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25 May 2011

What grows Two Percent Per Month?

In the previous post I introduced using control charts to monitor requirements scope.  Today I want elaborate that further.

Consider the chart above.  There are a nominal 200 requirements, and over time the team are going to deliver on them.

You can see the size of the requirements completed and work remaining from month to month, over a 12 month period. It’s a nice simple diagram that shows a nice even burn down rate. The project team will probably deliver all product scope on time.

Naturally this diagram is based on made up numbers.

The first thing to note is that requirements don’t stay stable. If you have 200 at the beginning of the project once thing you know for certain is that you won’t have 200 by the end.

I have been readings some books by Capers Jones from SPC in the US. One of the facts I gleaned from one of his books is that the IT industry that he works with have a typical 2% per month scope increase.

When I first heard this a few years ago I was fascinated. I wondered what the scope change rate was where I was working and began to start tracking it on the projects I worked on. What I discovered was that in my context the scope change rate was typically much greater than 2%.

Let’s take a look at some scenarios.