t test problem?
Hi Liu, I'd suggest you to use non-parametric tests (see http://www.cas.lancs.ac.uk/glossary_v1.1/nonparam.html) such as: wilcox.test() in stats package pairwise.wilcox.test() in stats package and see the result tou got (significancy/non significancy) and compare it with t test result; Parametric Test Analogous Non-Parametric test Student T-test Wilcoxon Rank Sum Test Paired t-test Wilcoxon Signed Rank Test or the Sign Test to test normality you can use: shapiro.test() in stats package if you decide to use log scale, you must use this for both samples. bye Vito
You wrote:
Hi, Many thanks for your helpful comments and suggestions. The attached are the data in both log10 scale and original scale. It would be very grateful if you could suggest which version of test should be used. By the way, how to check whether the variation is additive (natural scale) or multiplicative (log scale) in R? How to check whether the distribution of the data is normal? PS, Can I confirm that do your suggestions mean that in order to check whether there is a difference between x and y in terms of mean I need check the distribution of x and that of y in both natual and log scales and to see which present normal distribution? and then perform a t test using the data scale which presents normal distribution? If both scales present normal distribution, then the t tests with both scales should give the similar results? Thanks again. Liu ===== Diventare costruttori di soluzioni Visitate il portale http://www.modugno.it/ e in particolare la sezione su Palese http://www.modugno.it/archivio/cat_palese.shtml ___________________________________ http://it.seriea.fantasysports.yahoo.com/