Project Estimation

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Project Estimation

Once the project deliverables and activities have been defined, the next step in developing the project schedule and budget is to estimate each activity’s duration. One of the most crucial—and difficult—activities in project management is estimating the time it will take to complete a particular task. Since a resource generally performs a particular task, a cost associated with that particular resource must be allocated as part of the time it takes to complete that task. The time estimated to complete a particular task will have a direct bearing on the project’s budget as well. As T. Capers Jones (Jones 1998) points out:

The seeds of major software disasters are usually sown in the first three months of commencing the software project. Hasty scheduling, irrational commitments, unprofessional estimating techniques, and carelessness of the project management function are the factors that tend to introduce terminal problems. Once a project blindly lurches forward toward an impossible delivery date, the rest of the disaster will occur almost inevitably (120).

In this section, we will review several estimation techniques—guesstimating, Delphi, top-down and bottom-up estimating.
Guesstimating

Estimation by guessing or just picking numbers out of the air is not the best way to derive a project’s schedule and budget. Unfortunately, many inexperienced project managers tend to guesstimate, or guess at the estimates, because it is quick and easy. For example, we might guesstimate that testing will take two weeks. Why two weeks? Why not three weeks? Or ten weeks? Because we are picking numbers out of thin air, the confidence in these estimates will be quite low. You might as well pick numbers out of a hat. The problem is that guessing at the estimates is based on feelings rather than hard evidence.

However, many times a project manager is put on the spot and asked to provide a ballpark figure. Be careful when quoting a time frame or cost off the record, because whatever estimates you come up with often become on the record.

People are often overly optimistic and, therefore, their guesstimates are overly optimistic. Underestimating can result in long hours, reduced quality, and unmet client expectations. If you ever find yourself being pressured to guesstimate, your first impulse should be to stall until you have enough information to make a confident estimate. You may not, however, have that luxury, so the best approach is to provide some kind of confidence interval. For example, if you think something will probably take three months and cost $30,000, provide a confidence interval of three to six months with a cost of $30,000 to $60,000. Then quickly offer to do a little more research to develop a more confident estimate. Notice that even though three months and $30,000 may be the most likely estimate, an estimate of two to six months was not made. Why? Because people tend to be optimists and the most likely case of finishing in three months is probably an optimistic case.


Related Sites/Resources:

Project Estimating Template - Excel File

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