Hi Shary,
I think this is dodgy, but (I hope you don't mind) I've CCed the list
to get other opinions...
I seem to remember seeing something very similar (e.g. using a cohort
of controls to give a z-score to an individual subject) but I can't
remember the reference off the top of my head, and having failed to
find it on my first page of Google Scholar results, I'm afraid I'll
leave you to look ;-)
The reason I think it's a bad idea, is because Salmond et al found
that unbalanced group sizes made the analysis very fragile to
non-Gaussianity etc. Since a group with a single subject is as
unbalanced as you can get, it seems possibly that you might get many
false positives from only a slight departure from Gaussianity. But I'm
not expert, so see what other people have to say...
http://dx.doi.org/10.1016/S1053-8119(02)91153-5
Best,
Ged.
P.S. I think you're right about your interpretation of the conjunction
null below.
Shahryar (Shary) Rafi-Tari wrote:
> Hi Ged,
>
> I have a question about comparing one subject (patient) with a a group
> of controls (n=20). Here are the questions:
>
> 1. Can I do t-test with the one patient in group 1 and the 20 healthy in
> grouop 2?
>
>
> 2. If I needed to compare three groups: group 1 with n=1 , group 2 with
> n=1 and group 3 n=20. Groups 1 and 2 are made of one patient each.
> Group 3 is made of healthy controls. In this case can I simply do full
> factorial (one factor with 3 levels and three cells). Then, I do
> conjunction null available in SPM5. If I find a region of difference
> between the two patients and the controls, I can say that there is a
> significant difference and overlaping areas of differences between these
> two patients and the controls.
>
>
> 3. Do you know of any good reference for the comparison of single
> subject and a group of subjects?
>
>
> Thanks,
> Shary
>
>
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