Software Project Effort Estimation

Abstract

Plans are nothing; planning is everything. —Dwight D. Eisenhower (quoting 19th-century Prussian General Helmuth von Moltke) One of the reasons for failed estimates is an insufficient background of estimators in the area of software estimation. Arbitrary selection and the blind usage of esti-mation methods and tools often lead to disappointing outcomes, while the under-lying reasons remain unclear. In discussions with corporate management, it is not uncommon to hear the phrase " think of a number and multiply by three. " Deliberate decisions regarding the particular estimation method and its knowledgeable use require insight into the principles of effort estimation. In this chapter, we introduce the basic methodological concepts of software effort estimation. We introduce basic terminology and characterize typical estima-tion stakeholders. Next, we describe the typical context of software effort estima-tion and associated aspects of optimizing software project scope and resources. Further, we summarize typical purposes of effort estimation met in practice, and we sketch a basic estimation process including its primary inputs and outputs. Finally, we overview the project estimation life cycle and illustrate components of project effort estimation. An estimate is the most optimistic prediction that has a non-zero probability of coming true. Accepting this definition leads irrevocably toward a method called what's-the-earliest-date-by-which-you-can't-prove-you-won't-be-finished estimating. What's a better definition for " estimate " ? An estimate is a prediction that is equally likely to be above and below the actual result.