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Hi Ciara

First, remember that power analysis is "Guessing, masquerading as mathematics".

You take a guess at what the effects might be, and then you try to the sample size that would give you that effect.

You don't know what the effects will be, because you haven't done the research yet.

In summary, it's OK to assume a medium effect.  But if you don't get a significant result, it might be because the effect was small.

Jeremy




On 3 February 2014 11:03, Ciara gill <[log in to unmask]> wrote:
Hey everyone,

I was just wondering if anyone could provide advice on determining sample size for conducting a mediation using product of coefficent approach and bootstrapping. I have the Fritz and MacKinnon paper and have consulted the table at the back but am not feeling at all confident. It notes  having a value for each of the effect paths and I just wanted to ensure that you calculate this from prior research. As I am connecting slightly altered variables to what has been previously explored I dont have previous literature for effect size - is it appropriate to assume a medium effect?

Apologies if this is not clear, first gander into this type of analysis

Ciara