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Open Access Research article

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

Maureen Murdoch123*, Alisha Baines Simon2, Melissa Anderson Polusny245, Ann Kay Bangerter2, Joseph Patrick Grill2, Siamak Noorbaloochi23 and Melissa Ruth Partin23

Author Affiliations

1 Section of General Internal Medicine, Minneapolis VA Medical Center, Minneapolis, MN, USA

2 Center for Chronic Disease Outcomes Research, Minneapolis VA Medical, One Veterans Drive, Minneapolis, MN 55417, USA

3 Department of Internal Medicine, University of Minnesota School of Medicine, Minneapolis, MN, USA

4 Departments of Psychiatry and Psychology, Minneapolis VA Medical Center, Minneapolis, MN, USA

5 Department of Psychiatry, University of Minnesota School of Medicine, Minneapolis, MN, USA

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BMC Medical Research Methodology 2014, 14:90  doi:10.1186/1471-2288-14-90

Published: 16 July 2014

Abstract

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.

Keywords:
Randomized trial; Patient surveys; Participation bias; Non-response bias; Anonymity; Confidentiality