@inproceedings{RecSys-2009-UmyarovT,
	author        = "Akhmed Umyarov and Alexander Tuzhilin",
	booktitle     = "{Proceedings of the Third Conference on Recommender Systems}",
	doi           = "10.1145/1639714.1639722",
	isbn          = "978-1-60558-435-5",
	pages         = "37--44",
	publisher     = "{ACM}",
	title         = "{Improving rating estimation in recommender systems using aggregation- and variance-based hierarchical models}",
	year          = 2009,
}