Precedence diagramming method: Some unusual characteristics and their implications for project managers

Abstract

Abstract The Precedence Diagramming Method, with its activity‐on‐node network and additional precedence relationships, offers an easier and more flexible network approach to modeling large projects than conventional PERT/CPM. But the new relationships (start‐to‐start and finish‐to‐finish constraints) can change some of the basic notions of critical path methodology, including the concept of a critical path itself. Calculations of early and late job start times are affected, along with total slack. Traditional methods of shortening a project by crashing jobs on the critical path can occasionally have anomalous effects. These little‐known characteristics of PDM are discussed, along with their implications for project managers, analysts, and other users of network methodology. Suggestions are made for improving the information available in computer printouts of PDM networks and for avoiding some of the anomalous effects. While PDM improves the project planner's ability to more simply and accurately model large projects, users should be aware of and able to effectively deal with its sometimes peculiar characteristics.