Hello, Peter Dalgaard wrote: > Not necessarily, but the first suspicion one gets is that what you're > doing with Friedman is not equivalent to what you're doing with ANOVA, > could you show us the code and data (or an outline of it)?
Please find attached the R script and the data input files. The values in dataForFriedmanTest.dat represent the geometric mean of the values of three repetitions for one observer and one condition. Am I doing something wrong there? Thanks in advance Doerte PS: I'm not sure if it is possible to send the dat-files by mail. Therefore I renamed them to *.txt. Please rename back to *.dat. -------- Original-Nachricht -------- > Datum: Fri, 24 Apr 2009 14:52:44 +0200 > Von: Peter Dalgaard <p.dalga...@biostat.ku.dk> > An: Doerte <doerte.ap...@gmx.de> > Betreff: Re: [R] Interpreting the results of Friedman test > Doerte wrote: > > Hello, > > > > I have problems interpreting the results of a Friedman test. It seems > > to me that the p-value resulting from a Friedman test and with it the > > "significance" has to be interpreted in another way than the p-value > > resulting from e.g. ANOVA? > > > > Let me describe the problem with some detail: I'm testing a lot of > > different hypotheses in my observer study and only for some the > > premises for performing an ANOVA are fulfilled (tested with Shapiro > > Wilk and Bartlett). For the others I perform a Friedman test. > > > > To my surprise, the p-value of the Friedman test is < 0.05 for all my > > tested hypotheses. Thus, I tried to "compare" the results with the > > results of an ANOVA by performing both test methods (Friedman, ANOVA) > > to a given set of data. > > While ANOVA results in p = 0.34445 (--> no significant difference > > between the groups), the Friedman test results in p = 1.913e-06 (--> > > significant difference between the groups?). > > > > How can this be? > > > > Or am I doing something wrong? I have three measured values for each > > condition. For ANOVA I use them all, for the Friedman test I > > calculated the geometric mean of the three values, since this test > > does not work with replicated values. Is this a crude mistake? > > Not necessarily, but the first suspicion one gets is that what you're > doing with Friedman is not equivalent to what you're doing with ANOVA, > could you show us the code and data (or an outline of it)? > > -- > O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B > c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K > (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 > ~~~~~~~~~~ - (p.dalga...@biostat.ku.dk) FAX: (+45) 35327907 --
Observer | Condition | Repetition | AUC 2 | 1 | 2 | 11.6698729267 2 | 1 | 3 | 11.3614841831 2 | 1 | 1 | 11.6320875675 3 | 1 | 3 | 11.3813182648 3 | 1 | 2 | 11.9791654383 3 | 1 | 1 | 11.3193295274 4 | 1 | 3 | 11.6271912743 4 | 1 | 1 | 11.7277539642 4 | 1 | 2 | 11.3073525275 6 | 1 | 2 | 11.5356087785 6 | 1 | 3 | 11.8625252416 6 | 1 | 1 | 11.1631417327 7 | 1 | 1 | 12.0811987417 7 | 1 | 2 | 11.4253889199 7 | 1 | 3 | 11.1438163937 8 | 1 | 2 | 12.3351513361 8 | 1 | 1 | 11.0075952969 8 | 1 | 3 | 11.2701354076 1 | 1 | 2 | 11.9582160341 1 | 1 | 3 | 11.3128071894 1 | 1 | 1 | 11.4041971251 2 | 2 | 2 | 11.1937509173 2 | 2 | 1 | 11.6252278612 2 | 2 | 3 | 11.7113976885 3 | 2 | 3 | 11.1192253767 3 | 2 | 1 | 11.3755159053 3 | 2 | 2 | 12.0029900345 4 | 2 | 3 | 11.6105418939 4 | 2 | 2 | 11.4205387926 4 | 2 | 1 | 11.5200504433 6 | 2 | 2 | 11.3150843227 6 | 2 | 3 | 11.087942451 6 | 2 | 1 | 12.0640315424 7 | 2 | 1 | 11.6605537521 7 | 2 | 3 | 11.6189671844 7 | 2 | 2 | 11.2636316548 8 | 2 | 3 | 11.3865060588 8 | 2 | 2 | 12.1672455368 8 | 2 | 1 | 10.9692943665 1 | 2 | 3 | 11.4617141335 1 | 2 | 1 | 11.5455368466 1 | 2 | 2 | 11.5463396473 2 | 3 | 2 | 11.3473263733 2 | 3 | 1 | 11.7839556008 2 | 3 | 3 | 11.1316960504 3 | 3 | 3 | 11.8686526315 3 | 3 | 2 | 11.0739149317 3 | 3 | 1 | 11.403959013 4 | 3 | 1 | 11.5870552325 4 | 3 | 2 | 11.3401354648 4 | 3 | 3 | 11.3424292954 6 | 3 | 3 | 11.3615420894 6 | 3 | 1 | 11.4887245966 6 | 3 | 2 | 11.3741010608 7 | 3 | 2 | 11.3180993919 7 | 3 | 1 | 11.4960941843 7 | 3 | 3 | 11.454173957 8 | 3 | 3 | 11.2121329748 8 | 3 | 1 | 11.5712149501 8 | 3 | 2 | 11.4525667984 1 | 3 | 3 | 11.1470495671 1 | 3 | 1 | 11.3843720685 1 | 3 | 2 | 11.7803942389 2 | 4 | 1 | 11.7049906947 2 | 4 | 2 | 11.3104231298 2 | 4 | 3 | 11.6789580111 3 | 4 | 2 | 11.9600062087 3 | 4 | 3 | 11.2497720322 3 | 4 | 1 | 11.5070118114 4 | 4 | 3 | 11.6880141384 4 | 4 | 2 | 11.6823046979 4 | 4 | 1 | 11.3789895286 6 | 4 | 1 | 11.2340767853 6 | 4 | 3 | 12.0463303433 6 | 4 | 2 | 11.4281136904 7 | 4 | 2 | 11.9397313286 7 | 4 | 1 | 11.5816813225 7 | 4 | 3 | 11.2157780218 8 | 4 | 3 | 11.3649382115 8 | 4 | 1 | 11.7537482956 8 | 4 | 2 | 11.6151737679 1 | 4 | 2 | 11.8833021895 1 | 4 | 1 | 11.6774568059 1 | 4 | 3 | 11.218661679
1 | 11.5549259143 | 11.5177949943 | 11.4343007933 | 11.5897878773 2 | 11.5536609678 | 11.5078788328 | 11.4177885112 | 11.5633767055 3 | 11.5561528638 | 11.4933075157 | 11.4442169793 | 11.5685580088 4 | 11.5527009607 | 11.516782224 | 11.4226218647 | 11.5821980029 5 | 11.5527009607 | 11.516782224 | 11.4226218647 | 11.5821980029 6 | 11.516876305 | 11.4815469835 | 11.4079793857 | 11.564376866 7 | 11.5435216828 | 11.5129966958 | 11.4225358663 | 11.5752893725 8 | 11.5236136682 | 11.4970692787 | 11.4109905276 | 11.5768318539
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