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2004-May-26 21:21 UTC
[R] 2 way repeated measures ANOVA using R: syntax and reportingquestion
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;>?lmeI hope that this helps Francisco>From: GIDEON WASSERBERG <wasserberg at wisc.edu> >To: "R-help at lists.R-project.org" <R-help at 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 > >______________________________________________ >R-help at stat.math.ethz.ch mailing list >https://www.stat.math.ethz.ch/mailman/listinfo/r-help >PLEASE do read the posting guide! >http://www.R-project.org/posting-guide.html_________________________________________________________________