Reply to Budowle, Ge, Chakraborty and Gill-King: use of prior odds for missing persons identifications

'What is the probability that these (unidentified) human remains are those of this missing person?' This question represents a typical example of Bayesian inference: an initial state of belief, expressed in terms of probabilities (or, alternatively odds) based on preliminary circumstantial information, can be revised through scientific data--in particular results of DNA analyses. As noted by Budowle et al. [1] in their commentary Use of prior odds for missing persons identifications, a reasoner's opinion after the consideration of genetic data is a function of the initial state of belief, so that there is some interest in inquiring about its foundations. Budowle et al. [1] further note that, besides considering the total number of missing persons, the field has particularly been silent about how to set initial probabilities. Their conclusion thus is that '[t]he forensic DNA community needs to develop guidelines for objectively computing prior odds' [[1], p. 1]. It is on this particular conclusion that we wish to comment here. In particular, we seek to argue that by considering a reasoner's belief state through the personalist interpretation of probability, the topic of prior odds (1) does not relate to objectivity, (2) is not a case for computation, and (3) does not require new guidelines.(1) The notion of objectivity is as widely used in scientific communications as it is undefined and, after all, illusionary [2]. In the particular context of forensic DNA analyses, Evett and Weir concisely expressed this as follows:'(. . .) we do not accept that DNA statistics are objective in the sense of being independent of human judgment. In spite of the often elegant mathematical arguments we have presented, we stress that the final statistical values depend wholly on the initial assumptions. The validity of these assumptions in any given case are a matter for expert opinion, so that we claim "objective science" can exist only within the framework of subjective judgment.' [[3]