... Data Sparsity, Cold Start Problem, Fraud, Scalability, Gray sheep, Shilling attack and synonymy [6-7, 9, 15] Data Sparsity: In practice, many commercial recommender systems are used to evaluate ... evaluate the performance of the developed systems The evaluation of the systems enables to determine the accuracy of the systems HYBRID RECOMMENDER SYSTEMS A hybrid is combination of at least ... Systems and Computational Intelligence, Harbin, China, 2011 EVALUATION METRICS FOR RECOMMENDER SYSTEMS The performance of recommender system can be evaluated by comparing recommendations to a...