-----Original Message-----
From: Iain Hamlin [mailto:iain.hamlin at strath.ac.uk]
Sent: Tuesday, 27 February, 2018 14:35
To: Viechtbauer Wolfgang (SP); ???; r-sig-meta-analysis at r-project.org
Subject: RE: [R-meta] Meta-analysis of ANOVA interaction effects
Dear Kyungnam and Wolfgang,
Kyungnam, thanks for the link, and, Wolfgang, thanks for clarifying that
the link actually relates to the interaction of moderators in meta-
regression, rather than ANOVA interaction effects.
It had similarly been suggested to me by someone else that I treat the
interaction effect as the difference between the two mean difference
scores. However, I was ? and still am ? unsure as to how I can use r to
perform the meta-analysis. Does one simply meta-analyse the pairs of mean
difference scores in a similar way to the most basic meta-analyses which
meta-analyse the differences between pairs of means?
Kind regards,
Iain
-----Original Message-----
From: Viechtbauer Wolfgang (SP)
[mailto:wolfgang.viechtbauer at maastrichtuniversity.nl]
Sent: 27 February 2018 12:02
To: ??? <fstyle71 at naver.com>; Iain Hamlin <iain.hamlin at strath.ac.uk>;
r-sig-meta-analysis at r-project.org
Subject: RE: [R-meta] Meta-analysis of ANOVA interaction effects
The URL links to a discussion of how to examine the interaction between
two moderators in a meta-regression model. Iain is asking about how to
meta-analyze interaction effects directly. That's not the same issue.
Iain - the interaction in a 2x2 ANOVA is the difference between two
simple effects. So, for factors A and B, each with two levels, this is:
(mean_A1 - mean_A2) - (mean_B1 - mean_B2)
or equivalently
(mean_A1 - mean_B1) - (mean_A2 - mean_B2)
If needed (because studies use different scales), one can standardize
this based on sqrt(MSE) of the model (MSE = mean squared error).
In fact, it isn't difficult to show that the t-test for the interaction
is directly related to this standardized interaction effect:
((mean_A1 - mean_A2) - (mean_B1 - mean_B2)) / sqrt(MSE) = t * sqrt(1/n_A1
+ 1/n_A2 + 1/n_B1 + 1/n_B2)
If all studies use the same scale, then I would recommend to meta-analyze
the unstandardized interaction effects; otherwise go with the
standardized ones.
Best,
Wolfgang
-----Original Message-----
From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bounces at r-
project.org] On Behalf Of ???
Sent: Tuesday, 27 February, 2018 2:22
To: Iain Hamlin; r-sig-meta-analysis at r-project.org
Subject: Re: [R-meta] Meta-analysis of ANOVA interaction effects
Dear Lian,
Wolfgang's web site for the metafor package has an example with
detailed explanations for interaction effects.
You can find the information in the following URL.
http://www.metafor-
project.org/doku.php/tips:multiple_factors_interactions
Kyungnam
-----Original Message-----
From: "Iain Hamlin"<iain.hamlin at strath.ac.uk>
To: "r-sig-meta-analysis at r-project.org"<r-sig-meta-analysis at r-
project.org>;
Cc:
Sent: 2018-02-27 (?) 03:38:48
Subject: [R-meta] Meta-analysis of ANOVA interaction effects
Dear all,
Using r to do a meta-analysis of differences between means looks
simple, even for an r novice like me. However, I can find worryingly
little information - in books or on the internet - about how to use r
to meta- analyse the interaction effects stemming from 2X2 ANOVAs.
I would be very grateful if someone could provide me with, or point me
in the direction of, information on how to do this in r.
Many thanks,
Iain