Fourth, our models illustrate some of the complexity inherent in comparing the predictive power of an EP and PD. EP have one important starting advantage in which they are typically quantitative, thereby providing more information than the dichotomous diagnostic assessment used for PD. This is especially true for relatively rare PDs like schizophrenia, bipolar illness or anorexia nervosa in which being unaffected is rather uninformative, only indicating that the individual is somewhere in the lower 99% of risk in the population. But the predictive power of EP will be attenuated when it is measured with low reliability, if the genetic risk factors of EP are only partially correlated with those of PD, or if EP is reflecting only a subset of the risk genes.
