Before doing normality tests look at fortune(117) and fortune(234). If you still feel the need to have the computer print out a p-value for a test of exact normality, then try SnowsPenultimateNormalityTest in the TeachingDemos package. If you want a test that is more meaningful, then look at vis.test (also in the TeachingDemos package).
-- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare greg.s...@imail.org 801.408.8111 > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r- > project.org] On Behalf Of Ralf B > Sent: Wednesday, June 23, 2010 12:05 PM > To: r-help@r-project.org > Subject: [R] About normality tests... > > Hi all, > > I have two very large samples of data (10000+ data points) and would > like to perform normality tests on it. I know that p < .05 means that > a data set is considered as not normal with any of the two tests. I am > also aware that large samples tend to lead more likely to normal > results (Andy Field, 2005). > > I have a few questions to ensure that I am using them right. > > 1) The Shapiro-Wilk test requires to provide mean and sd. Is is > correct to add here the mean and sd of the data itself (since I am > comparing to a normal distribution with the same parameters) ? > > mySD <- sd(mydata$myfield) > myMean <- mean(mydata$myfield) > shapiro.test(rnorm(100, mean = myMean, sd = mySD)) > > 2) If I just want to test each distribution individually, I assume > that I am doing a one-sample Kolmogorov-Smirnov test. Is that correct? > > 3) If I simply want to know if normality exists or not, what should I > put for the parameter 'alternative' ? Does it actually matter? > > alternative = c("two.sided", "less", "greater") > > Thank you, > Ralf > > ______________________________________________ > R-help@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. ______________________________________________ R-help@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.