This setprovided by Yahoo Japan Corporation and contains 16 million questions asked from April, 2004to April 2009 ting may not necessarily reflect a "real world" distribution of why-questions, in which ideally a wide range of people ask questions that may or may not have an answer in our corpus.
qS3 allows us to evaluate our method under the idealized conditions where we have a perfect answer retrieval module whose answer candidates always contain at least one correct answer (the source passage used for creating the why-question).