 If it is difficult in practice to implement breeding programs and data analysis based on models that avoid reference to what is not observed, it is difficult to conceive such alternatives without the following prescriptive disambiguation. Here a restoration more than a reintegration can be entertained, that is, to insist on the distinction between variance in actual observable genotypes and genotypic variance (sometimes shortened to genetic variance, where variance is the statistical measure of variation in a given quantity). The latter term stems from breeders using the term genotypic value for the average value of a trait over all locations in which they raise or grow the genotype (in the sense of classes of individuals related by genealogy from a common ancestor or set of ancestors; see  section 3).  The variation among these genotypic values is, as shorthand, called the genotypic variance. In other words, the quantity derives from statistical analysis of variation among related and unrelated individuals in their phenotypes (in the sense of observed traits), not in their genotypes (in the sense of DNA). Not only does genotypic variance vary with the mix of genotypes and locations, its statistical estimation does not reference measurable genetic or environmental factors influencing the development of the traits. Unfortunately, it is common for researchers and commentators, including philosophers, to speak of genotypic or genetic variance in terms like the “contribution of genetic differences to observed differences among individuals” (Plomin et al. 1997: 83) as if variation in traits and variation in genotypes had some obvious relationship. The conflation may derive from quantitative genetic models being based on genotypes (in the sense of pairs of genes). But those are theoretical genotypes, unobserved and, as noted above, not essential to the analysis of trait variation. (To add to the potential for confusion, the technical term for the ratio of the genotypic variance to the total variance observed in the trait in question is Heritability, which has no relation to the existence of a connection between parent and offspring traits through transmission of genes [Taylor 2012].)