Ten Techniques for Estimating Work (part 2 of 2)

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Estimating is one of the most important parts of project planning. Last week we explored five techniques for estimating effort hours, duration and costs on your project. Here are the remaining five. 

• Work Breakdown Structure. The work breakdown structure allows you to more easily estimate the work. You may look at a large piece of work and have difficulty estimating the effort required. However, as the work is broken into smaller pieces, the individual components will be easier to estimate. When you have estimated all the pieces, add them all together for the overall effort. If you have time to create a good WBS, you usually end up with a good estimate of the overall effort required.
• PERT (Program Evaluation and Review Technique). PERT is an estimating technique that used a weighted average of three numbers to come up with a final estimate. Using the PERT technique, if you are asked to estimate the effort required to complete an activity, you would start with three estimates - the most pessimistic (P) case when everything goes wrong, the most optimistic (O) case when everything goes right, and the most likely (M) case given normal problems and opportunities. The resulting PERT estimate is (O + 4M + P)/6. For example, if the most likely estimate is 10 hours, the optimistic estimate is 6 hours and the pessimistic estimate is 26 hours. The PERT estimate is (6 + 4(10) + 26)/6. The answer is 72/6, or 12 hours. Notice that the number was pulled a little toward the pessimistic estimate, but not by much, since the result is still weighted heavily toward the most likely value.
• Parametric Modeling. In this technique, a pattern must exist in the work that allows you to use an algorithm to drive the overall estimate. For instance, if you know that you can build one mile of flat one-lane highway for one million dollars, you should be able to easily calculate an estimate for ten miles of flat four-lane highway (40 million dollars). 
• Timeboxing. This is a way to set one of the estimates to be within a fixed schedule, budget or scope. Usually when you apply the timebox technique you are forcing the project to be completed by a certain deadline. You then have to focus on the cost and scope aspects of the triple constraint so that the timebox date can be met.
• Function Points (IT development projects). Many industries have specialized estimating models that are customized for their projects. Some IT development organizations use function points as a means to provide meaningful estimates of the work required to complete a systems development project. Function points provide a mechanism to determine the relative complexity of an application. The complexity can be expressed as a count of function points. In this way, an application of 1000 function points is generally ten times larger and more complex than an application of 100 function points.

In the last two weeks we looked at ten different estimating techniques. Every technique will not work in every situation. Knowing the best estimating techniques to apply given the situation will help you provide a more accurate final estimate.