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Task Information: Defining task distributions

To define statistical distribution for task duration, cost, income, and start time you must define low and base values of duration, cost, income, and start times using appropriate views and dialog boxes. For example, in order to define statistical distribution for cost, you should enter low and high estimates of cost using Cost and Revenue views.

To define distributions.

1. Click the Disbributions tab in the Task Information dialog box.
2. Select the Cost, Income, Duration or Start Time tab.
3. Select the distribution from the Distribution list. If you select Undefined, the base value will be used for all iterations.
4. Define the distribution parameters. The Probability Density chart is automatically updated. You can adjust distribution parameters using the sliders.
5. If you use a custom or discrete distribution, a grid opens. The grid will allow you to define points (or intervals for discrete distributions) and associated with each point (interval)/
6. If you select Normal or Lognormal, you must select the Low and High probability range (P1 and P99, P5 and P95 or P10 and P90). These are "cut-off" parameters; meaning that duration, cost, or start time cannot go beyond these values.

• The Probability Density chart's colors are consistent with those found in the Project Summary and Monte Carlo Simulation Results: Duration is blue, Cost is green, and Start Time is yellow.
• Double-click on the probability density chart to enlarge it.
• To copy the chart to the clipboard or as a JPEG file, right-click and choose a copy command from the shortcut menu.

In most real life examples, the type of distribution (triangular, normal, and lognormal, etc.) may not significantly affect the results of calculation. Results of project scheduling cannot be accurate with high precision due to the large systemic errors of estimation in project management. It is recommended that you assign different statistical distribution if you have reliable historical data about similar tasks.