Software Estimation: Demystifying the Black Art

Chapter 4. Where Does Estimation Error Come From?

There’s no point in being exact about something if you don’t even know what you’re talking about.

—John von Neumann

A University of Washington Computer Science Department project was in serious estimation trouble. The project was months late and $20.5 million over budget. The causes ranged from design problems and miscommunications to last-minute changes and numerous errors. The university argued that the plans for the project weren’t adequate. But this wasn’t an ordinary software project. In fact, it wasn’t a software project at all; it was the creation of the university’s new Computer Science and Engineering Building (Sanchez 1998).

Software estimation presents challenges because estimation itself ...