Dear Elizabeth,
As ALex Leff says, you can compare your studies using either fixed or
random effect models. Random effects is required to make inferences about
differences in activation but you need to have a minimum of 10-12 subjects
in each group.
Fixed effect models are useful for identifying common activations in the
different studies but are likely to overestimate differences between studies.
Best wishes
Cathy
> Dear SPMers
> I've recently become interested in comparing the results of 2 different
> PET studies.
>
> The studies used the same type of tasks (lexical decision and semantic
> categorization) but differed on a number of parameters including number
> of conditions, timing, number of subjects.
>
> I was under the impression that in order to compare these two different
> studies I must use a random effects analysis.
> However, I have noticed that some people conduct a fixed effects
> MetaAnalysis to compare 2 or more studies.
>
> Can anyone tell me which method (if either) is preferable? What are the
> benefits and weaknesses of these 2 methods?
>
> Many thanks
>
> ************************************************
> Elizabeth Dick
> Centre for Speech and Language
> Dept. of Experimental Psychology
> Cambridge University
> Downing Street, Cambridge, CB2 3EB
>
> Email: [log in to unmask]
> Tel: (01223) (7)66451
> ************************************************
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