1. A computer-implemented method of evaluating candidate answers to questions in a target knowledge domain, the method comprising: identifying, by a question answering module, a plurality of evidence items in the target knowledge domain; identifying, by the question answering module, a plurality of answers to questions in the target knowledge domain; determining, by the question answering module, associations between an evidence item and one or more of the answers including forming an association based at least in part on a value associated with an evidence item supporting or contradicting an answer to a question; and assigning a correlation value for an association between a particular evidence item and a particular answer to a particular question, the correlation value indicating a strength with which the particular item supports or contradicts the particular answer to the particular question: identifying, by the question answering module, an evidence item for which a value has not been received, and identifying, by the question answering module, a most valuable evidence item for which a value has not been received based at least in part on the most valuable evidence item having a highest correlation value of the associations between the plurality of evidence items and the answers to the questions; receiving, by the question answering module from a user, a question receiving, by the question answering module, values for the one or more evidence items; and providing, by the question answering module, an answer to the question in dependence upon the associations between each evidence item and one or more of the answers and the values for the one or more evidence items.