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Haberman (2008) suggested a method to determine if subtest scores have added value over the total score. The method is based on classical test theory and considers the estimation of the true subscores. Performance of subgroups, for example, those based on gender or ethnicity, on subtests is often of interest. Researchers such as Stricker (1993) and Livingston and Rupp (2004) found that the difference in performance between the subgroups often varies over the different subtests. We suggest a method to examine whether the knowledge of the subgroup membership of the examinees leads to a better estimation of the true subscores. We apply our suggested method to data from two operational testing programmes. The knowledge of the subgroup membership of the examinees does not lead to a better estimation of the true subscore for the data sets.