 So far we have introduced methods of measuring or calculating heritability that are somewhat intuitive. The problem is that these methods do not acknowledge all that is involved in the production of variation in the quantitative traits of organisms in a population. If we stick to the example of variation in height in a sample population of humans, we will discover that in most representative samples, heights are distributed more or less normally. The variance in height is defined as the average of the squared difference between each measured height and the mean height for the population. Variance in phenotype or phenotypic variance is symbolized as \(V_P\). (From here until the end of this section we adopt a specific strategy for presenting the equations used in spelling out heritability relations. We start out, with equation (1) below, by presenting the simplest version of the relevant equations. Simple equations such as (1) below are rarely ever satisfied but are routinely presented as adequate in elementary introductions to behavioral genetics. Subsequent equations in the sequence below render the relevant situation more accurately. Population geneticists endorse variants of (1′) below and do not endorse (1).)