Damn lies, metrics and statistics

Big Thoughts

28 October 2013 • Written by Peter Bayne

Ignore metrics at your peril, says Peter Bayne. “You can’t fix it if you don’t measure it”

This thought piece was inspired by a tweet from @jeremywaite via @csterwa reminding me of a Dilbert cartoon on the use of metrics by ‘management’.

One constant in my career has been the need to measure. While working in a sawmilling technology research team at Scion in the late ‘90’s, my catch-cry to a very traditional industry became “You can’t fix it if you don’t measure it”. This sentiment is the same in our software industry. If a change is made to software without the means to measure the effect, then all that can be done is to hope that everything is as intended.

If you’re living in the land of the hopeful and don’t know where to start, I suggest looking at something simple, direct and, most importantly, easy to automate. There’s no point in starting out on this endeavour by creating something that is onerous to perform and maintain, as it just won’t last.

For instance, code coverage of unit tests is built in to many systems. Set up a continuous integration system to build the code, run the unit tests on every commit and publish the coverage somewhere visible. Even better, publish the trend over many commits. With this simple metric, you now know which pieces of your code need the most tender loving care.

CoverageTrend

While we are on the topic of unit tests, a unit test itself is a kind of measurement. For instance, when a developer is fixing a bug, how do you measure when the bug is fixed? The simple answer is with a unit test or two. And if (when?) the test is performed in a continuous integration build, the bug’s eradication is ‘measured’ every single time. The same can be said for performance and security tests. Do you run these tests often enough on ALL of the code base so that you can see a trend and be alerted to reductions?

Now, the flip side to adding measurements and metrics is “Why are you measuring that?”.  Metrics, like the code coverage trend, exist for a reason – to invoke change. If you have a couple of hundred metrics calculated every build that are all displayed on a dozen wall-screens and generating multiple emails a day to every developer, the team will get overloaded and simply shut their eyes and ears to the constant noise. There may need to be some focus on the metrics that drive improvement on the current hot topics.

graph all the things

In our example of code coverage, it is usually used most effectively as an alert. Low coverage for an application or module alerts the team that there isn’t much proof of the logic being correct, whereas high coverage doesn’t really prove anything as other quality questions such as dynamic interactions become more interesting.

My final comment is that metrics and trends exist to remind us what we should and shouldn’t be doing – but if they become a target, the metric becomes an end rather than a means to improving quality.

Don’t let the metrics beat you!

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