@conference {liu2010can,
	title = {Can search systems detect users{\textquoteright} task difficulty? Some behavioral signals},
	booktitle = {Proceedings of the 33rd international ACM SIGIR conference on Research and development in information retrieval},
	year = {2010},
	pages = {845{\textendash}846},
	author = {Jingjing Liu and Chang Liu and Gwizdka, Jacek and Belkin, Nicholas J.}
}
