Chapter 3: Value of Accurate Estimates

[The common definition of 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
—Tom DeMarco

Overview

The inaccuracy of software project estimates—as muddied by unrealistic targets and unachievable commitments—has been a problem for many years. In the 1970s, Fred Brooks pointed out that "more software projects have gone awry for lack of calendar time than all other causes combined" (Brooks 1975). A decade later, Scott Costello observed that "deadline pressure is the single greatest enemy of software engineering" (Costello 1984). In the 1990s, Capers Jones reported that "excessive or irrational schedules are probably the single most destructive influence in all of software" (Jones 1994, 1997).

Tom DeMarco wrote his common definition of an estimate in 1982. Despite the successes I mentioned in the first chapter, not much has changed in the years since he wrote that definition. You might already agree that accurate estimates are valuable. This chapter details the specific benefits of accurate estimates and provides supporting data for them.