Is The Cost of Change Really Low?

Dec 5th, 2002 by Tony in Questioning XP

The original evidence for an exponential cost of change came from Boehm’s book Software Engineering Economics. What most people miss when they read this reference is that there are actually two lines on the famous graph. One supports the well known assertion that various factors combine to “make the error typically 100 times more expensive to correct in the maintenance phase on large projects than in the requirements phase.” There is also a dotted line of the graph that shows data from two smaller, less formal projects. Boehm states, “Although the effect for smaller projects is less pronounced, the 4:1 escalation in costs-to-fix between the requirements phase and the integration and test phase supports the premise.”

Interestingly, even Boehm suggests that sometimes “it may be more cost-effective to proceed with development of a first-cut prototype product rather than spend more effort pinning down requirements in full details … An even stronger case for the prototype approach can be made for small, informal projects with their 4-6:1 cost-to-fix increase, and for problem domains in which rapid prototyping capabilities are available.”

I would contend that modern object-oriented development environments are way more powerful and productive than the prototyping environments that were available back in 1981. Couple this with the Test First Development practices and it would be easy to imagine that a team could do better than a 4:1 cost-to-fix increase.

— Pete McBreen, Questioning Extreme Programming, Chapter 14

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