1. A method of determining whether a sample matches a reference species, the method comprising: selecting N indices l 1, l 2,... l N of peaks in an indexed data set characterizing the reference species; selecting a first set of probabilities p 1, p 2,... p N that peaks will occur at indices l 1, l 2,... l N, respectively, of an indexed data set that characterizes the sample when the sample matches the reference species; selecting a second set of probabilities q 1, q 2,... q N that peaks will occur at indices l 1, l 2,... l N, respectively, of an indexed data set that characterizes the sample when the sample does not match the reference species; choosing a threshold K c ; obtaining an indexed observation data set x 1, x 2,... x N, where x j ∈&lcub;0, 1&rcub; and x j &equals;1 if and only if a peak is present in the sample at l j ; deciding that the sample matches the reference species if &lgr;&lE;K c where 33 λ = &Sum; 1 &leq; j &leq; N &it; &it; log &it; ( 1 - p j 1 - q j ) + &Sum; 1 &leq; j &leq; N &it; &it; x j &it; log &af; [ p j &it; ( 1 - q j ) q j &it; ( 1 - p j ) ] ; and deciding that the sample does not match the reference species if &lgr;>K c.