A fourth explanation to Brooks' Law - The aspect of group developmental psychology

Brooks' Law is often referred to in practice and states that adding manpower to a late software project makes it even later. Brooks' himself gave three explanation only related to concrete task-related issues, like introducing new members to the work being done, communication overheads, or difficulty dividing some programming tasks. Through a description of group developmental psychology we argue for a fourth explanation to the law by suggesting that the group will fall back in its group development when new members are added, resulting in rework setting group norms, group goals, defining roles etc. that will also change over time. We show that this fourth explanation is important when trying to understanding Brooks' Law, and that adding the group developmental perspective might help software development organizations in managing projects.