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What's Your Fault Feedback Ratio?

By Johanna Rothman
November 4, 2002 12:00 PM ET

Computerworld - Most of us track faults (also called defects, problems, issues, bugs) during the system test part of the project. However, many project managers don't track how many of our fixes are successful and how many fixes are bad -- either introducing a new defect or not completely fixing the original defect. If you're looking for better scheduling of your system test and project completion, start measuring your Fault Feedback Ratio, the FFR.
Here's how to calculate your fault feedback ratio:

Fault Feedback Ratio = Fixes that require more work

All the fixes

When I've measured successful projects, the FFR stays under 10% throughout the project, meaning that no more than one in 10 fixes are problematic as the work progresses. (Don't be deceived by a low FFR and a high overall fault count. With a large total count, the defects can be too overwhelming to successfully manage.) A low FFR and a not-too-high overall defect count also implies that the developers have a relatively easy time finding and fixing the problems. The testers don't have too much trouble keeping up with testing the fixes, because the fixes haven't broken other pieces of the software. The project team is progressing.
On the other hand, an FFR of 15% or higher means that people are spending significant time finding and fixing problems. A higher FFR and a low defect count may mean that the problematic fixes are in the same part of the code base. A higher FFR and normal or high defect counts, may mean the developers may have trouble detecting where to fix the problems, and the testers may have trouble verifying the fixes are good.
Once the FFR hits 20%, you're making dubious progress on the project because your team is spending too much time re-fixing problems they thought were already fixed and retesting those fixes.
Johanna Rothman
Johanna Rothman consults on managing high technology product development, focusing on project management, risk management and people management.
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On one project, the FFR started at 18% in the implementation phase, when the project team started to track their defects. Because the developers had completed the design before they started coding, they had trouble fixing the defects quickly. To make up the time, they took shortcuts for fixing the defects, and stopped doing peer reviews on the new code.
By the time the project was supposed to start system test, the FFR was up to 23%. The project had met its previous milestones, but the team was unable to predict the start of system test. Their previous progress

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