 |
 |
Over the past couple of months I have sent two messages to allstat suggesting that statisticians should show interest publicly in situations where considerations about simple probabilistic reasoning are mishandled with strong effects for individuals. Specifically, I have mentioned the relative frequencies which need to be considered on receiving a test result that one is HIV+ (*), and the judicial deliberations over the unfortunate Sally Clark who lost two children in circumstances which each appeared to be those of cot death. A third, and more greatly worrisome situation which has been concerning me has been the way in which, in criminal investigations, an enormously extreme surprise value is placed upon a DNA match, and the related pressure from some quarters to establish a 100% DNA database for forensic purposes. In this latter concern, I find that I have been overtaken by a radio program, broadcast yesterday (04-Jul-00); I heard most but not all of the program. This was on BBC Radio 4, in the series 'File on Four'. The programme dealt particularly with the number of codes possible in a particular type of DNA test (different tests deal with different 'numbers of points' of the DNA code sequence), and with whether code sequences from different individuals should be regarded as completely independent realisations of a statistical process (I paraphrase). It also dealt with non-statistical matters : the handling mistakes which can be made in applying DNA tests (and also fingerprint tests), the existence of considered unpublished reportage which would tend to undermine confidence in the uniqueness of a DNA test match outcome in practical forensic testing situations, and at least one case of successful appeal against a conviction based upon a DNA match where other forms of evidence showed that the alleged perpetrator could not have done the deed. File on Four is usually repeated on Sundays at 5 p.m., so I will be listening carefully on 09-July. If you find this stuff engaging and important then you too might wish to try and catch the repeat. PS: I wonder what proportion of allstat subscribers are Radio 4 listeners (but this is *not* a survey and *not* for reply to the list !). Norman Marsh %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%