Examining Project Duration Forecasting Reliability

FEATURED PAPER                                                           

Walt Lipke 

Oklahoma City, USA


Earned Schedule (ES) forecasting of project duration has been researched over several years. Overwhelmingly, in comparison to other EVM-based methods, ES has been affirmed to be better. However, the testing results from a study, which employed simulation techniques, indicated there were conditions in which ES performed poorly. These results create skepticism as to the reliability of ES forecasting. This paper examines that study, focusing on the unfavorable results. The analysis put forth indicates ES forecasting to be more reliable than portrayed by the study and is enhanced by the application of the longest path method. 


A research study of project duration forecasting was made several years ago, employing simulation methods applied to created schedules having several variable characteristics (Vanhoucke & Vandevoorde, 2007). Three Earned Value Management (EVM) based methods were compared in the study: 1) EVM [1], Earned Duration (ED) [2], and 3) Earned Schedule (ES) [3]. The overall result from the study was that forecasts using ES, on average, are better than the others. However, in certain instances the ES forecast was not. This result appears counter-intuitive due to the fact that, by its formulation, ES forecasts must converge to the actual final duration. Because of this apparent discrepancy, the conditions of the study are examined for an explanation.

For the study the researchers developed a full range of possible schedule performance scenarios against which the simulations were examined. These scenarios are depicted in figure 1. However, in the research publication, the scenarios were incompletely described. There was insufficient description of several key components of the scenario model. What is meant by the symbols (-, 0, +) in the ovals at the top and left side of the diagram? Likewise, there is lack of definition of the terminology, “Critical activities,” and Non-critical activities.”

It is believed the researchers’ intent of the figure 1 diagram was to show, in a very succinct way, combinations of performance factors (symbols and type of activity) with their associated outcomes, SPI(t) [4] and project duration. However, the lack of clarity in the research paper in describing the meaning of the symbols and activity type has clouded the understanding of the results and conclusions drawn.

Model Description 

The scenario model as shown in figure 1 has nine possibilities. The possibilities are determined from the pairing of the symbols (-, 0, +) between the critical and non-critical activities. For example, “-” for critical activities can be paired with “-,” “0,” and “+” for non-critical activities. Thus, with three pairings for each critical activity symbol, we understand why there are nine scenarios.

What are these symbols? What do they represent? …The symbols are briefly described in the paper to indicate a general condition of schedule performance:


To read entire paper (click here)

About the Author

Walt-Lipkeflag-usaWalt Lipke

Oklahoma, USA 

Walt Lipke retired in 2005 as deputy chief of the Software Division at Tinker Air Force Base. He has over 35 years of experience in the development, maintenance, and management of software for automated testing of avionics. During his tenure, the division achieved several software process improvement milestones, including the coveted SEI/IEEE award for Software Process Achievement. Mr. Lipke has published several articles and presented at conferences, internationally, on the benefits of software process improvement and the application of earned value management and statistical methods to software projects. He is the creator of the technique Earned Schedule, which extracts schedule information from earned value data. Mr. Lipke is a graduate of the USA DoD course for Program Managers. He is a professional engineer with a master’s degree in physics, and is a member of the physics honor society, Sigma Pi Sigma (SPS). Lipke achieved distinguished academic honors with the selection to Phi Kappa Phi (FKF). During 2007 Mr. Lipke received the PMI Metrics Specific Interest Group Scholar Award. Also in 2007, he received the PMI Eric Jenett Award for Project Management Excellence for his leadership role and contribution to project management resulting from his creation of the Earned Schedule method. Mr. Lipke was selected for the 2010 Who’s Who in the World.  At the 2013 EVM Europe Conference, he received an award in recognition of the creation of Earned Schedule and its influence on project management, EVM, and schedule performance research. Most recently, the College of Performance Management announced that Mr. Lipke has been selected to receive the Driessnack Distinguished Service Award, their highest honor. Walt can be contacted at [email protected].

To see previous works by Walt Lipke, visit his author showcase in the PM World Library.