Connor and Herlocker [21] present a different approach in which, instead of
users, they cluster items. Using the Pearson Correlation similarity measure they try
out four different algorithms: average link hierarchical agglomerative [39], robust
clustering algorithm for categorical attributes (ROCK) [40], kMetis, and hMetis 3.
Although clustering did improve efficiency, all of their clustering techniques yielded
worse accuracy and coverage than the non-partitioned baseline. Finally, Li et al.[60]
and Ungar and Foster [72] present a very similar approach for using k-means clus-
tering for solving a probabilistic model interpretation of the recommender problem.