Manova(rm)
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Manova(rm) & manova1(Responses, GroupVar) can address the same data (if 1 group variable). Yet, they give different statistics. When I run the same data, I get a different probability of rejecting null hypothesis. are there differing null hypotheses? I there a method to tform stats of one to other?
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Adam Danz
le 9 Sep 2019
Modifié(e) : Adam Danz
le 14 Sep 2019
Are you related to Dave Knill? He was on my advisory committee and I admired him deeply as a scientist and an adviser.
The m-file you attached does not define the 'tD' table so I can only run the first 5 lines. Could you add the code used to produce tD?
"Does the "lambda" in Manova1 refer to Wilkes Lambda output in Manova? "
The lambda in Manova1() is a vector of values of Wilk's lambda test statistic for testing whether the means have dimension 0, 1, etc. [1,2]. Manova() also returns the Wilk's lambda statistic [3,4]. I haven't looked into how they are computed and I couldn't run your manova because of the missing table so I can only guess that there may be a different number of degrees of freedom and a different measure of error that results in different lambdas.
The manova() and manova1() functions are flexible with regard to defining the model you're fitting. Here are several examples of repeated measures models [5]. But I hesitate to say wether either of those two functions are restricted to interpreting dependent/independent variables.
If you're providing both models with the same inputs and getting different p-values, it's likely due to the explanation in my answer below but I'd be happy to look at the rm mode if the tD table is provided.
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Adam Danz
le 30 Juil 2019
Modifié(e) : Adam Danz
le 23 Sep 2019
Matlab's documentation is really thin when it comes to many of their statistical methods which makes it difficult to address some of these questions. I guess that's partially why many statistical questions in this forum go unanswered.
The repeated measures MANOVA can be thought of as a within-subjects version of the between subjects MANOVA which is used when groups are independent or unrelated. The repeated measures can be the same test on the same subjects over multiple periods of time or it can be multiple, different tests across the same subjects. Matlab's documentation does provide a decent example of this where 4 different measurements were taken across 3 species of flowers. In your case, if 10 measurements were taken across 2 categories of the same subjects I think a RM design fits your needs. Since the between-subject variability is separated from the within-subjects variability in RM designs, when there is an effect the p-value will be smaller than an ordinary MANOVA. You'll also notice a reduction in the degrees of freedom for RM models.
The manova1() function does not have an input that specifies the 'withinModel' design so it is not set up to perform repeated measures tests.
The manova() method for the RepeatedMeasuresModel class receives inputs from fitrm() which is designed to return a repeated measures model. Within fitrm() you can only specify the within-subject factors, if needed.
One thing to consider with your code is treating BinaryCTNYT as categorical. Fitrm() treats the input variables as continuous unless they are of type categorical, logical, char/string array, or cell array of chars. With your two groupings ([-1,1]) there is no difference in results whether BinaryCTNYT is of class double or categorical but if the groupings were to change (say, [1,2]), the difference between a continuous and categorical interpretation would have a big effect on the results. That variable can be changed to categorical by
tableMD.BinaryCTNYT = categorical(tableMD.BinaryCTNYT);
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Michael Rossen
le 14 Sep 2019
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Adam Danz
le 16 Sep 2019
Hi Mike, I had a chance today to look into these interesting queries and I updated my answer to address some of your questions. Stats questions often get overlooked in this forum but I try to take a stab at them as an excuse to learn something myself. Hopefully it's a bit helpful.
Leonardo Ermini
le 22 Oct 2019
Modifié(e) : Leonardo Ermini
le 22 Oct 2019
Hi all, mine is not an answer but instead a new question, indeed I experienced some problem when delaing with a repeated measures MANOVA. In my case I have 5 dependent variables (thus the MANOVA) measured at two distinct moment in time (thus the repeated mesure model). To explain my case i will recall an example dataset present in matlab:
load repeatedmeas
I do not have any between factors so the Age IQ Group and Gender column are not interesting for me. Anyway: the analogy rely on the fact that we can consider the 8 variables here as 2 set of 4 dependent variables, i.e. 4 dependent variables measured twice, as follows var1 = y1 and y5, var2 = y2 and y6, var3 = y3 and y7, var4 = y4 and y8. The within table semms to express such arrangement. Anyway, let's do the fitrm model:
rm = fitrm(between,'y1-y8 ~ 1','WithinDesign',within)
and run the manova, first without any within factor and the including also the within factors
manova(rm)
manova(rm,'WithinModel','w1*w2')
Then I have compare both the results, in particular the second one, with the SPSS output for a repeated measures MANOVA and the things doesn't match at all!!
Is there somethings I am doing wrong? I cannot not figure if matlab can handle a manova for repeated measure or not, and if not why there is the possibility to set within subjects factors?
Thank yuo in advance,
Leo
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