[R] 2.2e-16 a magic number? ks.test help

From: Ashton, Gail <ashtong_at_si.edu>
Date: Fri, 18 Apr 2008 17:53:12 -0400

Hello,
I'm trying to test my data for normality. I enter the data (95ish species counts) run >ks.test (data,pnorm)
and get a p- value <2.2e-16
But this seems to be the p-value no matter what the data I enter. (I have multiple datasets and am testing them all for normality). [Actually, I just entered a vector of 1's and the p-value changed.] When I use the >Shapiro.test command, I get different p-values (different from each other as well as from the ks.test results), and in fact one variable that was significantly different from normal using the ks.test (p<2.2e-16), is not significantly different from normal using the Shapiro.test (p=0.2389).
I am happy to believe that all my data are not normally distributed, but am just suspicious when the p-value remains the same regardless of the data (including log and sqrt transformed data).
Is 2.2e-16 simply the lowest the p-values can go + my data are just really not normal?
Any help much appreciated.
Thanks,
Gail



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