help > Repeated measures (2) t-test validation
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Feb 27, 2024  11:02 AM | dylan sutterlin - university of montreal
Repeated measures (2) t-test validation

Hi,


I have a repeated measure experiment (pre, post intervention), and I would like to test for changes induced by the intervention. When I test, even at near 0 treshold, I don't get any results. Hence I would like to validate my design matrix and exchange blocks (which I don't fully understand). Any suggestions welcome!


I have set up my files in alphanumerical order : 


aXXX01-pre.txt
aXXX02-pre.txt
aXXX03-pre.txt
bXXX01-post.txt
bXXX02-post.txt
bXXX03-post.txt
...

My design matrix is comprised of one column per subject, and a contrast column :

1 0 0 1
0 1 0 1
0 0 1 1
1 0 0 -1
0 1 0 -1
0 0 1 -1

Contrast = [ 0, 0, 0, 1] / or [1, zeros(1, nsub)]; (tried both ways)

Exchange bloacks = [ 1 2 3 4 1 2 3 4 ]
This is the part where I am not sure what it does!
I have tried, like in some exmples, to specify it as [1;2;3;4;1;2;3;4], and as reshape(repmat(1:nsub, 1, 2), 1, []);
In the last two cases, I get 'exchange blocks : no' in the output.

In all cases, even at very low T, I get no results. Thanks for letting me know if I did it the right way (and that there is no results in these data).



Great thanks,


Dylan


 

Feb 28, 2024  12:02 AM | Andrew Zalesky
RE: Repeated measures (2) t-test validation

Hy Dylan, 


the design matrix and exchange blocks look fine to me. Simply using  [ 1 2 3 4 1 2 3 4 ]  for exchange blocks should be fine. 


You may also want to test the opposite contrast of [ 0 0 0 -1]. Currently it seems that you are only testing one direction of difference. 


Not being able to reject the null hypothesis is a result. 


Andrew


 


Originally posted by dylan sutterlin:



Hi,


I have a repeated measure experiment (pre, post intervention), and I would like to test for changes induced by the intervention. When I test, even at near 0 treshold, I don't get any results. Hence I would like to validate my design matrix and exchange blocks (which I don't fully understand). Any suggestions welcome!


I have set up my files in alphanumerical order : 


aXXX01-pre.txt
aXXX02-pre.txt
aXXX03-pre.txt
bXXX01-post.txt
bXXX02-post.txt
bXXX03-post.txt
...

My design matrix is comprised of one column per subject, and a contrast column :

1 0 0 1
0 1 0 1
0 0 1 1
1 0 0 -1
0 1 0 -1
0 0 1 -1

Contrast = [ 0, 0, 0, 1] / or [1, zeros(1, nsub)]; (tried both ways)

Exchange bloacks = [ 1 2 3 4 1 2 3 4 ]
This is the part where I am not sure what it does!
I have tried, like in some exmples, to specify it as [1;2;3;4;1;2;3;4], and as reshape(repmat(1:nsub, 1, 2), 1, []);
In the last two cases, I get 'exchange blocks : no' in the output.

In all cases, even at very low T, I get no results. Thanks for letting me know if I did it the right way (and that there is no results in these data).



Great thanks,


Dylan


 



 

Feb 29, 2024  12:02 PM | dylan sutterlin - university of montreal
RE: Repeated measures (2) t-test validation

Hi ,


Thank you for this quick and helpful response/validation (and for a reminder that indeed not rejecting null hyp. is informative at some point)!


Can you explain what the exchange blocks do? I just realize that I used the example [1 2 3 4], but with only 3 participants in my example, so I am a bit confused about its usage. Let's say that my final design matrix has 60 rows (cond a x sub00-sub30 and cond. b x sub00-sub30; like the example above), and 31 columns (1/sub + the contrast one).


Then would the exchange block look like : [1 2 3 4 5 ...30 1 2 3 4 5 ... 30] ? 


Thank you very much,


Dylan

Mar 1, 2024  04:03 AM | Andrew Zalesky
RE: Repeated measures (2) t-test validation

Exchange blocks enable you to constrain permutations to occur within a group of observations, such as repeat measurments within the same individual.


There is an explanation of their use in the NBS manual. 


Originally posted by dylan sutterlin:



Hi ,


Thank you for this quick and helpful response/validation (and for a reminder that indeed not rejecting null hyp. is informative at some point)!


Can you explain what the exchange blocks do? I just realize that I used the example [1 2 3 4], but with only 3 participants in my example, so I am a bit confused about its usage. Let's say that my final design matrix has 60 rows (cond a x sub00-sub30 and cond. b x sub00-sub30; like the example above), and 31 columns (1/sub + the contrast one).


Then would the exchange block look like : [1 2 3 4 5 ...30 1 2 3 4 5 ... 30] ? 


Thank you very much,


Dylan



 

Mar 2, 2024  02:03 PM | dylan sutterlin - university of montreal
RE: Repeated measures (2) t-test validation

Thank you for the precision!


 


Best,


Dylan