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help > RE: Entering 2nd level covariates
Jul 2, 2014 11:07 PM | Alfonso Nieto-Castanon - Boston University
RE: Entering 2nd level covariates
Hi Eileen,
The frame-wise displacement values (one value per sample/scan characterizing the subject movement between two consecutive scans) are typically entered as 'first-level covariates', or perhaps more commonly you would enter the movement parameters (e.g. rp_*.txt obtained during SPM realignment), and then select an additional 'first-derivative' term to compute in addition the scan-to-scan movement effects. Second-level covariates are meant to identify subject-level variables instead. You can easily aggregate some of your first-level covariates (right-click on the Setup.first-levelCovariates list) to obtain, for example, the maximum absolute frame-wise displacement across all samples/scans for each subject, and then use these new second-level covariate (subject-level descriptors) in your second-level analyses to potentially correct for between-subject differences in the amount/severity of movement. Let me know if this is answering your question or if I am misinterpreting or missing something here.
Best
Alfonso
Originally posted by Eileen Persichetti:
The frame-wise displacement values (one value per sample/scan characterizing the subject movement between two consecutive scans) are typically entered as 'first-level covariates', or perhaps more commonly you would enter the movement parameters (e.g. rp_*.txt obtained during SPM realignment), and then select an additional 'first-derivative' term to compute in addition the scan-to-scan movement effects. Second-level covariates are meant to identify subject-level variables instead. You can easily aggregate some of your first-level covariates (right-click on the Setup.first-levelCovariates list) to obtain, for example, the maximum absolute frame-wise displacement across all samples/scans for each subject, and then use these new second-level covariate (subject-level descriptors) in your second-level analyses to potentially correct for between-subject differences in the amount/severity of movement. Let me know if this is answering your question or if I am misinterpreting or missing something here.
Best
Alfonso
Originally posted by Eileen Persichetti:
Hi Alfonso,
I am working with a 26 subject pre/post design and I am wondering how I would go about entering the second level covariates. Initially I had entered nothing for first level and frame-wise displacement1 and frame-wise displacement2 for the second level, one for each session. Is this the correct way to enter the second level covariate?
Thanks,
Eileen
I am working with a 26 subject pre/post design and I am wondering how I would go about entering the second level covariates. Initially I had entered nothing for first level and frame-wise displacement1 and frame-wise displacement2 for the second level, one for each session. Is this the correct way to enter the second level covariate?
Thanks,
Eileen
Threaded View
| Title | Author | Date |
|---|---|---|
| Eileen Persichetti | Jul 2, 2014 | |
| Alfonso Nieto-Castanon | Jul 2, 2014 | |
| Eileen Persichetti | Jul 3, 2014 | |
| Julia Landsiedel | Jul 3, 2014 | |
| Eileen Persichetti | Jul 3, 2014 | |
| Julia Landsiedel | Jul 3, 2014 | |
| Eileen Persichetti | Jul 3, 2014 | |
| Julia Landsiedel | Jul 3, 2014 | |
| Alfonso Nieto-Castanon | Jul 5, 2014 | |