LIKELIHOOD RATIOS FOR MIXED STAINS WHEN THE NUMBER OF DONORS CANNOT BE AGREED

Suppose that part of the prosecution's evidence e in some crime case i s analysis of a blood stain, and that the traits E discovered in the s tain suggest multiple donors. Then the prosecution will probably alleg e some specific inculpatory hypothesis Ho about the sources of the sta in, and P {E \ H-0} can be calculated. It is desirable to use this as the numerator of a likelihood ratio. However, in general the obvious d enominator P {E\ similar to H-0} cannot be calculated, so unless the d efense is sufficiently obliging as to stipulate to a specific choice a mong the potentially infinite number of more or less exculpatory alter native hypotheses, the desired likelihood ratio can't be evaluated. We show that nonetheless, in most cases there is an adequate inequality.