20. The method of claim 1 , further comprising calculating a frequency of occurrence of each of the differentiating factors in the plurality of differentiating factors in the evidence passages of the at least two candidate answers, wherein selecting the subset of differentiating factors comprises selecting the subset of differentiating factors based on the frequencies of occurrence associated with each of the differentiating factors.
20. The method of claim 1 , further comprising calculating a frequency of occurrence of each of the differentiating factors in the plurality of differentiating factors in the evidence passages of the at least two candidate answers, wherein selecting the subset of differentiating factors comprises selecting the subset of differentiating factors based on the frequencies of occurrence associated with each of the differentiating factors. 21. The method of claim 20 , wherein selecting the subset of differentiating factors based on the frequencies of occurrence associated with each of the differentiating factors comprises selecting differentiating factors from the plurality of differentiating factors, for inclusion in the subset of differentiating factors, that have associated frequencies of occurrence equal to or above a threshold value.