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Why Critical Path Scheduling (CPM) is Wildly Optimistic

A pessimist sees the difficulty in every opportunity;
an optimist sees the opportunity in every difficulty.

Winston Churchill

Keywords: Scheduling, Complexity, Communications

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Why Critical Path Scheduling (CPM) is Wildly Optimistic  [P117]

The ‘critical path’ methodology developed in an environment of certainty.  This paper will suggest that when dealing with major projects in the modern age, the projected end date calculated by CPM tends to be widely optimistic. However, through the prism of complexity, in particular CRPR, and/or motivational theory this is not necessarily a bad thing.

The factors that drive CPM towards an optimistic initial assessment include psychological biases, single point estimates and limitations of the CPM modelling process (including a factor previously identified as PERT Merge Bias).  As work progresses, these initial biases are compounded by the inability of CPM to adjust future predictions based on performance to date. Some of the solutions developed from EV theory such as ‘Earned Schedule’ provide a partial answer but are also limited.

From the perspective of CRPR and motivation theory, having an optimistic schedule can be beneficial. Concepts such as Critical Chain are based on the value of an optimistic schedule as a motivator and behavioural change agent. Therefore, if used as a motivational communication tool, the ‘optimistic schedule’ has many advantages.

The challenge is fitting an optimistic scheduling process within the constraints of an organisational governance structure that requires an accurate prediction of the likely completion date and traditional contracts that demand a ‘contract schedule’ and include significant sanctions if the CPM schedule predictions prove incorrect.

The paper will review a number of emerging methodologies including Critical Chain, Momentology, RD-CPM® and Schedule Density. It will conclude by suggesting a range of practical measures based on embracing uncertainty and using predictive tools that in combination can provide the degree of insight, motivation and control needed to blend the desirability of an optimistic schedule as a workforce motivator with management’s need for a predictable and reliable project completion date.
 

Author: Patrick Weaver

Presented at:


Eighth Annual PMI College of Scheduling Conference
Sunday, May 1 - Wednesday, May 4, 2011

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