if you don't expect a trend, I would average the four (or two)
pre-test scores, and the four (two) post-test scores, and then do a
repeated measures t-test.
If you expect some sort of consistent trend that you need to remove
then you need to do something like a multilevel model.
Jeremy
On 26 October 2010 14:44, Davies, Nicola <[log in to unmask]> wrote:
> Hi,
>
> Does anyone know which statistical test I would need for the following:
>
> I have two independent groups: One group is before the service redesign; The second group is after the service redesign. Both groups will provide data at 4 points in time over a 12-month period.
>
> I need to know the statistical test I will use in order to calculate how many participants I need per group (I am using Gpower to do this).
>
> I will be trying to determine differences between the groups.
>
> Thank you for your help,
>
> Nicola
>
--
Jeremy Miles
Psychology Research Methods Wiki: www.researchmethodsinpsychology.com
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