1. A method, comprising: identifying a first variable in a source code of a question answering (QA) system; upon determining that a weight applied to a value of the first variable by a first rule in the source code increases a confidence score for candidate answers generated by the QA system beyond a threshold; computing an influence score for the first variable based on: (i) the weight applied to the value of the variable by the first rule in the source code, (ii) a number of rules specifying weights applied to values of the first attribute, (iii) a location of the first attribute in each rule, (iv) a number of times the first variable is used in each rule, (v) a type of operation applied to the value of the first variable by each respective rule, and (vi) an identified phase of a processing pipeline of the QA system in which each respective rule is applied; computing an importance score for the first variable based at least in part on the computed influence score; and upon determining that the importance score exceeds a predefined threshold, storing an indication that the first variable is an important variable relative to other variables specified in the source code; receiving, by the QA system, a case that does not specify a value for the first variable; and refraining, by the QA system, from processing the case.