Posted by
Mike on
Mar 18, 2011; 2:09pm
URL: http://spssx-discussion.165.s1.nabble.com/Cell-sizes-Orthoplan-tp3964555p3969350.html
If you're going to treat this as a 2-way independent groups ANOVA
then you should be asking what is the minimum level of power do you
need to detect a significant 2-way interaction. The main effects will
have higher levels of power relative to the interaction. So, one focus
to have is what are the effect sizes you're trying to detect, especially
in the 2-way interaction? If the effect sizes are large, then a small number
of subjects are needed. If the effect sizes are small, the a large number
of subjects will be needed. It is best if you use one of the statistical
power packages to examine what happens in your situation when you
vary (a) sample size, (b) effect size, and (c) level of statistical power
(assuming you're using an alpha = 0.05).
-Mike Palij
New York University
[hidden email]
----- Original Message -----
From: "Lea" <
[hidden email]>
To: <
[hidden email]>
Sent: Friday, March 18, 2011 5:32 AM
Subject: Cell sizes Orthoplan
> Dear All,
>
> I would be very glad if somebody might help me with the following question -
>
> I need to conduct a factorial survey (a.k.a vignette study).
>
> - There are 2 factors A and B.
>
> - Factor A has 4 conditions, B has 5 conditions.
>
> - It is a between-subjects ANOVA design.
>
> I now want to gauge the minimum number of person needed for this study.
> This is of course a question of test power, but my problem relates to a
> rather specific aspect, namely:
>
> The total number of cells would be 4*5=20.
>
> However, should I consider the number of people per condition within each
> factor (that would be 4 respectively 5)OR the number of people across all
> possible combinations (the 4*5 = 20 cells) to gauge the sample size needed?
>
> Obviously, even if one follows the rule of thumb of "use 25 obersvations
> per cell", the conclusions would be quite different, because then I would
> either had to use 4*25 = 100 respectivley 5*25 =125 people, or 20*25= 500
> people
>
> What would be the appropriate view here?
>
> Many thanks for your ideas!!!!
> Lea
>
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