Applied Software Project Management

Chapter 3. Estimation

Many people have referred to estimation as a "black art." This makes some intuitive sense: at first glance, it might seem that estimation is a highly subjective process. One person might take a day to do a task that might only require a few hours of another's time. As a result, when several people are asked to estimate how long it might take to perform a task, they will often give widely differing answers. But when the work is actually performed, it takes a real amount of time; any estimate that did not come close to that actual time is inaccurate.

To someone who has never estimated a project in a structured way, estimation seems little more than attempting to predict the future. This view is reinforced when off-the-cuff estimates are inaccurate and projects come in late. But a good formal estimation process, one that allows the project team to reach a consensus on the estimates, can improve the accuracy of those estimates, making it much more likely that projects will come in on time. A project manager can help the team to create successful estimates for any software project by using sound techniques and understanding what makes estimates more accurate.

Elements of a Successful Estimate

A sound estimate starts with a work breakdown structure (WBS). A WBS is a list of tasks that, if completed, will produce the final product. The way the work is broken down dictates how it will be done. There are many ways to decompose a project into tasks. The project can be broken ...