MATLAB Answers

ranova with two within factors

105 views (last 30 days)
Rose Potter
Rose Potter on 15 Jun 2019
Edited: David on 24 Nov 2020
Hello everyone,
I have a question about how to do a repeated measures anova in Matlab. I have data from 20 people who were tested in 4 conditions each: treatment A pre test, treatment A post test, treatment B pre test, treatment B post test. I want to use time and treatment as factors. However I only managed an anova with one factor. Here's what I got so far:
datatable = cell2table(struct2cell([pre.A, pre.B, post.A, post.B]'));
datatable.Properties.VariableNames = {'pre_A','pre_B','post_A','post_B'};
rm = fitrm(datatable, 'pre_A,pre_B,post_A,post_B~1','WithinDesign',[1:4]);
ranovatable = ranova(rm)
How do I introduce the treatment as a second within factor? I read the documentation but did not find anything I could make use of. Thank you so much in advance!

Accepted Answer

Jeff Miller
Jeff Miller on 16 Jun 2019
Edited: Jeff Miller on 24 Nov 2020
datatable.Properties.VariableNames = {'pre_A','pre_B','post_A','post_B'};
% When you have more than one repeated-measures factor, you must set up a table
% to indicate the levels on each factor for each of your different variables.
% Here is the command you need for this case:
WithinStructure = table([1 1 2 2]',[1 2 1 2]','VariableNames',{'PrePost','TreatAB'});
% The 4 different rows of the WithinStructure table correspond to the 4 different
% columns, 'pre_A','pre_B','post_A','post_B', respectively, in your data table.
% Each 'pre_A','pre_B','post_A','post_B' column is coded as 1/2 on the PrePost factor
% and as 1/2 on the TreatAB factor.
% (Added based on later comments:)
% Indicate that the 1's and 2's of WithinStructure are category labels
% rather than regression-type numerical covariates:
WithinStructure.PrePost = categorical(WithinStructure.PrePost);
WithinStructure.TreatAB = categorical(WithinStructure.TreatAB);
% Now pass the WithinStructure table to fitrm so that it knows how the different
% columns correspond to the different levels of the repeated-measures factors.
rm = fitrm(datatable, 'pre_A,pre_B,post_A,post_B~1','WithinDesign',WithinStructure);
% Finally, you need to specify the repeated-measures factors again when you call ranova, like this:
ranovatable = ranova(rm,'WithinModel','PrePost*TreatAB');
Prabhjot Dhami
Prabhjot Dhami on 24 Nov 2020
I ran into the same issue of extremely small p-values, and what Florian Binder suggested seems to be correct. Make sure the appropriate variables in the WithinStructure are categorical. After doing so with my own data, I compared the Matlab output with SPSS, and they were identical.

Sign in to comment.

More Answers (0)

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!