World university rankings use the weight-and-sum approach to process data. Although this seems to pass the common sense test, it has statistical problems. In recent years, seven such problems have been uncovered: spurious precision, weight discrepancies, assumed mutual compensation, indictor redundancy, inter-system discrepancy, negligence of indicator scores and inconsistency between changes in ranking and "Overall". These issues render the validity of ranking results suspect. Moreover, discussion on problems in world university ranking has been conducted mostly at the verbal level with little substantiation of supporting statistics. It is argued that discussion on ranking issues needs statistical evidential support. Modifications to the approach of processing ranking data are suggested.