Fano factor

In statistics, the Fano factor, like the coefficient of variation, is a measure of the dispersion of a probability distribution of a Fano noise. It is named after Ugo Fano, an Italian American physicist.

The Fano factor is defined as

where ${\displaystyle \sigma _{W}^{2}}$ is the variance and ${\displaystyle \mu _{W}}$ is the mean of a random process in some time window W. The Fano factor can be viewed as a kind of noise-to-signal ratio; it is a measure of the reliability with which the random variable could be estimated from a time window that on average contains several random events.

For a Poisson process, the variance in the count equals the mean count, so F = 1 (normalization).

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