Clustering, dependence and ratio scales in AHP: Rank reversals and incorrect priorities with a single criterion

In the analytic hierarchy process, it is often thought that rank reversals cannot occur in a single-criterion problem. This paper demonstrates that if it is necessary to cluster items under a single criterion, such reversals are possible. The reversals occur prior to aggregating across clusters and are caused by a failure to make reference to the alternatives when performing criteria comparisons. Rank reversals, however, are only a symptom of the problem. The real problem is a failure to calibrate global weights to a common scale which spans different clusters. Even in the absence of reversals, aggregated weights from the AHP’s relative mode of measurement can fail to maintain composite ratio relationships.