Hi,
The restriction is that no linear combination of the columns sum to
a column of ones. first_utils demeans the design matrix such that the
first column of the design matrix is all ones. This is why splitting the
groups into into multiple columns causes an error. first_utils will demean
all
regressors internally.
Cheers,
Brian
> ok, the preliminary problem .. i needed to use 1 EV with 1 or -1 for the
> group difference.
>
> apparently the group difference needed to be in 1 ev and not multiple
> evs, but how would you add an additional regressor if you can only use
> 1 EV?
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