Group Processes in Software Effort Estimation

  • Authors:

  • Kjetil Moløkken-Østvold;Magne Jørgensen

  • Affiliations:

  • Software Engineering Department, Simula Research Laboratory, 1325 Lysaker, Norway kjetilmo@simula.no;Software Engineering Department, Simula Research Laboratory, 1325 Lysaker, Norway magnej@simula.no

  • Venue:
  • Empirical Software Engineering
  • Year:
  • 2004

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Abstract

The effort required to complete software projects is often estimated, completely or partially, using the judgment of experts, whose assessment may be biased. In general, such bias as there is seems to be towards estimates that are overly optimistic. The degree of bias varies from expert to expert, and seems to depend on both conscious and unconscious processes. One possible approach to reduce this bias towards over-optimism is to combine the judgments of several experts. This paper describes an experiment in which experts with different backgrounds combined their estimates in group discussion. First, 20 software professionals were asked to provide individual estimates of the effort required for a software development project. Subsequently, they formed five estimation groups, each consisting of four experts. Each of these groups agreed on a project effort estimate via the pooling of knowledge in discussion. We found that the groups submitted less optimistic estimates than the individuals. Interestingly, the group discussion-based estimates were closer to the effort expended on the actual project than the average of the individual expert estimates were, i.e., the group discussions led to better estimates than a mechanical averaging of the individual estimates. The groups’ ability to identify a greater number of the activities required by the project is among the possible explanations for this reduction of bias.