Small number statistics

[asterroc]

I am looking for a reliable source to explain to a non-mathematician why drawing conclusions from a sample size of 3 is ridiculous.

Comments

[sirroxton.livejournal.com]

A proper analysis requires an acceptable defect rate, how willing you are to miss a worse defect rate, and how willing you are to get false positives. I can probably dig up an online sample size calculator if you're interested.

But if you want something simple you can convey, if the defect rate was as high as 15%(!), the odds of finding a defect after three checks is a meager:
1 - 0.85*0.85*0.85 = 39%

[sirroxton.livejournal.com]

Of course, if you're trying to identify newly introduced flaws in the manufacturing process itself, checking 3 boxes is perfectly reasonable.