A Discrete, Deterministic Model for Understanding Software Project Development Contingency Profiles

Bruce R. Barkstrom, Paula L. Sidell

This paper describes a simple, discrete deterministic model for the allocation of project contingency as a function of project phase. When a project starts, there is always some uncertainty regarding the resources it will require. As the project proceeds, the participants discover this uncertainty and remove it through the expenditure of resources. In addition, the project may encounter unexpected changes in its environment that force the project to change. The model assumes that the project will eventually discover a (relatively small) number of contingencies, each of which requires the same workforce and duration to resolve. Because the time of appearance and resolution time for each contingency is independent of other contingencies, there may be several overlapping contingencies the project will work on at the same time. Because the model assumes that contingencies suddenly add and subtract staff, managing staff becomes much more complex than is the case with a more uniform staffing plan. In particular, if there are appreciable hiring and firing costs, a project may find it desirable to simply retain staff that can be assigned to contingencies, even though there may be periods with no contingency work.

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