The Facts of Change on Software Projects

The Uncertainty Principle in software [ZR97]: Uncertainty is inherent and inevitable in software projects and processes.

The data summarized in Figure 5.1, based on a large study of software projects [Jones97], illustrates that software development is a domain of inventive high-change projects.

Figure 5.1. rates of change on software projects

The X axis plots project size in function points, a language-independent measure of system complexity. The Y axis plots the estimate of overall change or creep in requirements.

function points see www.ifpug.org

Even medium sized projects have change rates around 25%; on very large projects it is 35% or more.

These are high change rates and are at the heart of the motivation for agile and iterative methods.

Further, this data is consistent with another study by Boehm and Papaccio showing that a typical software project experienced a 25% change in requirements [BP88].

This data illustrates that a process, management practice, or value based on the assumption of low change and stability including "reliable" up-front specifications, estimates, and schedules is inconsistent with the nature of software projects.