Man, woman, and child
|The man may be the father and the woman may be the mother but we
are not to assume either one. Some genetic tests are performed and we
do the following analyses
How does the reasoning go? Or, is it necessary to make a third,
separate analysis a motherless paternity calculation comparing just
the man and the child?
- The woman is compared with the child as a
fatherless maternity test,
and the likelihood ratio is very high; she
looks like a mother to this child.
- The man, woman, and child are compared as
an ordinary paternity trio and the likelihood ratio is very low,
perhaps even zero. He does not look like the father if she is the
- Can we therefore conclude that he is
unlikely to be the father regardless of who might be the mother?
No, the conclusion doesn't necessarily follow. Consider the
following simple example:
- Man and woman are both QQ, where Q is rare.
- Child is PQ.
likelihood ratio for the woman alone
is 1/2q, a large number.
- The likelihood ratio for the trio is 0 very low.
- But you cannot predict thereby that the likelihood ratio for
the man will be low, because in this case it is 1/2q, not low.
Comments? Questions? Disputes?
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