in prospective studies can be distorted by incomplete follow-up. Various mailing strategies were used to contact 12,233 cohort members of the Health Professionals Follow-up Study who had not responded to three successive bulk-rate mailings. Response rates were highest, 79.5% overall, from participants who were sent a certified mailing in phase 1 (63.2%), followed by a repeat certified mailing to nonrespondents (44.3%). Although altering the physical appearance of the envelope and using other postal rates were tested, certified mail was the most effective approach for reaching study members who were nonrespondents to a mailed questionnaire.

Adult↗

Assessment of the prevalence and risk factors for human immunodeficiency virus type 1 (HIV-1) infection among college students using three survey methods.

To evaluate the seroprevalence and risk factors for human immunodeficiency virus type 1 (HIV-1) infection among undergraduate college students, the authors simultaneously conducted three types of surveillance on a large university campus (27,902 undergraduates) in the Baltimore-Washington metropolitan area: a voluntary HIV-1 serosurvey with a linked risk assessment questionnaire (n = 3,394), a blinded serosurvey using blood specimens collected for routine purposes in the Student Health Center (n = 1,829), and a random sample risk assessment and case identification mail survey (n = 1,017 respondents of 3,000 solicited). The proportion of students belonging to a known risk group (a homosexual or bisexual man, intravenous drug user, or a sexual partner of a bisexual man, an HIV-1-infected person, a female prostitute, or an intravenous drug user) was 5.9% in the mail survey and 8.8% in the voluntary serosurvey. Whereas no infections were detected in the blinded serosurvey, two infected persons were identified in the mail survey (0.2%) and two in the voluntary serosurvey (0.06%), all among high-risk persons. Although derived from independent samples and subject to different biases, these three survey methods yielded a consistent pattern of HIV-1 epidemiology on this campus, whereby the overall prevalence of infection was low and confined to members of high-risk groups, despite the common occurrence of behaviors that might facilitate sexual transmission of HIV-1 among many other students.

Data Collection↗

The effect of two mailing strategies on the response to a survey of physicians.

In 1989, the authors tested the effectiveness of two response-enhancing techniques, a postage stamped or franked return envelope and a prenotification letter, in a survey of pregnancy among 10,047 resident physicians in the United States. The techniques were randomly assigned using a factorial design. No significant interactions were observed between the techniques. After two mailings, those who received a stamped return envelope had a response of 71.2%, compared with 68.2% for those who received a franked return envelope (95% confidence interval 1.3-4.9%). Men who received the stamped envelope had a 5.9% greater response than those who received the franked envelope (p less than 0.001), but the type of postage did not influence response among women (p = 0.84); this interaction was statistically significant (p = 0.006). Physicians who received a prenotification letter had a response of 69.0%, compared with 70.5% for those who did not receive the letter (95% confidence interval -3.3 to 0.2%). The authors conclude that seemingly minor changes in survey design could have saved from 12% to 19% of the total cost of the study.

Confidence Intervals↗

Occupational injuries: comparing the rates of male and female postal workers.

To compare the injury rates of male and female postal workers, the authors reanalyzed data on a cohort of 2,337 new postal employees in Boston, Massachusetts, hired between 1986 and 1989. The analysis controlled for potential confounding by age, race, smoking status, and drug use. Using Cox proportional hazards models with time-dependent variables, the authors found that, compared with men, women had an increased relative risk for occupational injuries in each of the three largest job classifications: letter carrier, letter-sorting machine clerk, and mail handler. The relative risks were not constant over time. For letter carriers and letter-sorting machine clerks, the increased risks for women were noted only during the first year of employment (relative risk (RR) = 1.93, 95% confidence interval (CI) 1.40-2.67) and RR = 2.60, 95% CI 1.31-5.15, respectively). For mail handlers, the increased risks for women were noted only after the first year of employment (RR = 2.13, 95% CI 1.09-4.15). As the percentage of women in the work force increases, these results suggest the need for further research to define sex-specific injury risks and to devise prevention strategies.

Accidents, Occupational↗

Using geographic information systems to assess risk for elevated blood lead levels in children.

OBJECTIVES: Targeted screening for childhood lead poisoning depends on assessment of risk factors including housing age. Using a geographic information system (GIS), we aim to determine high-risk regions in Charleston County, South Carolina, to assist public health officials in developing targeted lead-screening. METHODS: Properties built before 1978 were geocoded (assigned latitude and longitude coordinates) from tax assessor data. Addresses of Charleston County children who have been screened for lead poisoning were also geocoded. Locations of all housing, lead poisoning cases, and negative screens were created as separate map layers. Prevalence ratios of lead poisoning cases were calculated, as were relative risks for each category of housing. RESULTS: Maps of Charleston County were produced showing the location of old housing, where screening took place, and where cases were found. One thousand forty-four cases were identified. Twenty percent of children living in pre-1950 homes had elevated blood lead levels (EBLL). Children living in pre-1950 housing were 3.9 times more likely to have an EBLL than children living in post-1977 housing. There was no difference in risk of living in a 1950-1977 home vs. a post-1977 home. A large number of cases were also found in an area of newer houses, but near a potential point source. Eighty-two percent of all screens were from children in post-1977 homes. CONCLUSIONS: Children living in pre-1950 housing were at higher risk for lead poisoning. GIS is useful in identifying areas of risk and unexpected clustering from potential point sources and may be useful for public health officials in developing targeted screening programs.

Child↗

Monitoring socioeconomic inequalities in sexually transmitted infections, tuberculosis, and violence: geocoding and choice of area-based socioeconomic measures--the public health disparities geocoding project (US).

OBJECTIVES: To determine which area-based socioeconomic measures, at which level of geography, are suitable for monitoring socioeconomic inequalities in sexually transmitted infections (STIs), tuberculosis (TB), and violence in the United States. METHODS: Cross-sectional analysis of public health surveillance data, geocoded and linked to area-based socioeconomic measures generated from 1990 census tract, block group, and ZIP Code data. We included all incident cases among residents of either Massachusetts (MA; 1990 population = 6016425) or Rhode Island (RI; 1990 population = 1003464) for: STIs (MA: 1994-1998, n = 26535 chlamydia, 7464 gonorrhea, 2619 syphilis; RI: 1994-1996, n = 4473 chlamydia, 1256 gonorrhea, 305 syphilis); TB (MA: 1993-1998, n = 1793; RI: 1985-1994, n = 576), and non-fatal weapons related injuries (MA: 1995-1997, n = 6628). RESULTS: Analyses indicated that: (a). block group and tract socioeconomic measures performed similarly within and across both states, with results more variable for the ZIP Code level measures; (b). measures of economic deprivation consistently detected the steepest socioeconomic gradients, considered across all outcomes (incidence rate ratios on the order of 10 or higher for syphilis, gonorrhea, and non-fatal intentional weapons-related injuries, and 7 or higher for chlamydia and TB); and (c). results were similar for categories generated by quintiles and by a priori categorical cut-points. CONCLUSIONS: Supplementing U.S. public health surveillance systems with census tract or block group area-based socioeconomic measures of economic deprivation could greatly enhance monitoring and analysis of social inequalities in health in the United States.

Adolescent↗