DNA-profiling of stains in criminal cases: analysis of measurement errors and band-shift. Discussion of match criteria.

DNA-profiling was performed on approximately 600 stains (blood, semen/vaginal secretion, tissue samples and saliva) deriving from criminal investigations. The restriction enzyme was HinfI, and the VNTR (variable number of tandem repeats) probes were MS1, MS31, MS43a and YNH24. DNA-profiles were obtained from 60% of the stains, and matches were seen for 65% of the profiles. The measurement errors and the differences between corresponding fragment lengths of blood and stain profiles were analysed statistically. Distinct band-shifts were observed for approximately 65% of the profiles. For 50% of the profiles, the fragments derived from the stain fragments migrated faster than those from the blood sample, and for 15% of the profiles the stain fragments migrated slower. The difference between the migration distance of the stain and the blood fragments of a given pair of profiles increased with increasing migration distance, i.e. with decreasing fragment length. After correction for this slope the measurement errors were independent of the fragment length, and of the same order of size as for duplicate determinations of fragments from blood samples. The differences between the fragment lengths of corresponding profiles were highly correlated (rho = 0.8). Based on the statistical analysis, different match criteria are discussed and an ellipsoid accept-area is suggested.