It is argued that judgments in evaluative research are ultimately subjective, but that good criteria are available to assess their quality. One of these criteria is the robustness of the judgments against incompleteness or uncertainty in the data used to describe the educational system. The use of the robustness criterion is demonstrated through the case of a recent evaluation project in which the state of elementary education in The Netherlands was evaluated. To test robustness, four different procedures were simulated for item removal: (1) scaling; (2) removal of easy items; (3) removal of difficult items; and (4) removal of extreme items. The robustness study demonstrated that the qualifications used in the evaluation project were quite stable under the removal of items from the pool by these four methods. Nearly all the qualifications met the rigorous criterion of robustness. An appendix discusses the independence of the mean observed score of covariation between abilities. (Contains 3 tables, 8 figures, and 17 references.) (Author/SLD)