I have a hypothesis that a particular intervention/treatment will cause more variation in participant responses to a particular question.
The intervention variable is categorical, with five different treatment groups. The response variable (the participant responses to a question) is a continuous variable.
I don't necessarily expect the means to differ, I just expect greater variation in responses in certain groups as compared to others.
Can anyone advise me on a method to test the difference in the variance of different treatment groups? To be clear, this is not for the purpose of checking the assumption of homogeneity of variance for statistical tests like ANOVA, rather I am interested in specifically if and to what extent the variation differs between the different levels of my categorical intervention/treatment variable.
I thought to run Bartlett's test for homogeneity of variance but (in R at least) I only get an output that shows me whether the variances are homogeneous or not - it doesn't tell me where these differences lie between the different levels of the categorical variable (i.e. is it between group 1 and 5, or group 2 and 3 etc).
I thought also to try to calculate a coefficient of variation for each group and compare these, but I was not sure of a method of how to do this statistically ...
I am probably missing something very obvious, but I cannot find information on how to proceed. Any advice would be much appreciated.