Assessing non-response to a mailed health survey including self-collection of biological material

Background: Collection of biological material via mailed health surveys is an emerging trend. This study was conducted to assess non-response bias in a study of sexually transmitted infection utilizing self-collected, home-obtained specimens. Methods: Data from a nationwide administrative database on health care utilization together with data from a research study were used. The research study was an outreach screening programme including home-obtained, participant-collected, mail-delivered testing for Chlamydia trachomatis. A random sample of 1690 persons aged 18-35 years from the population registry was selected. Study materials (specimen collection kit, informed consent, questionnaire) were mailed in three waves. Results: The first mailing yielded a response rate of 18.5% (n = 259), the second 10.1% (n = 141) and the third 11.4% (n = 160). Women were more likely to respond than men, and responders were less likely to have had medical care in the past year and more likely to have had a prior sexually transmitted infection than non-responders. Chlamydia trachomatis infection rates tended to be higher in early responders. Late responders appeared more like non-responders in terms of demographic factors, health care utilization patterns and potential disease status. Conclusion: Non-response in a health survey including biological material self-collection warrants research as it may differ from non-response in general health questionnaires.