An Introduction to Earned Schedule (ES)

"An Introduction to Earned Schedule (ES)" By Tom Reichner

Earned Schedule as an extension of the Earned Value Management System

Executive Summary

Earned Value Management (EVM) has been widely practiced for nearly 40 years for projects of all sorts. In traditional EVM, a schedule variance (SV) of 0.0 or a schedule performance index (SPI) of 1.0 indicates that a project is exactly on schedule. An SPI of 1.0 or greater is always considered desirable. However, when a project is completed, its SV is always 0.0 and SPI is always 1.0, even if the project was not completed on schedule.

In practice, a project may be nearing completion with an SPI a little less than 1.0 but not be designated as an unacceptable numerical indicator. Practical earned value SV says that this is an exception threshold, and an SPI greater than 0.9 or 0.95 may be considered acceptable.

The United States Department of Energy published a guide for EVM use called “Earned Value Management System” in May 2008.

Earned Schedule (ES) is an extension to the theory and practice of Earned Value Management (EVM). It was introduced in 2003 in an article entitled "Schedule is Different” by Walter Lipke , in The Measurable News, the quarterly magazine of the College of Performance Management, of the Project Management Institute (PMI). It was designated as an "emerging practice" by the Project Management Institute in 2005.

Earned Schedule theory renames the two traditional measurement indicators SV and SPI as SV($) and SPI($), to indicate clearly they are in units of currency or quantity, not time. Time-based quantities in Earned Schedule are labeled SV(t) and SPI(t). One major advantage of the Earned Schedule method is that no new data collection is required. Earned Schedule theory also provides updated formulas for projecting completion date, using the time-based measures.

Proponents of Earned Schedule maintain that it provides a useful link between traditional cost-based EVM and traditional time-based project schedule analysis - a link that some say has been missing in traditional EVM theory.

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