Graphical Evaluation and Review Technique


Graphical Evaluation and Review Technique, commonly known as GERT, is a network analysis technique used in project management that allows probabilistic treatment both network logic and estimation of activity duration. The technique was first described in 1966 by Dr. Alan B. Pritsker of Purdue University and WW Happ.
Compared to other techniques, GERT is only rarely used in complex systems. Nevertheless, the GERT approach addresses the majority of the limitations associated with PERT/CPM technique. GERT allows loops between tasks. The fundamental drawback associated with the GERT technique is the complex programme required to model the GERT system. Development in GERT includes Q-GERTS - allowing the user to consider queuing within the system.

General GERT rules

GERT uses activity-on-arrow notation only. That means that each activity is described on arrow. The nodes are used to connect activities, but also to determine type and conditions of relations between them.
Each task has two parameters: duration and probability of appearance.
There are three logical operators in GERT which concern activities incoming to the node:
The most common is AND, which means that every incoming activity has to happen before the outcoming one start.
There are also two types of relations that concern activities outcoming from the node:
Its much less popular than PERT or CPM. However it has can offer much more than those methods. PERT or CPM are very popular in most projects, but they have their limitations. The main are:
GERT doesn't have those limitations. But it comes at a cost of more sophisticated diagram.