The Balance Between Prevention and Inspection
Posted in Development on March 8th, 2010 by Martin Schapendonk – Be the first to commentOne of Deming’s 14 principles states that we should cease dependency on inspection. Does this mean that we should try to eliminate testing in favor of prevention?
Machiel Groeneveld tweeted about (automated) testing, he argued that tests fit Deming’s definition of inspection.
I replied that, when tests are being developed and executed at the same time as the software, you could see that as a form of “build quality in” instead of inspection. That leaves room for interpretation, as Machiel instantly noted. For instance, does that only include developer tests? Or do tests from a separate tester (in the same team) also qualify as built-in quality?
Lars Vonk chipped in that software tests should not be primarily aimed at quality, but as a tool to prevent bugs and as a process improvement tool.
Donald Reinertsen then introduced an economic perspective on the situation. His argument is that there is an economic tradeoff between prevention and inspection. If inspection (and the associated rework) is economically more feasible than prevention, than you may have a legitimate case for inspection, despite Deming’s principle.
Deming’s underlying assumption is that prevention is always cheaper, because to prevent an error from happening again is a one-time investment, while inspection and rework is a recurring cost. An interesting observation is that automated tests may violate this assumption. An automated test lowers test execution cost significantly, maybe even more than the cost of preventing bugs. Reinertsen uses the example of the spelling checker: experience tells us that inspection with a spell checker is cheaper than preventing spelling errors in the first place.
If you or your team are moving more towards prevention instead of inspection, that’s a good thing. But keep in mind that one day, the cost of more prevention might outweigh the cost of inspection and rework. As soon as you hit that point, look for more valuable alternatives to improve your process.
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Anyone? Thnx! 