NCJ Number
75885
Journal
Journal of the Forensic Science Society Volume: 20 Issue: 4 Dated: (October 1980) Pages: 271-282
Date Published
1980
Length
12 pages
Annotation
In this British study, determinations of time since intercourse (TSI), important in sexual crime cases, were made using extracts from vaginal swabs. However, the significance of uneven distribution of semen in the vagina was not assessed.
Abstract
The study was based on the fact that the initially high acid phosphatase level found in the vagina immediately after intercourse would gradually fall over a period of 2 or 3 days to reach that normally shown by vaginal secretion. The study sought to rationalize and improve the acid phosphatase test by measuring the acid phosphatase activity accurately by means of an auto-analyzer and by compensating for the varying quantity of secretion absorbed by cotton swabs by measuring the ultraviolet asorption at 270nm of the swab extracts. A total of 283 vaginal swabs, dried at room temperature, were collected from volunteer donors. Plots of coital time log (AP/UV270) were constructed and the data used to assess how useful such a technique would be for estimating unknown times of intercourse. The usefulness of the data was tested by means of a declared blind trial. A statistical presentation of results was also devised, which is consolidated by more data, would aid the scientist to assess the evidential value of swab analysis. The results indicated that AP/UV ratios would adequately compensate for intra-individual variation in the amount of secretion absorbed, but there was no evidence on the significance of possibly uneven distribution of semen in the vagina, especially immediately after intercourse. This should be known before a swab-taking procedure could be recommended. Perhaps a component of vaginal secretion whose concentration would be inversely proportional to the rate of flow should be sought and used as a factor to reduce this particular variable. A blind trial and an alternative statistical treatment of the data (with an example) are described. Statistical data and 16 references are included.