Dear list member,
I deperately need an help in performing a MANOVA in R, but I encountered some problems both in the design and in the synthax with R. I conducted a listening experiment in which 16 participants had to rate the audio stimuli along 5 scales representing an emotion (sad, tender, neutral, happy and aggressive). Each audio stimulus was synthesized in order to represent a particular emotion. Participants had to move 5 sliders each of which corresponded to one of the 5 emotions. The sliders range was [0,10] but participants were only informed about the extremities of the sliders (not at all - very much). There was not a force choice, therefore potentially each audio stimulus could be rated with all the scales (e.g. sad = 0.1, tender = 2.5, neutral = 2., happy = 8.3, aggressive = 1.7). There were 40 stimuli, each stimulus was repeated twice, for a total of 80 trials. I want to demonstrate that the created stimuli were actually correctly classified in the corresponding emotion. For example I expect that happy sounds result in happy ratings by participants and that these happy ratings are greater than the other 4 responses. To analyze the data I want to use a MANOVA with repeated measures. For this purpose I would like to use the audio stimulus as independent variable having 40 levels, while the 5 responses as dependent variables. Since each individual has been measured twice, I include a within-subjects factor for trial number. However, with 40 levels I would have 39 degrees of freedom, that with only 16 participants is not appropriate. For this reason I have also grouped the audio stimuli by their type. So my independent variable could be Trial_type, having 20 levels. Unfortunately, reducing in this way is still too few for 16 participants. Therefore my idea is to perform a MANOVA not on the whole table, but separately for each subset defining an emotion. In this way I would have just 4 lvels. My question is: is this a correct approach to analyze data? Or it is better to use other strategies? For example, looking at the following .csv table which can be downloaded here: https://dl.dropbox.com/u/3288659/Results_data_listening_Test_Grouped.csv I create the subset for emotion Sad, and then I try to perform the MANOVA with repeated measures on it: Sad <- subset(scrd, Emotion == "Sad") model.emotions<-lm(cbind(Sad,Tender,Neutral,Happy,Aggressive) ~ Trial_type,data=scrd) idata<-data.frame(scrd$Trial_number) aov.emotions<-anova(model.emotions,idata=idata, idesign=~ Trial_type, type="III") Unfortunately I get the following error which I am not able to solve: > aov.emotions<-anova(model.emotions,idata=idata, idesign=~Trial, type="III") Error in cbind(M, X) : number of rows of matrices must match (see arg 2) I am not fully sure of the above code, since I am not an expert in R. Can you please correct them showing the correct R code? To the experiment was performed by two groups of listeners: musicians and non-musicians. I created two plots of the results, on for the groups of musicians and the other for the group of non-musicians: https://dl.dropbox.com/u/3288659/exp2_musicians.pdf https://dl.dropbox.com/u/3288659/exp2_non_musicians.pdf Finally, I was not able to find any post hoc test to apply to the result of the MANOVA in case of a significant main effect. Any suggestion? Thanks in advance Best regards Angelo [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
