Standard Deviation for Software Development Managers

August 16, 2009 20:43
Bugs that appear during development usually end up in a bugtracking system. Sometimes they even get fixed.
And sometimes, for better findability, each bug gets assigned to a particular area. So instead of having just 60 bugs in a buglog, you get
  • some 20 UI bugs
  • 6 bugs in admin panel
  • 13 bugs in the shopping cart logic
  • 4 integration issues
  • and 17 other uncategorized problems to plod away.

And now you need Math.

Imagine you just put all those amounts onto a chart.



The easiest thing is the mean  - it's just the average for all bug amounts.

  mean = (20+6+13+4+17)/5 = 12

...so the average bug amount is 12. It's the orange line on the plot below - and look, we calculated the differences from it.



Now let's get the variance and the standard deviation:

  variance = (82+(-6)2+12+(-8)2+52) / 5 = 38

  standardDeviation = √variance = √38 = 6.16


The good thing about standard deviation.

The good thing about it is that it's useful. Areas that stand out from it yearn for your attention. Take care of them and keep tabs on the areas that come close to the deviation mark. And everything else will take care of itself.





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