Parametric Software Estimation

Commercially available parametric tools can supplement a cost estimator’s techniques. They incorporate models typically built using a broad data set obtained from a variety of software efforts, which may be helpful when developers lack access to data. However, because parametric tools are often closed systems—also called black boxes—the developer cannot easily test the model.

Parametric tools can be used to estimate the cost to develop and maintain software. They are often based on historical data collected from actual projects and typically generate cost, schedule, effort, and risk estimates based on inputs by the user. These inputs may include software size, personnel capabilities, experience, development environment, amount of code reuse, programming language, and labor rates. With these data inputs, the tool draws upon cost estimating relationships and analogies from past projects to calculate the software cost and schedule estimates. When these data are not available to the cost estimator, most tools have default values that can be used instead.

It is important to understand the source of the sizing data used in a regression model. One based on historical data reporting initial estimates at contract award will differ from another that uses historical data reporting final size at contract completion.

Parametric tools may add value in the early stages of the software life cycle, when requirement specifications and design are still vague. For example, these tools provide flexibility by accepting multiple sizing metrics, so that estimators can apply different sizing methods and examine their effects on the estimate.