Part II Three: Time Estimates
PERT is useful in handling uncertainty inherent in the project. It handles uncertainty using three time estimates for each activity, namely:
Optimistic Duration -The duration an activity takes in the best case scenario
- Pessimistic Duration – The duration an activity takes in the worst-case scenario
- Normal Duration (MS-Project calls this Expected Duration) – The duration an activity takes in the normal case scenario
- Expected Duration -Duration (MS-Project calls this Duration) – The duration computed by MS-Project using the formula [(optimistic + Pessimistic)+(4 times normal)]/6
This is facilitated by Microsoft Project. It has a special Tool bar titled “PERT Analysis." It allows entry of three time estimates for the entire project or activity by activity.
Microsoft Project also allows optimistic scheduling as well as pessimistic scheduling.
Every one knows that Microsoft Project caters to allocating resources to activities and most people allocate persons to activities. Everyone also knows that resource usage and over-allocation are given by Microsoft Project. However, Microsoft Project does not automatically adjust the schedule if resources are over-allocated. We need to do that using the facility provided by Microsoft Project by choosing Tools > Resource Leveling.
This is very easy to use and Microsoft Project adjusts the schedule within the framework of available resources and minimizes resource over-allocation. If this step is not performed, the resulting schedule may not be accurate reflect the data you have input, in cases of over-allocation of resources.
A resource may not be over-allocated in a single project but may be allocated to other projects and when all allocations are cumulatively taken into consideration, that resource may be over-allocated. Microsoft Project can detect this, if all those projects are scheduled using Microsoft Project.
Duration not Effort
Microsoft Project uses duration in number of business days, not effort. It computes effort by multiplying the duration with the number of hours. So, you need to keep in mind this fact while entering the durations. Set either the start date of the project or the end date. If you set both, then Microsoft Project would treat them as constraints and schedule accordingly and the resulting schedule would not be practical.
Also, do not set dates for interim activities unless they are real constraints. When Microsoft Project reschedules, these constraints would not be changed. Combine resource leveling with this aspect and it would be very difficult to predict the schedule. While Microsoft Project makes the computations perfectly, its not of any practical use at all.
Microsoft Project software is a great tool to add to your project management arsenal. As with any great tool, it is necessary to learn the finer aspects of its inherent backbone and limitations to use it effectively. Microsoft Project places a great deal of functionality into our hands – we need to use it knowledgeably to get reliable and usable results.