I'm writing a script that analyses run times of processes. I am not sure of their distribution but I want to know if a process runs "too long". So far I've been using 3 standard deviations of the last run times (n>30), but I was told that this does not provide anything useful if the data is not normal (which it does not appear to be). I found another outlier test that states:
Find the inter quartile range, which is IQR = Q3 - Q1, where Q3 is the third quartile and Q1 is the first quartile. Then find these two numbers:
a) Q1 - 1.5*IQR b) Q3 + 1.5*IQR
The point is an outlier if < a or > b
My data tends to be things like 2sec, 3sec, 2sec, 5sec, 300sec, 4sec, .... where 300sec is obviously an outlier.
Which method is better? The IQR method or the std deviation method?