PERT analysis views

PERT analysis is sometimes called what-if analysis, and many project managers use this approach to estimate a probable outcome. The probable outcome that you estimate may be the duration of a task, its start date, or its end date. As a function of the estimating process, you specify the optimistic, pessimistic, and expected durations of tasks in your project. Then Microsoft Project calculates a weighted average of the three durations.

Note PERT stands for Program Evaluation and Review Technique. The Special Projects

Office of the U.S. Navy devised this method of tracking the flow of tasks in the late 1950s.

As you may have guessed, PERT analysis has little to do with the PERT Chart view that was available in Project 98 and earlier versions. But you can use the following PERT analysis views in Project to help you make your estimates:

♦ PA_Optimistic Gantt

♦ PA_Expected Gantt

♦ PA_Pessimistic Gantt

You can use the PERT Analysis toolbar, shown in Figure 6-19, to perform PERT analysis. Choose ViewOToolbarsOPERT Analysis to display the toolbar.

Pessimistic Gantt PERT Entry Form Optimistic Gantt PERT Entry Sheet a

Pessimistic Gantt PERT Entry Form Optimistic Gantt PERT Entry Sheet

Expected Gantt Set PERT Weights Calculate PERT

Figure 6-19: Use this toolbar to help you with PERT analysis tasks.

Tip You need to use the PERT Analysis toolbar to display the four PERT views the first time. After you've displayed the views, you can see them in the More Views ^ window.

PERT Entry Sheet

The PERT Entry Sheet view, shown in Figure 6-20, focuses PERT analysis entirely on durations. Click the PERT Entry Sheet button on the PERT Analysis toolbar to display this sheet.

Using this sheet, you enter optimistic, expected, and pessimistic durations for each task. When you click the Calculate PERT button on the PERT Analysis toolbar, Project uses a weighted average of the numbers that you supply and calculates the probable duration of the task. Project displays the result in the Duration column for that task. Notice the duration of 1.58 days for the Theme task. Project calculated this duration by using the weighted average of the numbers in the Optimistic Dur., Expected Dur., and Pessimistic Dur. columns for the task.

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Figure 6-20: Use this view to focus on entering estimated durations for PERT analysis.

Optimistic Gantt

After you have entered optimistic, expected, and pessimistic durations in the PERT Entry Sheet view and click the Calculate PERT button, you can view the optimistic results for your entire project in the Optimistic Gantt view. Click the Optimistic Gantt button on the PERT Analysis toolbar to display the Optimistic Gantt view. As its name implies, the Optimistic Gantt view, shown in Figure 6-21, is a variation of the Gantt Chart view; the Optimistic Case table is on the left side, and Gantt bars are on the right. You can use this view to enter and evaluate the optimistic scenarios for task durations, start dates, and end dates.

Note Initially, you may not see bars in any of the PERT Gantt views. While displaying any of these views, click the Calculate PERT button on the PERT Analysis toolbar again, and Project displays the bars.

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If you prefer to work with start dates and end dates or to focus entirely on optimistic durations while estimating, you can use this view to enter and evaluate the optimistic scenarios for task durations, start dates, and end dates. If you use this approach, you must also supply the same type of information in the Expected Gantt view and the Pessimistic Gantt view before you click the Calculate button.

Expected Gantt

After you have entered optimistic, expected, and pessimistic durations on the PERT Entry Sheet and click the Calculate button, you can view the expected results for your entire project in the Expected Gantt view. Click the Expected Gantt button on the PERT Analysis toolbar to display the Expected Gantt view, as shown in Figure 6-22. Like its cousins — the Optimistic and Pessimistic Gantt views — the Expected Gantt view is a variation of the Gantt Chart view. Project displays the Expected Gantt table on the left side and Gantt bars on the right side.

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Figure 6-22: Use the Expected Gantt view to help create expected task durations.

If you prefer to estimate with start dates and end dates or to focus entirely on expected durations, you can use this view to enter and evaluate the expected scenarios for task durations, start dates, and end dates. If you use this approach, you also need to supply the same types of information in the Optimistic Gantt view and the Pessimistic Gantt view before you click the Calculate button.

Pessimistic Gantt

After you enter optimistic, expected, and pessimistic durations on the PERT Entry Sheet view and click the Calculate button, you can view the pessimistic results for your entire project in the Pessimistic Gantt view. Click the Pessimistic Gantt button on the PERT Analysis toolbar to display the Pessimistic Gantt view, as shown in Figure 6-23. Like its cousins — the Expected Gantt and the Optimistic Gantt views — the Pessimistic Gantt view is also a variation of the Gantt Chart view. Project displays the Pessimistic Gantt table on the left and Gantt bars on the right. You can use this view to enter and evaluate the pessimistic scenarios for task durations, start dates, and end dates.

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If you prefer to work with start dates and end dates or to focus entirely on pessimistic durations while estimating, you can use this view to enter and evaluate the pessimistic scenarios for task durations, start dates, and end dates. If you use this approach, you also need to supply start and end dates on the Expected Gantt view and the Optimistic Gantt view before you click the Calculate button.

PERT Weights

Project calculates a weighted average when you use PERT analysis. You can control the weights that Project applies to each scenario from the Set PERT Weights dialog box, as shown in Figure 6-24. Click the PERT Weights button on the PERT Analysis toolbar (the second button from the right on the toolbar). Note that the values you enter must sum to 6.

You can use different weights to change the emphasis that Project applies to its calculation of each scenario.

Figure 6-24: Use the Set PERT Weights dialog box to adjust the weights that Project applies when making PERT calculations.

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