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I am trying to test some results I have for significance. It has been recommended that I use R and I am completely new to this.

Set-up:

  • Groups: two groups of 8 subjects (16 total)
  • Two conditions: alert and passive
  • Measurements: responses for three different stimuli (A, B, and C) measured in each condition

Experiment: Testing the order of conditions

  • Group one: Alert A, B and C followed by Passive A, B, and C
  • Group two: Passive A, B, and C followed by Alert A, B, and C

Stimuli A, B and C are randomly interleaved in the experiment, does this matter in my ANOVA?

I am interested in making a between and within group comparison of responses to A, B, and C

Here is what I am doing:

My data is arranged in the following way

Group Subject Condition Stimulus  Response
One      S1    Alert          A    _Value_
One      S1    Alert          B    _Value_
One      S1    Alert          C    _Value_
One      S1    Passive        A    _Value_
One      S1    Passive        B    _Value_
One      S1    Passive        C    _Value_
One      S2    Alert          A    _Value_
...

Two      S9    Alert          A     _Value_
Two      S9    Alert          B     _Value_
Two      S9    Alert          C     _Value_
...

This is the code I used:

My_anova = aov(Response ~ Condition * Stimulus * Group + 
           Error(Subject/Condition * Stimulus ), data=My_Data)

Question

  • Is this model correctly specified in R?
share|improve this question
Welcome to the site. I've edited your question to remove the ANCOVA component as it seems quite distinct. I suggest you ask a second question regarding the ANCOVA component and provide a link to the current question in your ANCOVA question. – Jeromy Anglim Oct 7 '11 at 4:26
Thanks for the help Jeromy! – Nick GH Oct 7 '11 at 12:55

1 Answer

up vote 1 down vote

It's very close.

My_anova = aov( Response ~ Condition * Stimulus * Group + 
           Error( Subject/(Condition * Stimulus) ), data = My_Data )
share|improve this answer
Thank you very much! From what I can tell, parenthesis have been added. What does this change in terms of grouping/the ANOVA model? – Nick GH Oct 7 '11 at 12:55
1  
Run both commands and you'll find out. You're not going to break anything trying stuff out. – John Oct 7 '11 at 14:58

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