A contribution to the discussion of probabilities and human hair comparisons

The paper by Gaudette and Keeping on 'An Attempt at Determining Probabilities in Human Scalp Hair Comparison' in the Journal of Forensic Sciences has provoked considerable controversy. This paper highlights two of the sources of the controversy and shows how the probability, 1/4500, quoted by Gaudette and Keeping should be treated with caution. The necessity of the use of a likelihood ratio statistic is described. It is suggested that the hair examination form resulting from the responses to the questionnaire recently distributed by the authors and also the discussions at Quantico should be used to facilitate the collection of the data which will be necessary to enable a likelihood ratio statistic to be estimated effectively.