@article {liu2011understanding,
	title = {Understanding searchers{\textquoteright} perception of task difficulty: Relationships with task type},
	journal = {Proceedings of the American Society for Information Science and Technology},
	volume = {48},
	number = {1},
	year = {2011},
	pages = {1{\textendash}10},
	publisher = {Wiley Subscription Services, Inc., A Wiley Company Hoboken},
	author = {Jingjing Liu and Chang Liu and Yuan, Xiaojun and Belkin, Nicholas J.}
}
