On Lange and Ryan's plotting technique for diagnosing non-normality of random effects

For linear mixed models, Lange and Ryan's plot [Lange, N., Ryan, L., 1989. Assessing normality in random effects models. Ann. Statist. 17, 624-642] was derived for diagnosing random effect distributions. We show it is sensitive to both non-normality of random effects and mis-specified mean models, and thus may be more useful as a general diagnostic.