Mather and Jinks recommend that “So far as possible the non-allelic genes and non-heritable agents should all be additive in action” but also caution that such scales may be hard to find since “Each gene and each non-heritable agent may be acting on its own scale” and the elegance of a parsimonious additive model may be elusive. The problem is that psychiatric geneticists seldom bother to look. We are not blessed with decisions as simple as whether to measure body-weight in kilograms or log-kilograms, though even here the choice of scale will not be neutral with respect to conclusions about the contributions of additive and non-additive effects.
