Stating that intermediate phenotypes are in general no more genetically tractable than other complex traits does, however, ignore the fact that there is variation in genetic architecture. As we have discussed, some phenotypes are more genetically tractable than others, and even a small increase in the mean effect size will improve the chances of gene identification. It is therefore unwise to ignore the opportunities that mapping an intermediate phenotype might provide; the danger lies in assuming that the mapping these traits will be substantially easier than using the psychiatric disease phenotype. In other words, even if one is able to access a suitable intermediate measure, larger effects should not be assumed and moreover, if use of the new phenotype only increases statistical efficiency efficiency and genetic tractability at the cost of meaningfully translated outcomes, their relevance may arguably be limited.
