sharing is not explicitly quantified; and it is difficult to compare between measurements. SEM of twin data addresses all three of these problems. To the authors’ knowledge, only one study has directly compared the results of SEM and means comparison approaches in the selection of candidate endophenotypes.50 This study compared different measurements of “overactivity” and found that the two methodologic approaches yielded similar results because they validated the same measurements as candidate endophenotypes. However, the SEM approach quantified the amount of familial sharing of each measurement with ADHD, allowing future research to explicitly choose those measurements sharing the most familial variance with ADHD. Therefore, twin studies appear to be a valuable strategy for endophenotype research.
