Variance

The variance of a trait measured in a population is the squared deviation from the mean.

If the mean is μ.

The expected variance is σ² = (x-μ)² where x is an individual data-point.

This can be estimated from a set of measurements as the average squared deviation by summing the individuals components and dividing by the total number of observations, n, as σ² = (1/n)∑(x_i-μ)², where x_i is each individual data-point as i goes from 1 to n.

Of the underlying factors that contribute to a traits variance are independent, then the total trait variance is a sum of the individual variance components. Example, ...