When calculating the variance of a projects completion time

When calculating the variance of a project\'s completion time, why is it that the \'most likely time\' is not factored into the equation, especially since it carries the most weight in calculating the expected project completion time? I understand that it measures the dispersion of the activity time, but wouldn\'t there be an effect from the \'most likely time\'?

Solution

The variance is square of Standard deviation.

The standard deviation is one sixth of the difference between Optimistic and Pessimistic time. Nearly the entire area lies in +/- 3*standard deviation of the Mean. This is the range of six standard deviation.

In order to compute range, Best and Worst possible time values are required. It has nothing to do with most likely time. The most likely time is crucial to get the accurate estimated time. The Estimated Time and Standard Deviation are used together to find the probability of project completion within the stated time.