A time-dependent earned value model for software projects

This paper proposes a formal method for including time dependence into Earned Value (EV) management. The model requires three parameters, which map directly to the fundamental “triple constraint” of scope, cost, and schedule: the reject rate of activities, the cost overrun parameter, and the time to repair the rejected activities. Time dependent expressions for the planned value, earned value, and actual cost are derived, along with the cost performance index (CPI) and schedule performance index (SPI). The model is built on the well-established Putnam– Norden–Rayleigh (PNR) labor rate profile, which is a useful representation for large software projects. We apply the model to a well-known software dataset, demonstrating how to estimate the project's final cost, which converges faster to the correct answer with less variability than standard Estimate-at-Completion (EAC) calculations. The model also accurately predicts the required revised labor profile and the new schedule. © 2011 Elsevier Ltd. and IPMA. All rights reserved.