Earned Schedule (ES) is an extension to the theory and practice of
Earned Value Management (
EVM). As of 2005, Earned Schedule is designated as an "emerging practice" by the
Project Management Institute. It was introduced in 2003 a seminal article "Schedule is Different" by Walter Lipke
{Lipke 2003}.
Traditional EVM tracks schedule variances not in units of time, but in units of currency (e.g. dollars) or quantity (e.g. labor hours). Of course, it is more natural to speak of schedule performance in units of time, but the problems with traditional schedule performance metrics are even deeper. Near the end of a project -- when schedule performance is often a primary concern -- the usefulness of traditional schedule metrics is demonstrably poor. In traditional EVM, a schedule variance (SV) of 0 or a schedule performance index (SPI) of 1 indicates that a project is exactly on schedule. However, when a project is completed, its SV is always 0 and SPI is always 1, even if the project was delivered unacceptably late. Similarly, a project can languish near completion (e.g. SPI = 0.95) and never be flagged in a management-by-exception system.
To correct these problems, Earned Schedule theory renames the two traditional measures SV and SPI as SV($) and SPI($), to indicate clearly they are in units of currency or quantity, not time. Then, time-based quantities SV(t) and SPI(t) are created. A stated advantage of Earned Schedule methods is that no new data collection processes are required to implement and test Earned Schedule; it only requires updated formulas. Earned Schedule theory also provides updated formulas for predicting project completion date, using the time-based measures.
It has been stated that Earned Schedule provides a useful link between traditional Earned Value Analysis and traditional project schedule analysis -- a link that some say has been missing in traditional EVM theory.
As of 2006, Earned Schedule tools were becoming available. See Tools below.
Additional Resources:
Earned Schedule Web Site: http://www.earnedschedule.com
Wikipedia: http://en.wikipedia.org/wiki/Earned_Schedule
Tools:
ES Calculator (Excel spreadsheet):
Welcom
