Sexually Transmitted Diseases:
Accounting for Failures May Improve Precision:Evidence Supporting Improved Validity of Self-Reported Condom Use
Crosby, Richard PhD*; Salazar, Laura F. PhD*; DiClemente, Ralph J. PhD†§∥; Yarber, William L. HSD‡¶#; Caliendo, Angela M. MD,PhD§; Staples-Horne, Michelle MD**
From the *College of Public Health, University of Kentucky, Lexington, Kentucky; †Rollins School of Public Health, Emory University, Atlanta, Georgia; ‡Rural Center for AIDS/STD Prevention at Indiana University, Bloomington, Indiana; §Emory University School of Medicine, Department of Pathology and Laboratory Medicine (Infectious Diseases), Atlanta, Georgia; ¶Emory University School of Medicine, Department of Pediatrics, Atlanta, Georgia; ∥Kinsey Institute for Research in Sex, Gender, and Reproduction, Bloomington, Indiana; #Applied Health Science and Gender Studies at Indiana University, Bloomington, Indiana; and the **Georgia Department of Juvenile Justice, Atlanta, Georgia
This research was supported by the Emory Center for AIDS Research (NIH/NIAID 2 P30 AI50409–04A1).
Correspondence: Richard Crosby, PhD, College of Public Health, University of Kentucky, 121 Washington Ave., Room 111C, Lexington, KY 40506-0003. E-mail: firstname.lastname@example.org.
Received for publication November 8, 2004, and accepted January 11, 2005.
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.
IN 1995, ZENILMAN AND colleagues demonstrated a lack of association between self-reported condom use and prevalence of biologically confirmed STDs.1 Since then, scholarly debate has ensued regarding the validity of self-reported condom use.2–5 Specifically, possible overreporting of condom use has been suspected as the most likely source of misclassification bias, i.e., falsely classifying study participants as “consistent” users. Indeed, this form of bias may account for lack of observed associations between condom use and STDs.6,7 A recent analysis also suggested that a misclassification bias may result from underdiagnosis of STDs.8 Such a bias would also account for lack of observed associations between condom use and STDs. Yet another explanation has been that condoms may not work,9 although a recent review suggests that the evidence for condom effectiveness is relatively strong.10
Without question, an imperative exists to empirically investigate the degree of protective value that condoms provide against STDs.11 The core question is, what level of protection is conferred by the consistent and correct use of condoms? Unfortunately, research has focused on improved measures of “consistent” condom use but has largely ignored the assessment of “correct” use.11–13 Given that incorrect use can lead to condom failure, it is clearly important to adjust self-reported measures of condom use by frequency of condom failures. As receptive partners in penile-vaginal sex, females may be particularly susceptible to STD-pathogen exposure when condoms break, slip off, or leak upon removal. Evidence from studies of young adult women suggests that these (and other) forms of condom failure may be common occurrences.14–19 Accordingly, the purpose of this study was to test a single hypothesis. We hypothesized that an “adjusted measure of condom use” (i.e., adjusted for condom failures) would produce improved accuracy in predicting biologically confirmed STDs among females. We chose to sample teens. To ensure that our sample of female teens was likely to be at risk of STD acquisition, we chose to conduct the study among adjudicated girls sentenced to short-term detention facilities (located in the Southern United States). Evidence suggests that this population experiences substantial risk for STD infection.20,21
Eight detention facilities located in Georgia formed the basis for a cross-sectional survey of adolescents. Georgia detention facilities house adolescents convicted of offenses ranging from truancy to homicide. Based on state restrictions, we were only allowed to recruit a convenience sample of teens. Between October of 2001 and July of 2003, research assistants came to the detention facilities once each week to recruit newly admitted teens. Two hundred eighty-three female teens were recruited for participation in the study. The study achieved an 82% participation rate. Teens were eligible if they were 14 to 18 years old, expressed willingness to participate, and (if <18 years old) had a parent who provided informed consent. The institutional review boards at Emory University and the State of Georgia’s Department of Juvenile Justice approved all study procedures.
Based on evidence from previous research,22 we used audio computer-assisted self-interviewing (A-CASI) to deliver the self-assessment as this mode has been shown to decrease reporting bias. To help facilitate accurate recall yet provide a window of time long enough to be representative of true health-risk behavior, a 2-month recall period was used when asking adolescents about their past condom use. To comply with the State Juvenile Justice Department’s request, compensation to study participants was not provided.
Teens provided a first-catch urine specimen for STD testing. Specimens were initially tested for Chlamydia trachomatis and Neisseria gonorrhoeae DNA by ligase chain reaction using the Abbott LCx Probe System23–25 (Abbott Laboratories, Abbot Park, IL). In 2003, this Abbot assay was discontinued and we began using the BDProbeTec ET Chlamydia trachomatis and Neisseria gonorrhoeae Amplified DNA assay (Becton Dickinson and Company, Sparks, MD).26
Only teens who reported having penile-vaginal sex in the past 2 months and using condoms at least once in this time period (n = 134) were eligible to complete a single-item assessing condom failure. Evidence suggests that females are indeed aware of events related to condom failure, even though the act of condom use may be primarily controlled by the male partner.14,15 Teens were asked how often (in the 2 months before being admitted to the detention center) they had a condom break, leak, or slip off the penis.
Teens were also asked how many times they had engaged in vaginal sex (again, the recall period was the 2 months before admission to detention) and how many of these times a condom was used. A standard (i.e., unadjusted) measure of unprotected vaginal sex (UVS) was created by subtracting the latter measure from the former. The value of using UVS as opposed to the percent of intercourse occasions that are condom-protected has been well established.11 To test the study hypothesis, we first reconstructed the measure of UVS. The single-item measure representing the number of condom failures in the past 2 months was subtracted from the value teens had provided in response to how many times a condom had been used. This “adjusted” variable was then subtracted from the value teens had provided representing their frequency of having vaginal sex. Because the “consistent and correct” use of condoms is the theoretical plausible protective behavior against STD acquisition, the corrected measure of UVS was dichotomized to compare consistent users to less-than-consistent users.
Contingency table analysis was used to determine whether added precision was gained by use of the adjusted measure of UVS. Specifically, prevalence ratios, their 95% confidence intervals, and respective P values were calculated for both the unadjusted and adjusted measures.
Characteristics of the Sample
Average age of the adolescents was 15.3 years (SD = 0.93). Nearly 40% identified as white and non-Hispanic, with 41.0% identifying as black and non-Hispanic, 5.2% as white and Hispanic, 10.4% as black and Hispanic, and the remainder identifying as members of other races. The mean number of previous detention sentences served by teens was 2.46 (SD = 3.7). The measure of condom failure (i.e., frequency of breakage, slippage, or leaking in the past 2 months) produced a range of 0 to 8. About 15% of the teens reported 2 or more problematic events. The mean number of failures was 1.0 (standard deviation = 1.6). The measure of UVS yielded a range of 0 to 50, with a mean of 3.41 unprotected sexual encounters (standard deviation = 8.1). Nearly one half (48.0%) of the teens reported consistent condom use (i.e., no acts of UVS).
Valid specimens were not provided by 9 of the 134 teens; thus, findings are based on n = 125. Of these, 21 tested positive for chlamydia and 4 tested positive for gonorrhea. Two teens tested positive for both STDs. Thus, 23 teens (18.4%) testing positive for 1 or both pathogens were compared to those testing negative for both.
Table 1displays the frequency counts observed in the 2 sets of contingency tables. The unadjusted measure of UVS 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. Thus, the study hypothesis was supported.
To the best of our knowledge, this is the first study to demonstrate improved precision in predicting biologically confirmed STDs based on an adjusted measure of UVS. The adjustment is important because it simply corrects the predictor variable for the occurrence of condom failure. Clearly, in populations where forms of condom failure are common, this adjustment can add to the rigor of studies designed to test condom effectiveness. Conversely, our findings suggest that uncorrected measures of UVS are inaccurate and therefore invalid in tests that assess condom effectiveness against STDs. That the finding only applies to females is important as they have “the most to lose” if a condom breaks, leaks, or slips off (given that each event places females in direct contact with semen but may add little risk of STD acquisition for the partly exposed male).
Findings are limited by at least 3 factors. First, the validity of the self-reported data cannot be established. Indeed, the fact that 7% of those using condoms consistently and correctly tested positive for an STD suggests the possibility that condom use was overreported. However, it should also be noted that teens may have acquired chlamydia or gonorrhea before the 2-month recall period. This is especially likely, given that the sample was composed of females (as females may be less likely than males to experience symptoms and therefore seek diagnosis and treatment). Second, the use of a convenience sample precludes generalization to other populations. Third, the small sample size limited the available statistical power. However, given that the hypothesis was supported, it is clear that statistical power was not a handicap to the study. Fourth, the assessment did not account for how often participants were exposed to sex with an infected partner. Finally, it should be noted that the findings simply provided support for an alternative hypothesis (i.e., that null associations between UVS and STDs can be accounted for by considering condom failures). Certainly, other alternative hypotheses could be conceived and tested in subsequent studies.
Findings from this exploratory study of female teens suggest that they may commonly experience various forms of condom failure. The findings demonstrate that studies of condom effectiveness should use an adjusted measure to enhance the precision and rigor of self-reported data pertaining to unprotected vaginal sex.
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