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From | Nick Cox <njcoxstata@gmail.com> |
To | statalist@hsphsun2.harvard.edu |
Subject | Re: st: sign test output |
Date | Thu, 17 Jan 2013 12:22:37 +0000 |
The row boat [English English: rowing boat] joke is as least as old as a comment in Box. G. E. P. 1953. Non-normality and tests on variances. Biometrika 40: 318-35 which is otherwise germane to the discussion in several ways, not least in introducing the term "robustness". Nick On Thu, Jan 17, 2013 at 12:14 PM, Maarten Buis <maartenlbuis@gmail.com> wrote: > On Thu, Jan 17, 2013 at 11:21 AM, Nahla Betelmal wrote: >> from my readings in statistics , I know that in order to decide >> whether to use parametric or non-parametric tests, the data normality >> distribution should be checked first. >> >> Shapiro-Wilk is used to test normality, when the number of >> observations is less than 30. Otherwise, we should use >> Kolmogorov-Smirnov for large sample (as in my sample). > > Unfortunately that is incorrect. Normality tests need huge samples > before the p-value means what it is supposed to mean. An analogy I > have heard in a different context, but which applies to this situation > very well is: to go out to sea in a row boat to check whether the sea > is safe for the QE II. * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/