  This paper gives comprehensive analyses of corpora based on Wikipedia for
several tasks in question answering. Four recent corpora are collected,WikiQA,
SelQA, SQuAD, and InfoQA, and first analyzed intrinsically by contextual
similarities, question types, and answer categories. These corpora are then
analyzed extrinsically by three question answering tasks, answer retrieval,
selection, and triggering. An indexing-based method for the creation of a
silver-standard dataset for answer retrieval using the entire Wikipedia is also
presented. Our analysis shows the uniqueness of these corpora and suggests a
better use of them for statistical question answering learning.
