Rion Snow Brendan O'Connor Daniel Jurafsky Andrew Y. Ng Cheap and Fast - But is it Good? Evaluating Non-Expert Annotations for Natural Language Tasks. 254-263 2008 EMNLP http://www.aclweb.org/anthology/D08-1027 conf/emnlp/2008 db/conf/emnlp/emnlp2008.html#SnowOJN08