The impact of irrelevant information on estimates of software development effort

Software professionals typically estimate software development effort based on a requirement specification. Parts of this specification frequently contain information that is irrelevant to the estimation of the actual effort involved in the development of software. We hypothesize that effort-irrelevant information sometimes has a strong impact on effort estimates. To test this hypothesis, we conducted two controlled experiments with software professionals. In each of the experiments, the software If professionals received specifications describing the same requirements. However, we gave one group of the software professionals a version of the requirement specification where we had included additional, effort-irrelevant, information. In both experiments we observed that the estimates of most likely effort increased when the estimates were based on requirement specifications that contained the information irrelevant to development effort. The results suggest that when estimation-irrelevant information is included as input to expert judgment-based estimation processes, the estimators find it difficult to distinguish between the estimation-relevant and the estimation-irrelevant information. A possible consequence of our findings is that estimation-irrelevant information should be removed from the requirement specification prior to the use of it as input to estimation work.