counting the cost of broken windows

In Quantify the cost of the things you wouldn’t have had to do, if only… Dave Nicolette attempts to calculate the overall cost to his project of a single defect. He arrives at a total of $8,712.50! First, there’s the time spent by the latest developer who got caught by the bug; then there’s the time spent by his two teammates when they helped him debug and fix it; and then there’s the multiplier for all the times this same defect had occurred, but gone unfixed, during the previous two years.

Dave’s figures are compelling, and quite possibly fall on the conservative side – for example, there may have been occasions in the past in which the application hung up during testing, but no-one reported the problem.

I prefer to leave the figure in developer-hours (102.5 in this case), so that we have an indication of the amount of backlog that wasn’t addressed due to this bug: the broken window cost the project almost three developer weeks of progress! If that time had been used to add just one more story, or to release just a little sooner, I wonder what the knock-on costs of this bug would turn out to be, in terms of lost opportunity revenues etc…

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