What is the justification for multiplying correlations? I mean, if A correlates with B which correlates with C, that does not necessarily imply that A correlates with C. Simply: correlation is not transitive. Why do you or the authors assume, that the result of such 3 transitional (?) steps will lead to any meaningful results? Besides, what is the purpose of using an estimate for genetic correlation in step 2 if in step 3 the parent-child IQ correlation due to genetic inheritance is used? Step 2 seems unnecessary. Or maybe step 3 should have been IQ and underlying genotype correlation, but then one would need a similar step between parent IQ and parent genotype [step 2.5].