Incorporating Quality Considerations Into Project Time/Cost Tradeoff Analysis and Decision Making

Existing models and methods of project scheduling implicitly assume uniform quality when evaluating time/cost tradeoffs, but do not model quality explicitly. For a project manager such as a general contractor who subcontracts most tasks of a project, or other project managers who face decisions concerning the level of quality to perform for each task, this is not a realistic assumption. In this paper, we extend the standard discrete time/cost tradeoff problem by assuming that each option for each task is evaluated for its duration, cost, and also its quality. We then provide a mixed integer linear programming model for solving one version of this problem, and illustrate with an example. We next formulate a goal programming mixed integer linear program for a very general version of the problem. This formulation allows for many different definitions of quality, and many combinations of time, cost, and quality goals with preemptive and/or weighted priorities, and is also illustrated with an example. We show how these models can be used to generate quality level curves to illustrate the tradeoffs among time, cost, and quality. These level curves can then be used by project managers to make project scheduling decisions that explicitly model and consider quality as well as time and cost, so that better and more appropriate decisions can be made for a particular situation.