Wednesday, February 20, 2008

Statistical Significance Is Not A License

Please go check out Avinash Kaushik’s blog about statistical significance. I found his blog very helpful and in the entry I like the fact that he begins to discuss how we must use statistics when testing our assumptions. He also points to Brian Teasley’s stats calculator. I pulled this down and tried to find the assumption underneath. I am contacting both, to see if I can get those. I will let you know my thoughts on those.

However, one concern I have, is that it brought up an all too familiar ring to my ear. I am increasingly seeing “Statistical Significance” become a license to do what we want. I want to remind everyone, what statistical significance really means. Simply put, in most cases that we are dealing with, statistical significance indicates that you are x% confident that what you found in your testing or sample, you would find in the general population. In the case of an A/B test, it simply tells you that I am x% confident that there is a difference between A and B and what I found in my testing, I would find in population. That is ALL that it tells you. Furthermore, it is contingent upon you doing the right test the right way in the first place. So, even if you have statistical significance, does not mean what you found was really right. Wrong assumptions, wrong manipulations, and wrong sampling are the issues I find the most often. The sampling piece can be can be the most problematic. You could do a test in one month and find results, and do the same test the next month and find widely different results…both being significant! What went wrong? You probably do not have your assumptions or sampling down pat. Make sure you do that before you test. Otherwise, “statistical significance” can change from the license to do what you want to a pink slip!

Again, I will let you know what I find out about the calculator!


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