Chapter 5: Estimate Influences

How much is 68 + 73?

ENGINEER: "It's 141." Short and sweet.

MATHEMATICIAN: "68 + 73 = 73 + 68 by the commutative law of addition." True, but not very helpful.

ACCOUNTANT: "Normally it's 141, but what are you going to use it for?"
—Barry W. Boehm and Richard E. Fairley

Overview

Influences on a software project can be sliced and diced in several ways. Understanding these influences helps improve estimation accuracy and helps improve understanding of software project dynamics overall.

Project size is easily the most significant determinant of effort, cost, and schedule. The kind of software you're developing comes in second, and personnel factors are a close third. The programming language and environment you use are not first-tier influences on the project outcome, but they are a first-tier influence on the estimate. This chapter presents these first-tier influences in decreasing order of significance and concludes with a discussion of second-tier influences.