A Measure of Clustering in Free Recall Utilizing the Parameters of the Original Stimulus List

A measure of clustering in free recall based upon the parameters of the original stimulus list (R/Opt. R) was proposed and compared with five other measures for eight recall protocols. The R/Opt. R measure was shown to be relatively independent of the length of the recall protocol, but yielded higher scores where fewer categories were utilized. Optimum clustering was defined not simply in terms of perfect ordering of elements within the protocol but also in terms of the number of categories and items within those categories in the original stimulus list.