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 <[EMAIL PROTECTED]>
To: "[EMAIL PROTECTED]" <[EMAIL PROTECTED]>
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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