The term program evaluation and review technology (PERT) or English Program evaluation and Review Technique designates a critical path method.

It was developed 1958 in the context of the Polaris project. The special difficulty of the Polaris project consisted of the fact that both research and development and the manufacturing of the components, which were not before ever manufactured at suppliers had to be assigned. Neither costs nor time requirement could become also only approximately accurately estimated. The completion dates could be developed thus only on probability. Each supplier was therefore asked to estimate the time requirement. It is estimated that by PERT the Polaris rocket could be in former times finished two years and thus 45%.

PERT and CPM

PERT resembles strongly the nearly at the same time developed method of the critical path (critical path method), used however instead of the most frequent duration the middle duration of procedures as basis for the computation in the Netzplanung. CPM used for standardizable projects, whose admits procedures from experience of other projects to a large extent are and comparatively little uncertainty exists concerning the time rating. PERT applied with projects with high uncertainty and small experience.

Characteristic of PERT

The time, in which a procedure can be accomplished, does not become estimated with PERT as scalar size. Rather from a probability distribution is proceeded, whereby PERT puts the beta distribution to reason. Usually become for the expenditure estimation of a procedure the minimum or optimistically estimated duration dmin, which needs most frequent (after "“best knowledge"” estimated) duration dnorm, and the maximum or pessimistically estimated duration dmax. From the beta distribution then the middle duration which can be set for the procedure results

d_ {means} = \ frac {d_ {min} + 4 * d_ {standard} + d_ {max}} {6} 

By definition the procedure with a probability is locked of 50% within this time. For possible excesses additionally aimed floats must be taken into account.

With PERT it is possible in addition to indicate also the structure "“not clearly"” (stochastically). The network plan is evaluated by decision knots, whereby there are the following knot types. On the input: AND, OR, EXCLUSIVE ORS; on the original side: deterministically and stochastically).

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