Figure 4

Power estimated with Raschpower as a function of the standard deviation of the item distribution (\({\sigma _{\delta _{j}}}\)), the group effect (γ) and the gap between the means of the normal distributions (a) for a sample size per groupN _g =200, a number of itemsJ=7 and a variance of the latent variable\({\sigma ^{2}_{\theta }=2}\). Overlaid curves represent different values of a, \(a=\left \{-3/4\sigma _{\delta _{j}},-1/2\sigma _{\delta _{j}}, -1/4\sigma _{\delta _{j}}, 0, 1/4\sigma _{\delta _{j}},1/2\sigma _{\delta _{j}},3/4\sigma _{\delta _{j}}\right \}\).