Social desirability bias in family planning studies: a neglected problem

Abstract

Studies on family planning methods traditionally have relied on self-reports of unknown validity and reproducibility. Social desirability bias, a type of information bias, occurs when study participants respond inaccurately — but in ways that will be viewed favorably by others. Several lines of evidence reveal that this bias can be powerful in sexual matters, including reports of coitus, use of contraceptives and induced abortion. For example, studies using vaginal prostate-specific antigen testing reveal underreporting of unprotected coitus and overreporting of barrier contraceptive use. Medication Event Monitoring System studies, which electronically record the time of pill dispensing from a bottle or pack, indicate widespread exaggeration of adherence to pill-taking regimens, including oral contraceptives. Comparisons of provider data and self-reports of induced abortions reveal extensive underreporting of induced abortion. Reliance on self-reported data underestimates contraceptive efficacy. Although techniques to minimize this bias exist, they are infrequently used in family planning studies. Greater skepticism about self-reports and more objective means of documenting coitus and contraceptive use are needed if contraceptive efficacy is to be accurately measured.

Introduction

Studies to estimate efficacy of family planning methods traditionally have relied on self-reports of coitus and contraceptive use; these reports, however, are of unknown validity and reproducibility. Social desirability bias, a type of information bias, occurs when respondents distort the truth in ways that will be viewed favorably by others [1]. Although this bias has received considerable attention in the sexually transmitted disease (STD) and HIV/AIDS literature, it has been neglected in the field of family planning [1], [2], [3]. In this commentary, we will show how social desirability bias results in an underestimation of the efficacy of contraceptives and the frequency of induced abortion.

Social desirability bias is widespread in medical and psychological research. Its extent depends on whether the respondent has embarrassing information to disclose and on how the sensitive questions are framed. Examples of underreporting of socially undesirable behaviors include illicit drug use (as verified by urine and hair analysis) [4], dietary fat intake by women (as judged by a statistical model) [5], total nutrient intake (comparing 7-day diet recalls with 24-h recalls) [6], failure to use insecticide-treated bed nets for children (comparing health care facility reports and household surveys) [7] and number of sexual partners [informal confidential voting interviews vs. face-to-face (FTF) interviews] [8].

Efficacy studies of family planning methods typically request information from participants about coitus and use of contraceptives. The usual methods are interviews or daily diaries maintained by the participants. This reliance on self-reports may be inappropriate, given the documented deficiencies in such reports in the STD and HIV/AIDS literature [9], [10], [11], [12], [13]. The problem of social desirability bias has not been adequately considered in the family planning literature, and, indeed, some have even dismissed it as a concern [14].

Several lines of evidence suggest that self-reports of coitus and use of family planning methods are not accurate. The first is the use of prostate-specific antigen (PSA) testing of the vagina to corroborate reports of coitus and barrier contraceptive use. The second is the disparity between patient reports of pill-taking and computer records of medication dispensing. The third is the well-documented underreporting of induced abortion. All of these converge on the conclusion that self-reports are often not credible.