MATCH PROBABILITY

• Jurisdiction: Australia

MATCH PROBABILITY

Overview ....................................................................................................... [80A.400]

Can we ever be certain that the suspect is the source of the DNA at the crime scene? ............................................................................................ [80A.420]

If alleles are not unique, are whole profiles unique?.................................... [80A.440]

Is DNA typing different from other comparative forensic techniques in this respect? .................................................................................................... [80A.460]

[80A.400] Overview

Consider the situation where a suspect has a DNA profile that matches the profile of biological material associated with a crime. DNA statistics can be used to estimate the likelihood that a second person from some population may possess the same profile. This is termed the match probability.

Multi-locus DNA profiles containing information from nine loci have not been found to occur more than once in large collections of profiles: Weir (2004). Therefore, we would make an informed guess that it is highly unlikely that a second person would have the same DNA profile as the suspect. This becomes even more unlikely as the number of loci analysed increases.

If this could be shown to be true of our particular crime scene material, it would provide very strong support for the opposing view, namely, that the DNA came from the suspect, and very little support for the view that it came from a person other than the suspect.

Note that the...