Normal distribution test
On 11/17/2009 10:07 AM, rkevinburton at charter.net wrote:
This is probably an even more basic question but shapiro.test return both the statistic (w) and the significance (pw) of the statistic. For this test the null-hypothesis is that the distirbution is not normal so very small values of pw would mean that there is very little chance that the distiribution is not normal. Correct?
I think you have an extra "not" in your description of the null. But more importantly, a small p-value just means that you had a value of the test statistic that would be unusually extreme if the null was true. Whether that means there is a small probability of the null being true depends on information outside the test. It's essentially a Bayesian question, and Bayesians wouldn't base their decision on just the p-value. For example, if I flip a fair coin 100 times and see 30 heads, binom.test() tells me that the p value would be 7.85e-05. That doesn't mean the probability that the coin is fair is low: it just means I saw an unusually small number of heads. Now if I wasn't sure whether the coin was fair or not, I'd take the low p-value as evidence that it was not. But the p-value alone isn't sufficient to let me calculate a probability of the null being true. Duncan Murdoch
Thank you. Kevin ---- Johannes Graumann <johannes_graumann at web.de> wrote:
Markus Mehrwald wrote:
Hi all, I am completely new to R and my knowledge of statistics is quite small so I hope you can help my. I have three dimensional point data which represents (and this is what I do not know for sure) a normal distribution. Now I want to test if this is true or not and as I can remember from statistics lessons I can use Chi-Square test for distribution test. BUT: I have realy no idea how to do this with R and additionally if my assumptions are correct and if this is possible with R at all. Thank you very much in advance for any answer. Markus
See ?shapiro.test or ?ks.test HTH, Joh
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______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.