A method for evaluating the validity of multicomponent measurement instruments in heterogeneous populations is discussed. The procedure can be used for point and interval estimation of criterion validity of linear composites in populations representing mixtures of an unknown number of latent classes. The approach permits also the evaluation of between-class validity differences as well as within-class validity coefficients. The method can similarly be used with known class membership when distinct populations are investigated, their number is known beforehand and membership in them is observed for the studied subjects, as well as in settings where only the number of latent classes is known. The discussed procedure is illustrated with numerical data.