Demystifying a Black Art

I'm working my way through Steve McConnell's Software Estimation: Demystifying the Black Art.

He starts off by making it clear that estimates are NOT the same thing as targets or commitments. Often business partners might ask you for an "estimate" when really what they want is a commitment to a target date.

In fact, estimates should be seen as probability statements. Steve recommends you always give estimates as a range like "2 to 5 weeks", or as a number plus a probability like "I'm about 80% confident I can get this done in 4 weeks." I personally think giving a range is a much better practice - business partners are too quick to forget the stated probability in the latter approach.

So what is a good estimate, for most people not building bridges or nuclear reactors? Here's how he defines a "good estimate:"

A good estimate is an estimate that provides a clear enough view of the project reality to allow the project leadership to make good decisions about how to control the project to hit its targets.

The idea? Get the target date and estimate date range close enough and a good project manager can get the project in on time be shifting resources, simplifying/dropping requirements, etc. The estimate serves as a way to see if you are close enough to make the target date a reality with tweaks along the way.

Anyway, if you are interested in learning more, consider buying the book.