# Y-DNA Match Determination

We keep encountering new and different ways of determining whether a match
exists between two sets of Y-DNA results (i.e., two men); some strike us as
bizarre. This page will attempt to catalogue and evaluate the methods we've
found as to their effectiveness and efficiency.

Perhaps, the best first step is to define what we mean by the term "match".

Note that this definition is not specific to Y-DNA STR testing, though that will be our focus
here. It allows us to re-frame the question into "Does the similarity of the sets of results allow us
to say with confidence that these men share a common male ancestor within
genealogic time?"

The best method for determining a Y-DNA match proceeds directly from the
definition and uses what is known about mutation frequencies of STR
markers. It relies on direct comparison of the two haplotypes as measured by
allele values of markers tested in common.

The calculations utilize the binomial probability theorem, a complicated formula. Alternatives
to manually calculating the probabilities include: