I have tried to use R for the repeated measures experiment design in a phonetic study, and in the resulting forms I met some problems which perturb the final interpretation of the results.
I will explain the experiment design first: the same 7 subjects were answering a question about 25 linguistic stimuli; the stimuli were the same utterances which were processed in 3 different ways (3 conditions), ie each subject listened 25*3 stimuli. I would like to test the effect of condition and of the stimulus on the subjects' performance. My dependent variable is Nboundaries . I think there is: one random effect :subject . 2 within-subject fixed effects: stimulus(25 levels) and condition (3 levels) . Following the explanations of J. Baron, (Notes onthe use of R for psychology...), I have run:
> boundaries.mod<- aov (Nboundaries ~
condition*stimulus +Error(sujet/(condition+stimulus)))
> summary (boundaries.mod)
Error: sujet Df Sum Sq Mean Sq F value Pr(>F) condition 1 0.0044 0.0044 0.0011 0.9743 Residuals 5 19.1133 3.8227
Error: sujet:condition
Df Sum Sq Mean Sq F value Pr(>F)
condition 2 6.3134 3.1567 1.7119 0.22528
stimulus 1 11.5549 11.5549 6.2663 0.02934 * (???)
Residuals 11 20.2838 1.8440
---Error: sujet:stimulus
Df Sum Sq Mean Sq F value Pr(>F)stimulus 24 290.522 12.105 20.3986 <2e-16 *** condition:stimulus 1 0.065 0.065 0.1101 0.7405 (???) Residuals 143 84.860 0.593
---
Error: Within
Df Sum Sq Mean Sq F value
Pr(>F)
condition:stimulus 48 40.984 0.854 1.9854 0.0003245 ***
Residuals 287 123.429 0.430I understand that after removing the effect due to individual subject, the factor condition has no effect (F: 1.7119).
and that the factor stimulus has a strong effect (F:20.3986).
But what are the additional lines (I have inserted the question marks at the end of these lines), which are not present in the examples found in the litterature (Baron, puzzle example) ? They seem to appear when the both involved factors have more than 2 levels. Consequently, I am not sure about the rightness and the interpretation of this model.
I will really appreciate your help.
-- Robert Espesser Laboratoire Parole et Langage UMR 6057, CNRS 29 Av. Robert Schuman 13621 AIX (FRANCE) Tel: +33 (0)4 42 95 36 26 Fax: +33 (0)4 42 59 50 96 http://www.lpl.univ-aix.fr/~espesser mailto:[EMAIL PROTECTED]
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