5-4.9 Use of a family identifier.
If an individual uses his father's name as one of his own
identifiers, the coincidence value as a relative frequency does not really express the probability that
the names will agree by chance (and not represent the same individual). The chances that the
father's name (either given name or surname) or the mother's name refers to the same individual in
both records depends on the number of siblings the name might refer to instead. To approximate this
factor we could assume that the average number of siblings that a person might have is around six.
In this case the surname would be one-sixth as reliable as we would otherwise expect. Hence, we
have something like equations 5.6 and 5.7 for the surname field and the parents' name fields.
| aw = log2 [(r ÷ 6) c] | (5.6) |
| dw = log2 [(1 – [r ÷ 6]) ÷ (1 – c)] | (5.7) |
The siblings within a family are also prone to have different given names. Our sense is that
the reliability of the given name would increase when the names of the parents agree. Yet the fact
that some children may receive the names of previously (or shortly to be) deceased children
complicates this consideration. These are all factors judged manually by the genealogist on a case-by-case basis.
