search for: sphericity

I believe that the following function is a good function for eyeballing sphericity. But, I can't find functions for tests anywhere (g-g or h-f). Anyone who wants to can feel free to use it. It is bad that R does not provide any tests for sphericity AND cannot do a MANOVA on repeated measures (although lme is an alternative add on package). One of these solutions must b...

Dear list, first apologies for this is not strictly an R question but a theoretical one. I have read that use of k-means clustering assumes sphericity of data distribution. Can anyone explain me what this means? My statistical background is too poor. Is it another kind of distribution, like gaussian or binomial? What does it happen if the distribution is not spherical? Could you give me an example or a link to information about this? Thanks...

...ivariate approach) using aov() seems straightforward (e.g.: +> myModel<-aov(myDV~myFactor+Error(Subjects/myFactor),data=myData) +> summary(myModel) Where I am currently stuck is how best to deal with the issue of the assumption of homogeneity of treatment differences (in other words, the sphericity assumption) - both how to test it in R and how to compute corrected df for the F-test if the assumption is violated. Back when I taught this course using SPSS it was relatively straightforward - we would look at Mauchly's test of sphericity - if it was significant, then we would use one of the...

I haven't been able to find an answer on this that's direct, only implied. In several places I have read that when people asked for sphericity tests they were guided toward lme or mlm models. But, there is no direct indication that the lme method is not subject to the sphericity assumption. In fact, it seems like it should be. Its just a linear model that handles random and fixed effects. I imagine most other parametric assump...

I'm an experimental psychologist and when I run ANOVA analysis in SPSS, I normally ask for a test of non-sphericity (Box's M-test). I also ask for output of the corrections for non-sphericity, such as Greenhouse-Geisser and Huhn-Feldt. These tests and correction factors are commonly used in the journals for experimental and other psychology reports. I have been switching from SPSS to R for over a year now...

[corrected dataset below] Hello everyone, I am trying to do within subjects repeated measures anova followed by the test of sphericity (sample dataset below). I am able to get either mixed model or linear model anova and TukeyHSD, but have no luck with Repeated-Measures Assuming Sphericity or Separate Sphericity Tests. I am trying to follow example from "car" package, but it seems that I am not getting something right....

Hello Dear R user, I want to conduct a Principal components analysis and I need to run two tests to check whether I can do it or not. I found how to run the KMO test, however i cannot find an R fonction for the Bartlett's test of sphericity. Does somebody know if it exists? Thanks for your help! Thibault [[alternative HTML version deleted]]

Hello everyone, I am trying to do within subjects repeated measures anova followed by the test of sphericity (sample dataset below). I am able to get either mixed model or linear model anova and TukeyHSD, but have no luck with Repeated-Measures Assuming Sphericity or Separate Sphericity Tests. I am trying to follow example from "car" package, but it seems that I am not getting something right....

Hi, Is there a way to do a sphericity test in R for repeated measures ANOVA (using aov or lme)? I can't find anything about it in the help. Thanks Orou [[alternative HTML version deleted]]

Hi R-users Does anybody know if there are functions or packages in R for sphericity tests like Bartlett's or Mauchly's? Thanks! __________________________________________________________ Eng. Agr., M.Sc. Eduardo Dutra de Armas __________________________________________________________ Centro de Energia Nuclear na Agricultura (CENA/USP) Laboratório de Ecotoxicologia Av.Ce...

Dear Prof. Baron, thankyou for your pdf paper on using R, at http://www.psych.upenn.edu/~baron/rpsych.pdf I am currently interested in the sphericity notes on pp. 45-47. The equation on p. 46 suggests the following R calculation: D <- k^2 * ( mean(diag(S)) - mean(S) )^2 while the notes in the pdf indicate the following: D <- k^2 * ( mean(S) - mean(diag(S)) )^2 Can you please consider this and advise the correct calculation? Best, Dar...

...t horses and ungrazed full netting exclosures to exclude all herbivores (A) Site - 6 levels for 6 Sites which are considered fixed Time - 6 levels also for 6 different monitoring or time periods which is where the repeated measures comes in In SPSS there is the option for Bartlett's test of sphericity and Levene's test for whether the variability is homogenous or not. Is it possible to do the same in R with glm? If not, what is the equivalent for testing these assumptions? Also, is it valid to use Tukey's post hocs to test main effects if necessary? If not, is there another method ot...

With respect to calculating the epsilon index of sphericity for ANOVA, discussed on pp. 45-47 of: http://www.psych.upenn.edu/~baron/rpsych.pdf It notes that epsilon is not required for a repeated measures design with only k=2 levels, as the minimum value of epsilon (e) is given by: e = 1/(k-1) so for k=2, we have e = 1 (ie, no correction of the F test...

Hi, I'm getting to grips with using R to perform repeat measures analysis of variance and was wondering is there a potted method to obtain Huynh and Feldt or other adjustments for sphericity violations? Thanks Dominic Dr Dominic J Barraclough Dept Neurobiology and Anatomy, University of Rochester, 601 Elmwood Av, Box 603, Rochester NY 14642 tel (716) 2753627 dominic_barraclough at urmc.rochester.edu -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-h...

Hey, Is this right for a sphericity test? x <- mymatrix mycov <- cov(x) bartlett.text (array (mycov), myconditions)

Does anyone have any suggestions for how to test for violation of the sphericity assumption and apply the Huynh-Feldt correction to a repeated-measure model? My model follows the format below: Rep.anova=aov(Y~X1*X2+Error(Subject/(X1*X2),data=DataFile)) I've already looked at the explanations aov() and Error() in Baron's “Notes on the use of R for psychology ex...

Hello to all, I am trying to use the spherical wavelets package on my altimetry data. I am having some problems now and then. Currently I am having an error of "error in matrix(0,KK,JJ) : too many elements specified" there is a thread of possibly same error (https://stat.ethz.ch/pipermail/r-help/2005-January/064308.html) but it seems like it doesnt really help me. More

.... I don't think I can use power.anova.test() because it does not consider corr=0.40. I am hoping that someone has already implemented the method by Muller & Barton (1989, JASA 84: 549-555) on how to approximate statistical power for a univariate test in repeated-measures ANOVAs when the sphericity assumption is not met. If not, perhaps the MANOVA approach by O'Brien & Kaiser (1985, Psych Bull: 97, 316-33). library(pwr) does not seem to support either. Many thanks in advance, Yuelin Li. ===================================================================== Ple...

...mance time (the dependent measure). The fundamental ANOVA model is: >aov(t.total~group*present.type+Error(subj/present.type), data=dat2) Unfortunately, the standard deviations of the different interaction-cells differ markedly (~20, ~9, ~9, ~18) so it seems that a correction for departure from sphericity is appropriate. I'm trying to achieve that using the Anova function from the car package, but fail to understand what should be the model, the idata and idesign parameter (which seem to be required for a repeated-measures analysis design). I'd appreciate any help with getting the right re...

Hi, If I load 2 packages that have a function with the same name, how do I tell R to run one or the other? (Instead of having R automatically use the first- or last-loaded one, whichever it is. (Which is it, by the way.)) Cheers! Nick -- ==================================================== Nicholas J. Matzke Ph.D. Candidate, Graduate Student Researcher Huelsenbeck Lab Center for