Third, we want to test whether all of the genetic risk for AD is shared with the measures of AC. Assuming that model 1a provided the best general fit, this would be performed by fitting model 1d, which eliminates A3—thereby forcing all the genetic risk for AD to derive from the common A1 factor. (If model 1c provided the best fit, it would be possible to test this hypothesis by eliminating A3 from that model [not pictured].)
