Accounting for failures may improve precision: Evidence supporting improved validity of self-reported condom use

Objectives: To determine whether a measure of unprotected vaginal sex that is adjusted for condom failures would produce improved accuracy in predicting biologically confirmed STDs (chlamydia and gonorrhea) among female teens. Methods: Self-reported measures were collected using audio-computer-assisted self-interviewing. DNA amplification for the presence of Chlamydia trachomatis and Neisseria gonorrhoeae was conducted. Results: The unadjusted measure of unprotected vaginal sex was not significantly associated with biologically confirmed prevalence of STDs (prevalence ratio [PR] = 1.51; 95% CI = 0.71-3.21; P = 0.28). Alternatively, the adjusted measure achieved significance (PR = 3.59; 95% CI = 1.13-11.38; P = 0.014). More than one quarter (25.6%) of teens using condoms inconsistently and/or incorrectly tested positive for an STD compared to 7.1% among those reporting the consistent and correct use of condoms. Conclusion: Findings demonstrate that studies of condom effectiveness should use an adjusted measure of condom use to achieve precision and rigor.