Impact of different privacy conditions and incentives on survey response rate, participant representativeness, and disclosure of sensitive information: A randomized controlled trial

Maureen Murdoch, Alisha Baines Simon, Melissa Anderson Polusny, Ann Kay Bangerter, Joseph Patrick Grill, Siamak Noorbaloochi, Melissa Ruth Partin

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43 Scopus citations


Background: Anonymous survey methods appear to promote greater disclosure of sensitive or stigmatizing information compared to non-anonymous methods. Higher disclosure rates have traditionally been interpreted as being more accurate than lower rates. We examined the impact of 3 increasingly private mailed survey conditions - ranging from potentially identifiable to completely anonymous - on survey response and on respondents' representativeness of the underlying sampling frame, completeness in answering sensitive survey items, and disclosure of sensitive information. We also examined the impact of 2 incentives ($10 versus $20) on these outcomes. Methods. A 3X2 factorial, randomized controlled trial of 324 representatively selected, male Gulf War I era veterans who had applied for United States Department of Veterans Affairs (VA) disability benefits. Men were asked about past sexual assault experiences, childhood abuse, combat, other traumas, mental health symptoms, and sexual orientation. We used a novel technique, the pre-merged questionnaire, to link anonymous responses to administrative data. Results: Response rates ranged from 56.0% to 63.3% across privacy conditions (p = 0.49) and from 52.8% to 68.1% across incentives (p = 0.007). Respondents' characteristics differed by privacy and by incentive assignments, with completely anonymous respondents and $20 respondents appearing least different from their non-respondent counterparts. Survey completeness did not differ by privacy or by incentive. No clear pattern of disclosing sensitive information by privacy condition or by incentive emerged. For example, although all respondents came from the same sampling frame, estimates of sexual abuse ranged from 13.6% to 33.3% across privacy conditions, with the highest estimate coming from the intermediate privacy condition (p = 0.007). Conclusion: Greater privacy and larger incentives do not necessarily result in higher disclosure rates of sensitive information than lesser privacy and lower incentives. Furthermore, disclosure of sensitive or stigmatizing information under differing privacy conditions may have less to do with promoting or impeding participants' "honesty" or "accuracy" than with selectively recruiting or attracting subpopulations that are higher or lower in such experiences. Pre-merged questionnaires bypassed many historical limitations of anonymous surveys and hold promise for exploring non-response issues in future research.

Original languageEnglish (US)
Article number90
JournalBMC Medical Research Methodology
Issue number1
StatePublished - Jul 16 2014

Bibliographical note

Funding Information:
The Center for Chronic Disease Outcomes Research is a VA Health Services Research and Development (HSR&D) Service Center of Excellence (Center grant #HFP 98-001). This study was supported by grant #GWI 04-352 from VA HSR&D service. The funding agency had no role in the design, data collection, analysis, data interpretation, manuscript writing, or decision to submit the manuscript.


  • Anonymity
  • Confidentiality
  • Non-response bias
  • Participation bias
  • Patient surveys
  • Randomized trial


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