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5.3.5 PERT

Program Evaluation and Review Technique (PERT) is another way of assessing project time. It is very similar to CPA and with the computerisation of project planning techniques PERT and CPA are often used as interchangeable terms.

PERT uses the arrow diagram but differs when it estimates the duration of activities.

PERT requires three estimates for every activity:

  1. t (o) = The most optimistic duration
  2. t (m) = The most likely duration
  3. t (p) = The most pessimistic duration

A formula is then used to calculate the expected time or t (e):

t (o) + 4t (m) + t(p)

t (e) = _________________

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Note that this is really an averaging exercise with a weighting of four times being given to the most likely duration. When there are more than fifty separate activities or tasks to the project, a computer is required to calculate and even update these time estimates.

Some theorists reckon that this PERT formula is too optimistic and prefer a different weighting:

t (o) + 3t (m) + 2t(p)

t (e) = _________________

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In this formula, the pessimistic duration is doubled and the most likely duration reduced to three before the averaging occurs.

Approaches to this form of quantitative or risk analysis has been profoundly advanced with the use of technology. For instance predictive systems, parallel thinking and artificial intelligence systems are being used to speed up and deal with information programmed against multiple variables.

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