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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