-- Hello,
I have a number of questions about higher level analyses and their
interpretation when using additional covariates to model for behavioural
factors.
(1) Is it possible to control for an additional covariate that I am not
interested in but suspect to have an influence on the outcome of the
experiment (like measures of intelligence)? By modelling all of them as
an additional EV? Or by making it one per subject (like when allowing
for individual differences in variance)?
(2) If I want to know whether there is a negative correlation between my
additional covariate (modelled as a separate EV) and the data, do I need
to set the contrast to -1?
(3) Having used an additional covariate (like the RT example in the
webpages) and using that precise contrast, what does the result mean?
I'm unclear on whether the brain area correlates both with RT and the
task itself, or whether the level activity in that area somehow reflects
RT, potentially independent of the task. Can I distinguish between those
two cases, or make sure that my contrast reflects 'correlation with
EV, given the task'?
I hope this makes sense. Thanks for any help.
Amande Pauls
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Amande Pauls
University Laboratory of Physiology, Oxford, UK
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