I have a similar case in which a participant got once a placebo and once a drug and then did two tasks [high and low]. The explanation here was very helpful in creating a design matrix, so thank you very much! My study has 32 participants and since every participant has 4 matrices, I created a 128x34 matrix. The first column codes drug, the second highVSlow and the rest indicate to which participants they belong. So the first 4 files belonging to subject1 would look like this:
Sub1PH 0 1 1 0 0 ...
Sub1PL 0 0 1 0 0 ...
Sub1DH 1 1 1 0 0 ...
Sub1DL 1 0 1 0 0 ...
The permutation blocks would then look like this [1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, ...]
is this correct? (also see attachment)
However, 3 things are unclear cause they seem to contradict other posts in this forum:
- In other posts a column with only ones is additionally included
to indicate a global mean. Why is this column here
omitted?
- Similar to the post above, I encoded drug: 0 for placebo and 1
for drug. Why do other posts recommend 1 and -1? I guess there is a
difference but I could not figure it out...
- When I am interested in the contrast for
main effect drug = [1 0 0 0 ..] and for the decrease [-1 0
0 0]
main effect task = [0 1 0 0 .. ] (I guess this means high > low
right?)
I would run a t-test, right? And since I explore both drug > placebo [1 0 0 0 ..] and placebo > drug [-1 0 0 0], I would need to half the significance to 0.025 to compensate for testing twice, right? Or would I actually need to divide alpha by 4 since I run both contrasts for both main effects to safeguard against alpha error accumulation?
Thank you so much for your help!
Cheers,
Max
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Title | Author | Date |
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David de Wide | Aug 3, 2017 | |
Max Kathofer | Oct 31, 2024 | |
Andrew Zalesky | Nov 1, 2024 | |
Max Kathofer | Nov 1, 2024 | |
Andrew Zalesky | Nov 1, 2024 | |
yue zhang | Jan 11, 2020 | |
Andrew Zalesky | Aug 5, 2017 | |
Liam Nestor | Sep 27, 2019 | |
Andrew Zalesky | Sep 28, 2019 | |
Liam Nestor | Sep 28, 2019 | |
Andrew Zalesky | Sep 28, 2019 | |
Liam Nestor | Sep 30, 2019 | |
Andrew Zalesky | Oct 1, 2019 | |
Liam Nestor | Oct 1, 2019 | |
David de Wide | Aug 6, 2017 | |
Andrew Zalesky | Aug 7, 2017 | |
David de Wide | Aug 7, 2017 | |
Andrew Zalesky | Aug 7, 2017 | |
David de Wide | Aug 11, 2017 | |
Andrew Zalesky | Aug 12, 2017 | |
David de Wide | Aug 18, 2017 | |
Andrew Zalesky | Aug 19, 2017 | |