MENTAL MODEL · M6757

PERT

BusinessHigh supportManagement

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Updated 2026-08-08

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INTRODUCTION

English translation pending.

CORE DEFINITION

Program Evaluation and Review Technique (PERT) is a project scheduling method. Each task is estimated three times: optimistic, most likely, and pessimistic. These produce an expected duration and a variance, with the expected duration computed as a weighted average that gives the most likely estimate four times the weight of each extreme. Tasks are arranged in a network diagram, and the critical path is the longest chain of dependent tasks. Summing expected durations and variances along that path yields a distribution for total project duration.

SCAFFOLDING EFFECT

psychology

Reduce cognitive load

- Use three-point estimation: give optimistic, most likely, and pessimistic durations for every task rather than one number. - Use variance summing: add variances along the critical path to get schedule uncertainty, not just a point duration. - Use probability framing: report the chance of finishing by a date rather than promising the date.

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Anchor fast decisions

A single duration estimate hides its own uncertainty, so a schedule built from point estimates looks precise while carrying an unknown chance of being wrong. Collecting three estimates forces the estimator to state a range, and the weighted average moves toward the pessimistic side when that range is wide. Because variances add along a path, uncertainty grows with the number of tasks on it, so long chains are less predictable than their expected duration suggests. The output is a probability.

MINIMUM ACTION

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Practice this model in one real situation:

Break the project into tasks and map their dependencies. 2. Collect optimistic, most likely, and pessimistic durations for each task. 3. Compute an expected duration and a variance for each task. 4. Identify the critical path through the task network. 5. Compute the probability of finishing by the target date.

Check to track your progress (stored locally)

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Source support: Explicit

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en.wikipedia.orghttps://en.wikipedia.org/wiki/Program_evaluation_and_review_techniqueZH · Explicit
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