15. An apparatus comprising: a processor; and a memory coupled to the processor, wherein the memory comprises instructions which, when executed by the processor, cause the processor to: receive an input question for which an answer is sought; extract features of the input question based on a natural language processing of the input question; execute a first search of a corpus of documents based on a first subset of the extracted features of the input question and an initial evaluation of a utility of the first subset of extracted features to generate a subset of documents matching the first subset of extracted features, wherein the utility of the first subset of extracted features identifies a degree to which each feature of the first subset of extracted features of the input question discriminates between documents in the corpus of documents that are sources of candidate answers to the input question; execute a second search of a set of passages extracted from the subset of documents based on a second subset of the extracted features of the input question and a reevaluation of the utility of the second subset of extracted features forming a subset of passages, wherein the utility of the second subset of extracted features identifies a degree to which each feature of the second subset of extracted features of the input question discriminates between passages in the set of passages that are sources of candidate answers to the input question; and generate query results from the subset of passages from which a set of candidate answers for the input question are identified.
18. The apparatus of claim 15 , wherein the instructions to execute the second search of the set of passages extracted from the subset of documents based on the second subset of the extracted features of the input question and the reevaluation of the utility of the second subset of extracted features further cause the processor to: generate a second statistical data structure for the set of passages; and identify the query results from the subset of passages comprised within the second statistical data structure relevant to the second subset of the extracted features utilizing the reevaluation of the utility of the second subset of extracted features.