THE FALLIBILITY OF DIAGNOSTIC-TESTS FOR SEXUALLY-TRANSMITTED DISEASES- THE IMPACT ON BEHAVIORAL AND EPIDEMIOLOGIC STUDIES

Objectives: Analysis of sexually transmitted disease (STD) data to ide ntify specific behaviors and risk factors often fails to take into acc ount the misclassification of disease by a less than perfect diagnosti c test, The authors consider here how a diagnostic test's performance profile can introduce misclassification and thereby bias measures of a ssociation. Methods: The authors used hypothetical data relating to di agnostic tests for Chlamydia trachomatis infections and oral contracep tive use to determine odds ratio estimates given a range of sensitivit y, specificity, prevalence of infection, and sample size. Results: Low er specificity in a diagnostic test can result in an underestimation o f a risk factor's association with an infection, This bias is particul arly severe in low prevalence populations, Use of a diagnostic test wi th low specificity also will increase the sample size needed to demons trate the association and, thus, the cost of such surveys. Conclusions : Diagnostics tests for sexually transmitted diseases have less than p erfect sensitivity and specificity, which affects the validity of anal yses of factors associated with sexually transmitted diseases. Analyse s done using low prevalence populations and/or small sample sizes may underestimate the magnitude of effect in retrospective studies and cli nical trials of behavioral interventions aimed at reducing sexually tr ansmitted disease risk.