The sensitivity of forensic tests for rape

The objective of this study is to provide an overview of the types of forensic evidence gathered during clinical examinations in cases of sexual assault, and to review the literature regarding the sensitivity of individual procedures. The methodology involved a computerized literature search of the MEDLINE, PsycINFO, Cinahl and HealthStar databases from 1992 to 1996, and a secondary search involving consultation with local facilities and manual searching of reference lists. Based on our review, the chance of finding positive evidence is largely time-dependent, particularly regarding sperm and seminal products, which are weighted most heavily in rape investigations. The best chance of recovering seminal evidence is most frequently stated as being less than 50%, with far lower chances after 24 hours. Specific tests such as pubic hair combing would not be expected to yield evidence in more than 4% of cases. That test, while of low sensitivity, is at least not as invasive as some of the others. More invasive tests, such as sampling from the rectal cavity, yield positive sperm findings in fewer than 2% of cases. The importance of ensuring that those working in the field of sexual assault understand that no positive finding on forensic tests does not mean that no attack occurred is highlighted. Medico-legal implications are discussed and suggestions for future research initiatives are highlighted.