Software Size Uncertainty: The Effects of Growth and Estimation Variability

1,2 Abstract— Examination of currently-accepted software cost, schedule, and defect estimation algorithms reveals a common acknowledgment that estimated software size is the single most influential independent variable. Unfortunately, “The most important business decisions about a software project are made at the time of minimum knowledge and maximum uncertainty.” This includes minimum knowledge and maximum uncertainty about a software product’s effective size at the time when most estimating is done. Further complicating the issue of estimate uncertainty, in the author’s opinion, is the lack of a commonly-accepted taxonomy. This paper proposes definitions for and the relationship between two key contributors to software size uncertainty: growth and estimation process variability, both being distributions, the dispersions of which decrease as a function of project progress.