RE: [R] 2 way repeated measures ANOVA using R: syntax and reportingquestion

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From: F Z (gerifalte28@hotmail.com)
Date: Thu 27 May 2004 - 07:21:58 EST


Message-id: <BAY99-F3SWcfA9piVH000023c89@hotmail.com>

Dear Gideon

Unless you are willing to accept uncorrelated measures in time and
homogeneity of variance I would go for a linear mixed model instead. You
might be surprised on how diffrent can be your results. Try;
>?lme

I hope that this helps

Francisco

>From: GIDEON WASSERBERG <wasserberg@wisc.edu>
>To: "R-help@lists.R-project.org" <R-help@stat.math.ethz.ch>
>Subject: [R] 2 way repeated measures ANOVA using R: syntax and
>reportingquestion
>Date: Wed, 26 May 2004 14:03:21 -0500
>
>Dear Friends
>
>I have a technical question about conducting 2 way repeated measures ANOVA
>analysis using R.
>
>1. Data set: repeated measurement of activity over night (2 hr. intervals)
>repeated (within subject)factor: Hours
>Between subject: Species, Sex
>Dependent variables: specimens
>
>Here is how the data arranged for the analysis:
>
>Subject Replicate Hour Sp. Specimens
>1 1 1 a
>2 1 1 a
>3 1 1 b
>4 1 1 b
>5 2 1 a
>6 2 1 a
>7 2 1 b
>8 2 1 b
>1 1 2 a
>2 1 2 a
>3 1 2 b
>4 1 2 b
>5 2 2 a
>6 2 2 a
>7 2 2 b
>8 2 2 b
>
>
>here's the command I used:
>summary(aov(Specimens~Species*Sex*Hours+Error(Subject/Hours),data=SP)).
>
>My question is - is that the correct way to do it??
>
>2. Below is the results output:
>A. I am not sure I understand what is the meaning of the two error terms I
>get.
>Does the first one show error between subjetcs
>and the second - error within subjects?
>
>Error: Subject
> Df Sum Sq Mean Sq
>Species 1 0.60715 0.60715
>
>Error: Subject:Hours
> Df Sum Sq Mean Sq
>Hours 1 158.24 158.24
>
>Error: Within
> Df Sum Sq Mean Sq F value Pr(>F)
>Species 2 35.19 17.59 34.3017 2.733e-15 ***
>Sex 1 18.98 18.98 37.0092 1.493e-09 ***
>Hours 1 40.02 40.02 78.0278 < 2.2e-16 ***
>Species:Sex 2 1.29 0.64 1.2568 0.2849
>Species:Hours 2 9.95 4.97 9.6993 6.530e-05 ***
>Sex:Hours 1 0.66 0.66 1.2778 0.2585
>Species:Sex:Hours 2 1.38 0.69 1.3498 0.2596
>Residuals 1486 762.20 0.51
>---
>B. How do I summarize this information for a report?
>Is the below suggestion acceptable?
>-------------------------------------------------------------------------------
>
>Source df SS MS F P
>-----------------------------------------------------------------------------
>Species 2 35.19 17.59 34.3 <0.0001
>Sex 1 18.98 18.98 37.01 <0.0001
>Species:Sex 2 1.29 0.64 1.2568 0.2849
>Subject(Species) 1 0.60715 0.60715
>Subject(Hours) 1 158.24 158.24
>Hour 1 40.02 40.02 78.0278 <0.0001
>Species:Hours 2 9.95 4.97 9.6993 <0.0001
>Sex:Hours 1 0.66 0.66 1.2778 0.2585
>Species:Sex:Hours 2 1.38 0.69 1.3498 0.2596
>Residuals 1486 762.20 0.51
>---------------------------------------------------------------------------------
>Very much obliged for your kind response
>
>Gideon
>
>
>Gideon Wasserberg (Ph.D.)
>Wildlife research unit,
>Department of wildlife ecology,
>University of Wisconsin
>218 Russell labs, 1630 Linden dr.,
>Madison, Wisconsin 53706, USA.
>Tel.:608 265 2130, Fax: 608 262 6099
>
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>https://www.stat.math.ethz.ch/mailman/listinfo/r-help
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