When Estimates Go Wrong

George Dinwiddie is an independent software development coach who helps organizations, large and small, to increase the effectiveness of their software development efforts. He provides guidance over a broad range, at the organizational, process, team, interpersonal, and technical levels. He is currently crusading to break down the barriers that hinder effective collaboration between the business, the programmers, and the testers. George is a frequent speaker at Agile conferences. See his blog at http://blog.gdinwiddie.com.

“What’s that ticking sound coming from the engine of the car? Must be a loose valve. I’ll take the car to the mechanic for a valve adjustment…”

At the garage, they look up the flat-rate time estimate for a valve adjustment. It’s easier to estimate when you’ve measured the actual time from lots of competent people doing very similar work. They multiply that time estimate by their labor rates, add in some extra for gaskets, shop supplies and such, and give me a cost estimate. “It should be ready by 5:00.”

I go on my way, knowing I can pick up my car in the evening and how much it’s going to cost me. All is right with the world. But in the late morning, I get a call from the mechanic. “Your car doesn’t need a simple adjustment. The pushrod is bent. The reason it got bent is that the threads holding the rocker arm assembly are stripped out of the cylinder head. We’re going to need to keep your car another day, and the cost will be about triple the original estimate.”

What do I do with this information? I could berate the mechanic for giving me a bad estimate. I could insist that he only charge the originally estimated amount. I could tell him to work through the night so that I can pick up my car first thing in the morning.

I suspect that you don’t do any of those things. I…

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