Dear Guinea-pig lovers,
Heritability is defined on the basis of phenotypic variance. One may regard a so-called common pathway model as a model that contains one or more latent phenotypes that mediate certain genetic and environmental effects on observed variables that function as indicators of those latent phenotypes. As a result the common pathway model enables us to calculate the heritability of both the mediating latent phenotype as well as the observed phenotypes.
One can also interpret a common pathway model as a means to calculate the heritability of certain common variance among a number of observed variables, thus of phenotypic CO-variance, right?
An independent pathway model only contains observed phenotypic variance, no latent phenotypic variance or phenotypic covariance (though it does contain genetic covariance and/or environmental covariance terms that explanation the existence of covariance among the observed phenotypes). My question is if one can still speak of 'heritabilty of the common variance' in an independent pathway model. If so, what is the appropriate way to calculate this heritability? Intuitively I would calculate communalities (sums of the squared standardized loadings) and divide the 'genetic communality' by the sum of the genetic and environmental communality. However, this procedure also sounds like an old-fashioned, rough proxy method.
Any advise on this?