Environmental index in genetic epidemiology: an investigation of its role, adequacy, and limitations.

The concept of environmental index is briefly reviewed. With a biologically plausible theoretical model, the consequences of indices being based on incomplete information about the familial environment are investigated. It is shown that using partial indices on all family members leads to both an underestimation of the familial environmental component of variance, also called cultural heritability, and, although to a possibly lesser extent, an overestimation of the genetic heritability. It is further shown that so long as complete indices are available on both parents, using identically partial indices on children will yield nearly undistorted parameter estimates. These conclusions were arrived at by using a special case of the model and may not apply in general.