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help > RE: Examining carryover/order effects in a cross-over design
Dec 3, 2018 01:12 PM | Yuval Argaman
RE: Examining carryover/order effects in a cross-over design
Dear all,
Given that I have a carryover effect in some of my seeds - I decided to add a 2nd-level covariate that accounts for order: it codes 1 for each participant that had the real treatment administered first, and 0 otherwise.
Is this considered as a viable approach for controlling for order in such an experiment?
Thanks in advance,
Yuval.
Originally posted by Yuval Argaman:
Given that I have a carryover effect in some of my seeds - I decided to add a 2nd-level covariate that accounts for order: it codes 1 for each participant that had the real treatment administered first, and 0 otherwise.
Is this considered as a viable approach for controlling for order in such an experiment?
Thanks in advance,
Yuval.
Originally posted by Yuval Argaman:
Dear Alfonso and CONN community,
I'm analyzing the resting-state data from my study, in which each participant underwent 2 scans X 2 conditions.
This means that I my conditions are: Pre_Real, Pre_Sham, Post_Real, and Post_Sham.
Accordingly, I defined my repeated-measures ANOVA: AllSubjects [1], and Pre_Real, Pre_Sham, Post_Real, Post_Sham [-1 1 1 -1] (as specified in the CONN manual, p.26).
However, I have a reason to suspect that there might be a carryover effect. Therefore, I decided to perform a paired t-test, comparing only the Pre_Real and Pre_Sham, so I selected only the 2 of them and defined the contrast as [-1 1]. Here, I got some significant results (which is a cause for concern)
Additionally, I have a reason to believe that controlling for the order in which the participants received their treatments - would neutralize the order effect.
To this end, I defined the order effect using 2 second-level dichotomous covariates - Real_first and Sham_first, which are the opposite of each other. I'm not sure that this is the way to do it, though.
Given the experimental design's within-subject nature, I'd like to ask the following questions:
1. Did I define the carryover effect test correctly? or should I instead use the contrast Pre_Real, Pre_Sham, Post_Real, Post_Sham [-1 1 0 0]?
2. How should I define the order effect in order to check for its influence and possible association with the carryover effect?
Sorry for the long post and thanks in advance,
Subtly,
Yuval.
I'm analyzing the resting-state data from my study, in which each participant underwent 2 scans X 2 conditions.
This means that I my conditions are: Pre_Real, Pre_Sham, Post_Real, and Post_Sham.
Accordingly, I defined my repeated-measures ANOVA: AllSubjects [1], and Pre_Real, Pre_Sham, Post_Real, Post_Sham [-1 1 1 -1] (as specified in the CONN manual, p.26).
However, I have a reason to suspect that there might be a carryover effect. Therefore, I decided to perform a paired t-test, comparing only the Pre_Real and Pre_Sham, so I selected only the 2 of them and defined the contrast as [-1 1]. Here, I got some significant results (which is a cause for concern)
Additionally, I have a reason to believe that controlling for the order in which the participants received their treatments - would neutralize the order effect.
To this end, I defined the order effect using 2 second-level dichotomous covariates - Real_first and Sham_first, which are the opposite of each other. I'm not sure that this is the way to do it, though.
Given the experimental design's within-subject nature, I'd like to ask the following questions:
1. Did I define the carryover effect test correctly? or should I instead use the contrast Pre_Real, Pre_Sham, Post_Real, Post_Sham [-1 1 0 0]?
2. How should I define the order effect in order to check for its influence and possible association with the carryover effect?
Sorry for the long post and thanks in advance,
Subtly,
Yuval.
Threaded View
| Title | Author | Date |
|---|---|---|
| Yuval Argaman | Nov 6, 2018 | |
| Yuval Argaman | Dec 3, 2018 | |