Activity Duration Estimation

Activity Duration Estimating is the determination of the time required to complete the activities that make up the program. This is one of the most difficult aspects of schedule development and should be performed by people who are most familiar with the activity. Two key inputs to the estimation process are the resources required and assigned for the activity and the capabilities of the resources assigned. Historical information (Lessons Learned and Best Practices) from other programs and from commercial databases can also be helpful in developing accurate estimates.

Activity duration estimating is the process for “estimating the number of work periods that will be needed to perform each schedule activity”. Duration can be estimated in units being freely defined by the project. And the durance often is also influenced by the power of the resources and vice versa. Therefore resource estimating und duration estimating as processes should be connected. This includes, that “the duration estimate is progressively elaborated”.

Techniques used for this are

• Expert judgment is used to determine how long an activity might be.
• Analogous estimating is a method for estimating by comparing the actual unit with similar already realized / executed units. Therefore “analogous estimating uses historical information and expert judgment”.
• Parametric estimating computes the durations by formulas which operates on more or less unsure values
• Three-point estimating is a method which estimates not only one value (here: of durance), but the value, which most likely will be reached, and an optimistic value and a pessimistic value. And on the base of these estimated values the method computes variances and probabilities
• Reserve analysis is the process of computing a reserve into the estimated results. These reserved buffers and the method for computing it are explicitly documented and not hidden.

It results in following outputs

• Activity Duration Estimates are estimated durations for each activity given as values (ranges are indicated by +…- add-ons or percent failure values)
• Updates of Activity Attributes are evoked by this process, because the estimated durance of an activity is an attribute of the activity and must be documented.