Hi - no there is no problem with having different group sizes here,
everything should be accurate.
Cheers.
On 29 Mar 2009, at 02:27, Yi-Shin Sheu wrote:
> Dear FSL experts,
>
> I am doing a two-sample t-test group comparison using 20 patients
> and 60
> controls, and would like to use randomise to do permutation test as to
> derived corrected p value statistical maps.
>
> I read on the FSL official website for randomise, it stated " .....
> For
> large sample sizes, with 50-100 or more degrees of freedom, the P-
> values
> should be highly accurate. When the sample size is low and there are
> many
> nuisance regressors, accuracy could be a problem."
>
> My group size is large (N=80), however, it consists of relatively
> small
> number (N=20) of patient and a relatively large number (N=60) of
> control.
> Will the discrepancy in group size lead to serious statistical
> problems?
> Will that be a better idea if I only pick those controls who are
> best match
> to patients, to reduce the groups size differences and obviate the
> need to
> use nuisance covariates.
>
> Thank you in advance for your help.
>
> Best,
>
> Yi-Shin
>
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Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
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