On Mon, 11 Jul 2005, S.O. Nyangoma wrote: > Hi there, > If I do an lm, I get p-vlues as > > p-value: < 2.2e-16 > > This is obtained from F =39540 with df1 = 1, df2 = 7025. > > Suppose am interested in exact value such as > > p-value = 1.6e-16 (note = and not <) > > How do I go about it?
You can always extract the `exact' p-value from the "summary.lm" object or you can compute it by hand via pf(39540, df1 = 1, df2 = 7025, lower.tail = FALSE) For all practical purposes, the above means that the p-value is 0. I guess you are on a 32-bit machine, then it also means that the p-value is smaller than the Machine epsilon .Machine$double.eps So if you want to report the p-value somewhere, I think R's output should be more than precise enough. If you want to compute some other values that depend on such a p-value, then it is probably wiser to compute on a log scale, i.e. instead pf(70, df1 = 1, df2 = 7025, lower.tail = FALSE) use pf(70, df1 = 1, df2 = 7025, lower.tail = FALSE, log.p = TRUE) However, don't expect to be able to evaluate it at such extreme values such as 39540. Z ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
