Doesanonymity increase responserateinpostal questionnaire surveysaboutsensitive subjects? A randomised trial

Studyobjective-The aimofthestudy was todetermine whethercomplete anonymity improvestheresponse ratesto a postal questionnaire. Design-Thestudyderived froma series of postalsurveys on AIDS knowledge conducted on sixdifferent datesin1986and 1987. Thesamplewas randomlydivided into two, each group beingsent the same questionnaire. One group was informed thatthereplies were anonymous, theother thattheywere not.The latter were sent reminders. Setting-Recipients ofthequestionnaires were drawn from the Southampton electoral rolis. Participants-300 peopleineachsurvey (total1800)were sent questionnaires, representing on eachoccasion a different 1:500 systematic sample. Results-Response ratewas 49%forthe anonymous questionnaires and51%forthe numbered questionnaires. Reminders boosted theresponseinthenumberedgroup to72%. Conclusions-There