[R] Getting Sphericity Tests for Within Subject Repeated Measure Anova (using "car" package) (Adjusted Dataset)

[John Fox]

Dear Segios,

For repeated-measures designs, the Anova() function requires a multivariate
linear model fit to the "wide" version of the data set, in which each of the
repeated measures appears as a separate variable. It is necessary that you
have the same occasions observed for all subjects. For your scaled-down
example, you'd have two response variables named, e.g., Sessn1 and Sessn2.
Then you'd fit the multivariate linear model as mod <- lm(cbind(Sessn1,
Sessn2) ~ Trtmnt, data=Dataset). The idata data frame could simply be idata
<- data.frame(Sessn=factor(1:2)). Then you could get the MANOVA and
repeated-measure ANOVA, including sphericity test, etc., as
summary(Anova(mod, idata=idata, idesign=~Sessn)).

I hope this helps,
 John

--------------------------------
John Fox
Senator William McMaster 
  Professor of Social Statistics
Department of Sociology
McMaster University
Hamilton, Ontario, Canada
web: socserv.mcmaster.ca/jfox


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On
> Behalf Of Sergios (Sergey) Charntikov
> Sent: November-09-09 1:18 PM
> To: r-help at r-project.org
> Subject: [R] Getting Sphericity Tests for Within Subject Repeated Measure
> Anova (using "car" package) (Adjusted Dataset)
> 
> [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.
> 
> > Dataset$Sessn <- as.factor(Dataset$Sessn)
> 
> > LinearModel.1 <- lm(Response ~ Sessn*Trtmt, data=Dataset)
> 
> > summary(LinearModel.1)
> 
> All, good so far, but I have problem understanding "idata=" and "idesign="
> functions pertaining to my example.  Session is my repeated measure (Sessn
1
> and Sessn 2 = two sessions, in reality I have more) and it is already
> stacked. Any help or guidance on this matter.
> 
> Thank you, my mock dataset is below.  Each subject has two levels of
> treatment throughout four calendar days which are recoded to Session 1 and
> Session 2 in order to compare treatments by the first and subsequent days
of
> exposure (Treatment x Session; my DV is Response; Session is repeated).
> 
> Subj      Trtmt      Sessn      Response
> 1     N     1     5
> 1     D     1     6
> 1     N     2     4
> 1     D     2     7
> 2     N     1     8
> 2     D     1     9
> 2     N     2     2
> 2     D     2     1
> 3     N     1     4
> 3     D     1     5
> 3     N     2     6
> 3     D     2     2
> 4     N     1     5
> 4     D     1     6
> 4     N     2     4
> 4     D     2     7
> 5     N     1     8
> 5     D     1     9
> 5     N     2     2
> 5     D     2     1
> 6     N     1     4
> 6     D     1     5
> 6     N     2     6
> 6     D     2     2
> 
> 
> 
> Sincerely,
> 
> Sergios Charntikov (Sergey), MA
> 
> Behavioral Neuropharmacology Lab
> Department of Psychology
> University of Nebraska-Lincoln
> Lincoln, NE 68588-0308  USA
> 
> sergioschr-at-gmail-dot-com
> 
> 	[[alternative HTML version deleted]]
> 
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