Program Evaluation and Review Technique

The Program Evaluation and Review Technique ( PERT, and event -node representation called ) is an event-oriented network analysis.

History

The technique was developed in 1958 as part of the Polaris project. The particular difficulty of the Polaris project was that both research and development and the manufacturing of the components that have never been made ​​, had to be awarded to suppliers. Neither costs nor time requirement could be even approximately estimated accurately. Completion deadlines could therefore be constructed only on probability. Each supplier was therefore asked to estimate the time required. It is estimated that the Polaris missile could be two years, giving 45% completed earlier by PERT. A related method, the Graphical Evaluation and Review Technique is ( GERT ), with the help of stochastic execution probabilities for individual operations can be mapped.

PERT and CPM

PERT is very similar to the developed almost at the same time the Critical Path Method ( critical path method), but used instead of the most common duration the expected average duration of tasks as the basis for the calculation in the network planning. CPM is used for standardized projects whose operations experience from other projects are widely known and for which there is relatively little uncertainty about the time estimate. PERT is applied in projects with high uncertainty and little experience.

Feature of PERT

The time in which an operation can be performed is not appreciated in PERT as a scalar quantity. Rather, it is assumed that the probability distribution. This sets the PERT beta distribution to reason, which has proven itself for this purpose in practice. In general, for the cost estimation of a process ( so-called three time estimate ), the minimum or optimistic estimated duration dmin, the most common (after " good faith " estimate ) Duration dnorm, and the maximum or pessimistic estimated time needed dmax. For the beta distribution is then obtained the applicable stage of the process mean duration:

In PERT, it is also possible, even the structure of " ambiguous " ( stochastic) indicated. The network is evaluated with the help of decision nodes, where there are the following types of nodes: on the input side of AND, OR, EXCLUSIVE - OR, on the output side of deterministic and stochastic).