The recent discussion of PERT took me on a trip into the literature. There was a suggestion that ...
"... there are some quite famous scientists and mathematicians that created these techniques (PERT), but they were also proven by millions of projects executed by hundreds of thousands of project management practitioners."
The first stop is Management of Projects, Peter W. G. Morris, Thomas Telford, London, 1998 who describes in some detail the origins of PERT. That work is then summarized in "Quantitative Risk Analysis for Project Management: A Critical Review," Lionel Galway, RAND Corporation Report WR-112-RC, February 2004, who provides an overview of the "PERT Problem" along with more recent assessment of the artifacts of PERT and their origins.
"The first such quantitative technique of modern project management in the area of schedule risk analysis was the Gantt chart, developed by Henry Gantt in 1917. It provided a graphical summary of the progress of a number of project segments by listing each segment vertically on a sheet of paper, representing the start and duration of each task by a horizontal line along a time scale, and then representing the current time by a vertical line moving from left to right. It is then easy to see where each task should be, and to show its current status.
... computers must be used to set up and maintain the network of tasks; this advance awaited the post-World War II development and widespread deployment of computing power.
The first project to avail itself of these resources was the U.S. Navy’s Polaris program, which began in the mid-1950s to develop nuclear submarines, which could launch nuclear-tipped ICBMs.
The Polaris Special Projects Office (SPO) was under the command of Vice Admiral William F. Raborn, who directed his staff to survey the project management techniques available in American industry to manage technologically complex programs. They found little. Raborn directed a small group of SPO staff and outside contractors to develop a useful control system for the Polaris project, and within a few weeks they developed the Program Evaluation Review Technique or PERT.
PERT was a great success from a public relations point of view, although only a relatively small portion of the Polaris program was ever managed using the technique.
Morris goes on in more detail about the lack of mathematical rigor in the origins of PERT and the reverse engineering (curve fitting) of the parameters to develop the PERT equation - (a+4b+c)/6.
While the PERT equation has served project management in days gone by it has now run its course in the presence of Monte Carlo and the analytical assessment of the errors produced by its use. Along with PERT comes the Critical Path Method, whose deterministic nature was not seen as a draw back for the early users.
The stochastic nature of tasks durations caused the analytical simplicity of PERT and CPM to be replaced by Monte Carlo simulations. The "stochastic CPM" is now a replacement process. Morris again describes how NASA made use of GERT (Graphical PERT) in the mid-60's.
In the end, the problems created by merge bias, stochastic task durations and their inability to be simply (algebraic) summed, the correlation dependencies of tasks and their associated risk adjusted durations, and the multiple critical path and near critical path influences on completion times has made the use of Monte Carlo nearly mandatory for any complex or critical project assessment.
DID 81650 issued this March requires a probablistic risk assessment of the Integrated Master Schedule. This "risk assessment" approach is being replaced with a "program execution" process on most developmental programs in 2005. Monte Carlo has gone mainstream in project management, just as it has gone mainstream in investment analysis and underighting risk analysis.
I promise to put up a bibliography of this topic and the general probabilistic schedule and cost literature in the coming days.