Task leaders provide the raw data for risk analysis. They are chosen for a project because they have knowledge and experience that they can use when doing the necessary task work to complete a project. Their knowledge and experience also gives them a good foundation for speaking with other experienced people about task duration. All of these task leaders do not necessarily have the same experiences, but they each have done very similar things. Carpenters have built frames for other houses, engineers have calculated the air flow through other ducts, programmers have written lines of code for other similar information systems projects, technical writers have written published papers describing similar products, and so on.
After he or she has helped identify the project tasks and has taken owner ship of "my" task(s), the project manager will ask each task leader to report on how long his or her task will take most of the time. Most of the time, represented in this discussion by M, will be the time duration assigned to the task. (It is represented by a bar on the working Gantt chart.) It is absolutely necessary that each task leader supply this most-of-the-time information if a usable Gantt chart is to be created. It is equally important that this information not be padded. It must be an honest estimate of how long the task leader expects the task to take "most of the time."
The project manager must point out to the team members that there is a difference between "most of the time" and "all of the time". It is acknowledged that each task is likely to run over some of the time if the task is repeated over and over. It also is acknowledged by the project manager and the team members that a particular task may overrun its estimated time on "our" project. With dozens to hundreds of tasks, some will overrun their estimated time. The team members do not know in advance which of these tasks will overrun, but they do expect that some will. In addition, they do not wish to be in an embarrassing or threatening situation if one of the tasks that overruns is "mine." Risk Analysis protects team members who execute their task with due diligence from censure if their task overruns.