RT Journal A1 Matthysse S, Holzman P T1 LImitations of the ratio of concordance rates in monozygotic and dizygotic twins-reply JF Archives of General Psychiatry JO Archives of General Psychiatry YR 1989 FD May 1 VO 46 IS 5 SP 479 OP 480 DO 10.1001/archpsyc.1989.01810050093017 UL http://dx.doi.org/10.1001/archpsyc.1989.01810050093017 AB In Reply.—  McGue and Gottesman state that "a true test of the [latent trait] model is obtained only by determining how well it predicts the risk to the monozygotic cotwin of an affected individual or the risk to the offspring of two affected individuals." On the contrary, we believe that the true test of the latent trait model is more pragmatic and even more severe: how effective it will be in discovering linkage between schizophrenia-related phenotypes and chromosomal markers, at least in some pedigrees.The McGue-Gottesman view of modeling sets as a goal constructing a formalism consistent with all the data they choose to amass. This enterprise, however, never leaves this closed world, and in the end, the model is only a shorthand way of expressing the data that have been put into it. This would not be the case if one and only one model could be shown to be