The AI is useful to help settle the question of paternity when the DNA profiles are consistent with paternity at nearly all loci but “inconsistent” at a few loci. In that situation it may be either that
Theory or data may suggest an expected frequency spectrum, which can then be regarded as prior probabilities for the frequencies of allelic or haplo-types. Such a prior can be used along with Bayes’ theorem and a sample reference database of allelic types, to infer allele probabilities.
Brenner’s Law is a statement about the frequency spectrum for forensic STR loci.
The framework we consider is trying to judge between two possible hypotheses. A typical pair of hypotheses would be:
Evidence, i.e. information or data such as DNA profiles, may be better explained by one of the hypotheses than by the other.
Implication: Since the term
“ground truth” of a mixture
is a description of mixture substance,
it has limited relevance to
mixture data.
In particular, analysis by Mixture Solution
or other software that (for example) estimates number of contributors,
is not right or wrong according to whether it agrees with ground truth.
It’s a tortuous route from the moment DNA is deposited as
mixture substance to the final version of
mixture data.
It’s not a paradox that the best possible analysis of mixture data,
the most correct analysis, sometimes differs from the ground truth about something else.
When the object of the identification is humanitarian it is typically virtually the case that decision making is deferred to the scientists. In that case, two useful concepts are:
Example: Suppose n=1000 missing, LR=80000 supporting corpse V to be missing person Jim Jones, and that the agreed policy is to declare identification when the probability is at least 99.9%. Using the baseline prior probability of 1/1000, the posterior probability is only 98.8% and the threshold is not achieved. A prior of about 1/81, 12-fold larger than the baseline prior, is the requisite prior to obtain 99.9%.
Maybe there is some quite useful non-DNA evidence supporting the ID, for example the body V shares a surgical scar approximately like Jim Jones is known to have had, and the stature is about right as well. It would be hard to estimate the exact evidential value of those coincidences, but we don’t have to. It is sufficient to judge that they are worth at least LR=12, the shortfall from the DNA evidence.
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