Watterson estimator

In population genetics, the Watterson estimator is a method for describing the genetic diversity in a population. It is estimated by counting the number of polymorphic sites. It is a measure of the "population mutation rate" (the product of the effective population size and the neutral mutation rate) from the observed nucleotide diversity of a population. ${\displaystyle \theta =4N_{e}\mu }$, where ${\displaystyle N_{e}}$ is the effective population size and ${\displaystyle \mu }$ is the per-generation mutation rate of the population of interest (Watterson (1975) ). The assumptions made are that there is a sample of ${\displaystyle n}$ haploid individuals from the population of interest, that there are infinitely many sites capable of varying (so that mutations never overlay or reverse one another), and that ${\displaystyle n\ll N_{e}}$. Because the number of segregating sites counted will increase with the number of sequences looked at, the correction factor ${\displaystyle a_{n}}$ is used.

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