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Estimation Deflation

The best book I’ve read to date on the topic of software effort and schedule estimation is Steve McConnell‘s “Software Estimation: Demystifying the Black Art“. According to Mr. McConnell, two large influences on the amount of work required to develop a non-trivial piece of software are “size” and “kind“. Regardless of the units of measure (use cases, user stories, function points, Lines Of Code, etc), the greater the “size”, the greater the amount of work required to build the thang. Similarly, the harder “kinds” are associated with lower productivity than the simpler “kinds”.

In his book, McConnell provides the following handy, industry-data-backed,  “kinds” vs “productivity” table that’s parameterized by “size” (in Lines Of Code (LOC)). Note that the “kinds” are sort of arbitrary and by no means an industry standard.

The Real-Time, 10K-100K LOC entry is circled because that’s the type and typical size of software that I specify/design/write. Note the huge 15-to-1 range of productivity for the type. Also note that the table contains large ranges of productivity for all the kind-size entries. Hint, hint: estimating is hard.

Ideally, for psuedo-accurate planning purposes, a software development org maintains its own table (see bogus example below) with real, measured numbers for the sizes of the CSCIs (Computer Software Configuration Items) that its DICs have created.

Of course, for a variety of cultural, competence, and social reasons, a lot of orgs don’t measure or maintain a custom productivity table. Thus, estimators are forced to pull numbers out of their arses and anyone’s productivity estimate is as bad anyone else’s. Everyone who wasn’t born yesterday knows that the pressure to use ridiculously high productivity numbers in work estimates pervades the ether in most orgs. Even when some FAI bucks the trend and withstands the looks and sound bites of disdain for conjuring up a work estimate that is perceived by the management chain as “too high”, the final estimates that show up on “approved” schedules are magically deflated to what is wanted by some clueless BM, SCOL, or CGH.

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  1. October 17, 2010 at 1:05 am

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