Evaluating Collaborative Filtering Recommender Systems
Herlocker, J. L., Konstan, J. a., Terveen, L. G., & Riedl, J. T.
ACM Transactions on Information Systems (TOIS) '04
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.78.8384&rep=rep1&type=pdf