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The Power of Three (Defect Categories) December 5, 2012

Posted by Tim Rodgers in Project management, Quality.
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Over the last few weeks of software projects at HP we would have cross-functional discussions about open defects to essentially decide whether or not to fix them. We considered the probability or frequency of the defect’s occurrence, and the severity or impact of the defect to the end-user, then assigned the defect to a category that was supposed to ensure that the remaining time on the project was spent addressing the most important outstanding issues.

I don’t remember exactly how many different categories we had in those days (at least five), but for some reason we spent hours struggling with the “correct” classification for each defect. I do recall a lot of hair-splitting over the distinction between “critical,” “very high,” and “high” which seemed very important at the time. Regardless, everyone wanted their favorites in a high-priority category to make it more likely that they would get fixed.

I think we could have saved a lot of time if we had used just three categories: (1) must fix, (2) might fix, and (3) won’t fix. That covers it. Nothing else is necessary. The first group are those defects you must fix before release. The second group are the ones that you’ll address if you have time after you run out of the must-fix defects. The third group are the ones you aren’t going to fix regardless of how much time you have. To be fair, the might-fix defects should be ranked in some order of priority, but at that point you’ve already addressed the must-fix defects and it won’t matter much which defects you choose.

I’m not a psychologist, but I think there’s a big difference between trying to classify things into three categories vs. trying to classify things into more than three categories. I think the human brain gets a little overwhelmed by too many choices. Two might seem better than three because it forces a binary selection, but I think it’s a good idea to compromise and allow for a “maybe” category rather than endure endless indecision.

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