estimates of the main effects. Allowing one locus to affect the average response and the other to affect G × E (da > 0, db = 0, βda = 0, βdb > 0) leads to biased estimates of both genetic parameters. As in other cases fitting the model to untransformed symptom counts (test with equal item parameters) produces substantially biased estimates and misleading conclusions supporting much more complicated models than necessary to account for variation in latent trait values. Consequences include spurious support for epistatic effects on average response and on response to the environment (G × E). If anything, square root transformation only makes matters worse.
