Estimate your tasks more precisely!
Regardless of the technique you use, the tendency in project estimation is to provide one number for each estimate. In many cases you can be more accurate by applying a simple PERT (Program Evaluation and Review Technique) model. PERT is a method of analyzing the tasks involved in completing a given project, especially the time needed to complete each task, and to identify the minimum time needed to complete the total project.
"PERT" was developed primarily to simplify the planning and scheduling of large and complex projects. It was developed for the U.S. Navy Special Projects Office in 1957 to support the U.S. Navy's Polaris nuclear submarine project and it found applications all over industry.
PERT has defined four types of time required to accomplish an activity:
- optimistic time: the minimum possible time required to accomplish an activity (o) or a path (O), assuming everything proceeds
better than is normally expected;
- pessimistic time: the maximum possible time required to accomplish an activity (p) or a path (P), assuming everything goes
wrong (but excluding major catastrophes);
- most likely time: the best estimate of the time required to accomplish an activity (m) or a path (M), assuming everything
proceeds as normal;
- expected time: the best estimate of the time required to accomplish an activity (te) or a path (TE), accounting for the fact
that things don't always proceed as normal (the implication being that the expected time is the average time the task
would require if the task were repeated on a number of occasions over an extended period of time).
_te = (o + 4m + p) ÷ 6_
standard deviation of time: the variability of the time for accomplishing an activity (σte) or a path (σTE)