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How to Use Project Evaluation and Review Technique in Critical Path Method

A presentation is made of the essential elements of Project Evaluation and Review Technique as well as of Critical Path Method. Specifically, an overview of how Project Evaluation and Review Technique is used with and impacts Critical Path Method is provided. The overview includes:

• Definition of Project Evaluation and Review Technique
• Definition of Critical Path Method
• How Project Evaluation and Review Technique integration with Critical Path Method Impacts the Results of the Process

As will be illuminated momentarily, project managers tend to turn to Project Evaluation and Review Technique integrated into Critical Path Method when they want to lessen the level of speculation which arises when computing task time frames.

Project Evaluation and Review Technique and Critical Path Method Defined

Program Evaluation and Review Technique is classified as a statistical tool that is utilized in project management. Program Evaluation and Review Technique, or PERT, was developed to represent and analyze the specific tasks involved in the completion of a particular project. PERT was developed in the 1950s by the United States Navy.

Also developed at the same juncture in time was what is know as Critical Path Method, or CPM. CPM is defined as a step-by-step project management system that delineates between critical and non-critical tasks that make up the overall project. The goal of CPM is to prevent interruptions or miscues in a project that would result in time or scheduling issues.

How PERT Impacts CPM

The integration of PERT into CPM results in a slightly more conservative or skeptical view of each of the specific tasks that make up the overall project. At the heart of the manner in which PERT impacts CPM is the fact that CPM alone utilizes one formula and CPM with PERT integration utilizes a different, more stringent one.

Time estimation developed in CPM alone utilizes a three-point analysis:

• The best case estimate
• The most likely estimate
• The worst case scenario estimate

The trio of estimates incorporated into the formula are derived from experienced from other projects. The advice of people skilled in a project area is taken into consideration. In addition, the concept of “best guess” is also brought into play. The formula in CPM standing alone is:

E = (a + 4m + b) / 6

Time estimation developed when CPM is integrated with PERT results in essentially the same based three-point analysis, although it uses slightly different terminology:

• The shortest time
• The likely time
• The longest time

The formula utilized in CPM when PERT is incorporated into the process is:

shortest time + 4 x likely time + longest time
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In the final analysis, the integration of PERT in CPM lessens the reliance on what commonly is referenced as “best guess” in the stand-alone CPM analysis. The hope is that by integrating PERT into CPM, better time calculations are ensured for each individual task that comprise the overall project to be managed. Project scheduling will necessarily always involve some level of speculation; this structure is designed to limit it.

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