Hello Dr. McIntosh & others,

Thank you for your response. After reading through the user manual and the comments at the top of the plsanalysis.m script I believe I was able to correctly run a group analysis on my dataset. But I am having trouble understanding the results. 

The command I ran was: 

result=pls_analysis({datamat1_group1,datamat1_group2},[nsubjects1,nsubjects2], 1, opt);

where method = 4 (regular multiblock PLS)

opt.stacked_behavdata = datamat2

Datamat1_group1 is size (33 x 36)

Datamat1_group2 is size (31 x 36)

nsubjects1 = 33

nsubjects2 = 31 

Datamat2 is size (64 x 5), with all participants from group 1 listed first in the same order as they are in datamat1_group1 followed by the participants from group 2 in the same order as they are in Datamat_group2. 

I have run non-group, behavioral PLS before, and I have always had the same number of LVs as columns in datamat2. In the results from my group analysis, I have 12 LVs, even though there are only 5 columns in my dataset2. I assumed that it may be 5 LVs for each group, but I am still not sure what the additional two LVs represent. 

Here is some information on the sizes of the result structures produced by this multiblock pls analysis:  

singular values: size (12 x 1)

lvcorrs: size (10 x 12)

perm_result.sprob: size (12 x 1)

After reading through the documentation, I looked at TBv, which is the task and behavior v values separately. In my case, I believe task refers to groups. TBv contains a 2x12 matrix and a 10x12 matrix. Does this mean that the first two latent variables are task (aka group latent variables? maybe one overall for each?) and the other ten are the 5 for group 1 and the 5 for group 2? I am really not sure how to interpret what each of these latent variables represents in this group analysis. 

It is very possible I am misunderstanding this. I am relatively new to PLS. I have read a few papers and spent a lot of time looking at the matlab code, but conceptually, I am definitely still learning.

Any help in interpreting these results would be greatly apprecaited! 

Best,

Kelly Hiersche 

Hello again,

Thank you for your quick reply. I have used the method=3 on each of my groups, by running separate PLS analysis. I was hoping that by combining my two groups and using method=4 I would be able to test the group differences in my data. Is that correct? 

If so, how do I go about interpretting the results of the 12 LVs?

Thank you for all of your help! 

Kelly 

Thank you very much for the clarification! 

Howdy

For Q1: the order is same as in datamat2.  The errorbars correspond to the "location" of the 95% confidence interval bounds

Q2: this will depend on whether the give LV shows similarities or differences - this you can infer from orig_corr and whether the confidence limits overlap. A lack of overlap suggests a difference, which you can confirm.  if you want to send me a screenshot of some of these resutls I can provide a bit more guidance: rmcintosh@research.baycrest.org

Hi Kelly - thanks for the question.  Behavior PLS when you have more than one group will identify latent variables that captures similarities and differences between groups. Thus, the LV you describe is basically telling you that female and males show the same brain-behavior mapping for the spatial pattern in the and for the behaviors that are reliable by confidence intervals. So, yes very interpretable

An illustration of this is in the appendix of this paper: https://www.dropbox.com/s/7m3mkpdkn54qydm/cipaper.pdf?dl=0

You should think of the first PLS you ran as a sort of omnibus test, which you woud follow up with specific comparisons. What I might suggest next is:

1) run the analysis within group

2) run a few analyses focusing on one or two behaviors to compare the groups directly.

The sensitivity of these will vary a bit, so we may need to do some comparisons back to the omnibus test, which I can tell you how to do if need be (basically you correlate the U matrices between analyses).