It is useful to compare the heritability results from family-based and SNP-based approaches. Family-based studies, being more direct, typically yield estimates of heritability with lower standard errors, whereas the inaccuracy of estimating distant relationships from genetic data tends to produce fuzzier estimates. Family-based estimates also tend to yield higher estimates of heritability because the familial covariance traces to both rare and common genetic variation, whereas SNP-based estimates mostly arise from covariance due to common genetic variants. Looking at the results summarized above, one might conclude that this is also operating for OCD, i.e., that family-based studies are producing higher heritability estimates than SNP-based studies.
