INTRODUCTION: Whether or not third mailings are appropriate or worthwhile in postal epidemiological studies has not been thoroughly investigated and requires examination.
METHODS: A self-completion postal questionnaire of 2184 individuals was conducted in 2000. The socio-demographic and health characteristics of four groups of individuals (first mailing respondents, second mailing respondents, third mailing respondents and non-respondents) were compared.
RESULTS: Some significant differences between the groups were found, however, the inclusion of respondents to the third mailing did not significantly change the overall characteristics of respondents compared to non-respondents.
DISCUSSION: When differences do exist between respondents and non-respondents, our results suggest that a third mailing is unlikely to remove many of these differences. The study supports our previous suggestion that the effort and resources expended in carrying out a third mailing may not be justified.