Dear CROSSTALK editor [part 1]

The development of the Earned Schedule (ES) method by Lipke in 2003 has been shown to be an important extension to the Earned Value Management (EVM) method, increasing the utility of EVM data for project schedule analysis, control and oversight. As ES provides a reliable time-based indicator of Schedule Performance, the objective of this paper is to investigate whether the SPI(t) exhibited similar stability characteristics to those extensively reported for the Cost Performance Index (CPI) in EVM. This paper analyzes EVM data from three different countries for projects in three industry segments. Thirty-seven projects were examined for SPI(t) stability and 26 for CPI stability. It has been found that while the behavior of SPI(t) is broadly consistent with CPI, the widely reported CPI stability rule cannot be generalized even within the US Defense Department (US DoD) project portfolio. Further research is required to develop improved understanding of project performance characteristics and the behavior of CPI and the SPI(t).