Schedule Improvement Evaluation

Worksheet 23. Schedule Improvement Evaluation

Activity Ways to Shorten

Time

Time Issue #

Candidate 16 Saved Saved

of Success

16 Expected time saved = estimated time saved X probability of saving this time.

Evaluating Uncertainty Because projects involve the future, their paths are always uncertain. It is common to

find that unanticipated events lead to project delays, cost overruns, quality problems, and even outright failure.

One way to deal with uncertainty and avoid unpleasant outcomes is to conduct what-if analysis to allow the team to anticipate and plan for likely future events. What-if analysis can also help the team improve project performance by manipulating the future to create situations beneficial to project success. For example, a key person might

be persuaded to reschedule a vacation that occurs at a critical time in the project. The task list, project schedule, and analytical charts (Gantt, milestone, and network charts) completed above provide you with tools that can be used to explore various project scenarios and options. For example:

• What if our project had first priority for all of the resources? (This is known as

“crash analysis.”) • What if the work calendar of a key resource were rearranged? • What if a particular resource isn’t available when the project needs it?

In this part of the project plan, the project team will review the project plan’s robustness. That is, team members will evaluate the sensitivity of the plan to changing circumstances. The information obtained will be used to modify the project plan in ways that make it less likely to “break” as the future unfolds in various ways.

Variable Activity, Path, and Project Duration Actually, the team already has some important information on uncertainty: the activity

duration estimates obtained earlier. The optimistic, most likely, and pessimistic estimates differ from one another precisely because the people who provided the estimates were uncertain of the future. This information was used above to calculate weighted averages, which are statistical estimates of the expected duration of a given activity. However, there is addition information embedded in these estimates that will allow us to develop statistical probability distributions for the various paths as well as for the overall project schedule. The worksheet that follows will help you prepare variability estimates for the overall project.

Example of Evaluating Duration Estimates

A simple project consists of only seven tasks, with the estimated durations shown in the table below.

Duration Estimates

Activity Depends

18 (a) 19 (c) 17 Variance Sigma On

A 1 2 3 2.00 0.11 0.33 B A 3 5 9 5.33 1.00 1.00 C B 2 8 14 8.00 4.00 2.00 D C 1 6 13 6.33 4.00 2.00 E B 1 3 7 3.33 1.00 1.00 F E 3 4 8 4.50 0.69 0.83

G D, F 2 6 11 6.17 2.25 1.50

The network chart for this project is shown below. The critical path (using the most likely duration estimates) is indicated as a solid line.

There are several ways in which this information can be analyzed. For example, we could compare the schedules that result from assuming that a given set of durations is correct. The results of this analysis are presented in the table below. This analysis provides best-case, expected, and worst-case scenarios. For the example, the project is scheduled to begin on March 31, 2003. The best-case finish would be April 11, 2003. The two expected finishes are May 7 (based on the weighted averages) or May 6 (using the most likely duration estimates). The worst-case finish would be June 6. These estimates can be compared to the project’s target due date and used for planning. The optimistic analysis can be used in crash schedule planning 20 or the pessimistic analysis can be used for evaluating the effect of shifting resources to higher-priority projects.

17 Weighted average = (a + 4b + c) / 6. 18 Variance = [(c - a) / 6] 2 . 19 Sigma = [(c - a) / 6]. 20 See “Calculating the Cost of a Schedule,” p. 66.

Weighted Average Schedule Most Likely Schedule Task Duration Start

End

Task Duration Start End

A 2d Mon 3/31/03 Tue 4/1/03 B 5.33d

A 2d Mon 3/31/03

B 5d Wed 4/2/03 Tue 4/8/03

C 8d Wed 4/9/03 Fri 4/18/03 D 6.33d