Direct measures of unsafe sex are difficult to obtain. Studies have used self-reported measures such as numbers and types of sex partners, frequency of sex acts, and condom use practices to try to measure unsafe sexual activity. However, discrepancies have been shown to exist between self-reports of sexual behavior and objective sexual risk behavior outcomes such as sexually transmitted infections.[1-3] Self-reported measures can also be unreliable, difficult to gather, and subject to errors in measurement, especially reporting and recall bias. This can especially be true for sexual activity, as sex is a highly charged issue which carries a stigma and can be heavily dependent on social norms.
As a consequence, it is easier to use proxy measures to represent sexual behavior. When addressing sexual risk behavior, the CDC points to promoting behaviors that can reduce risk for sexually transmitted diseases and teen pregnancy. Sexually transmitted infections can be a result of unsafe sexual activities including those used in self-reported measures such as condom practices and number of sexual partners. Teen births resulting from unintended pregnancies are an additional way to measure unsafe sex. Unintended pregnancy mainly results from the lack of, inconsistent, or incorrect use of effective contraceptive methods, and among women aged 15-19, more than 4 out of 5 pregnancies were unintended.
 DiClemente RJ, Sales JM, Danner F, Crosby RA. Association between sexually transmitted diseases and young adults' self-reported abstinence. Pediatrics. 2011;127(2):208-213.
 Zenilman JM, Weisman CS, Rompalo AM, Ellish N, Upchurch DM, Hook EW 3rd, Celentano D. Condom use to prevent incident STDs: The validity of self-reported condom use. Sex Transm Dis. 1995;22(1):15.
 Brown JL, Sales JM, DiClemente RJ, Salazar LF, Vanable PA, Carey MP, et al. Predicting Discordance Between Self-reports of Sexual Behavior and Incident Sexually Transmitted Infections with African American Female Adolescents: Results from a 4-city Study. AIDS Behav. 2012;1-10.
 Centers for Disease Control and Prevention Web Site: Sexual Risk Behavior: HIV, STD, & Pregnancy Prevention. Updated August 26, 2013. Accessed March 14, 2014.
 Centers for Disease Control and Prevention Web Site: Unintended Pregnancy Prevention. Updated February 12, 2013. Accessed March 14, 2014.