Abstract
DNA profiling can be used to identify criminals through their DNA matching that left at the scene of a crime. The strength of the evidence supplied by a match in DNA profiles is given by the likelihood ratio. This, in turn, depends upon the probability that a match would be produced if the suspect is innocent. This probability could be strongly affected by the possibility of relatedness between the suspect and the true source of the scene-of-crime DNA profile. Methods are shown that allow for the possibility of such relatedness, arising either through population substructure or through a family relationship. Uncertainties about the likelihood ratio have been taken as grounds for the use of very conservative estimates of this quantity. The use of such conservative estimates can be shown to be neither necessary nor harmless.
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The author makes a good case for the use of likelihood ratios in presenting evidence. The author cites Nichols and Balding (1991) for the match probability involvingF ST , and readers will also need to consult Balding and Nichols (1994 and this volume) and Weir (1994). In light of current concern over laboratory errors or fraud, the author's comment that ‘Undetected and unsuspected human error or mischief is potentially a problem in almost all criminal cases, yet no convictions could follow if this possibility was consistently deemed to lead to reasonable doubt’ is well taken.
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Brookfield, J.F.Y. The effect of relatedness on likelihood ratios and the use of conservative estimates. Genetica 96, 13–19 (1995). https://doi.org/10.1007/BF01441147
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DOI: https://doi.org/10.1007/BF01441147