No adequate criterion-standard for pharyngeal or rectal infections exists due to the probable, but poorly defined, low sensitivity of the current standard, culture. Fortunately, the 3 NAATs employ different C. trachomatis and N. gonorrhoeae molecular targets and methods of nucleic acid amplification. By including all 3 NAATs plus culture in the study, combinations of the results of culture and a NAAT or of two NAATs can be utilized to take advantage of the likely independence of testing errors among truly uninfected subjects to construct more satisfactory criterion standards for infection for the purpose of estimating and comparing their sensitivities and specificities. A secondary aim of the study will be to compare this methodological approach, utilizing a traditional statistical and clinical epidemiological approach, with alternative methods that have been more widely used but strongly criticized by statisticians and clinical epidemiologists and with newer methods designed to meet these criticisms and to be more efficient than the traditional statistical approaches.