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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jss.2007.03.001 Byline: Stein Grimstad (a)(b), Magne JA[cedilla]rgensen (a) Keywords: Software development; Effort estimation; Expert judgment; Inconsistency Abstract: Expert judgment-based effort estimation of software development work is partly based on non-mechanical and unconscious processes. For this reason, a certain degree of intra-person inconsistency is expected, i.e., the same information presented to the same individual at different occasions sometimes lead to different effort estimates. In this paper, we report from an experiment where seven experienced software professionals estimated the same sixty software development tasks over a period of three months. Six of the sixty tasks were estimated twice. We found a high degree of inconsistency in the software professionals' effort estimates. The mean difference of the effort estimates of the same task by the same estimator was as much as 71%. The correlation between the corresponding estimates was 0.7. Highly inconsistent effort estimates will, on average, be inaccurate and difficult to learn from. It is consequently important to focus estimation process improvement on consistency issues and thereby contribute to reduced budget-overruns, improved time-to-market, and better quality software. Author Affiliation: (a) Simula Research Laboratory, P.O. Box 134, 1325 Lysaker, Norway (b) University of Oslo, Department of Informatics, P.O. Box 1080 Blindern, 0316 Oslo, Norway Article History: Received 17 September 2006; Revised 2 March 2007; Accepted 3 March 2007