Schonemann, P. H. and Schonemann, R. D.
Environmental versus genetic models for Osborne's personality data on identical and fraternal twins
Cahiers de Psychologie Cognitive /Current Psychology of Cognition, 1994, 13, 141-167.
It is shown that the additive genetic model of Nichols needed to justify the heritability ratio HR does not fit Osborne's (1980) data very well. A purely environmental model with the same number of parameters fits these data better by a factor of 14.
Compared with the additive genetic model, these empirical results suggest that Osborne's personality data contain no genetic component at all. The responses of the identical twins may be more similar simply because they are exposed to more similar environments than fraternal twins.
This outcome illustrates the general principle that conventional variance component models used to justify heritability estimates are intrinsically inconclusive: We can never rule out that another, qualitatively quite different model may fit the same data equally well or, as in the present case, much better.
A follow-up to Environmental versus genetic variance component models for identical twins, this paper focuses on MZT/DZT data, which naturally are more abundant than the MZT/MZA data used by Jinks and Fulker. But the upshot is similar: Closer inspection of the data reveals that the models needed to justify the heritability estimates do not fit the data. The reasons for this are discussed in non-technical language in Models and muddles.