[R] 2.2e-16 a magic number? ks.test help
ashtong at si.edu
Fri Apr 18 23:53:12 CEST 2008
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.
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