Dear all,
When performing meta-regression analysis, I use this code to change
turn a variable into a factor:
dat$duration <- relevel
<http://stat.ethz.ch/R-manual/R-devel/library/stats/html/relevel.html>(factor
<http://stat.ethz.ch/R-manual/R-devel/library/base/html/factor.html>(dat$duration),
ref="S")
In my data, the duration moderator has four values including S
(short), M (medium), L (long), and NA (not provided). And I tried to figure
out the interaction between this moderator and another moderator named
"Posttest type" with two values of M (meaning) and U (use). The problem I
face now is that with different ference I used, the coefficiency will
differ, for example,
(a) I use M as reference for duration, and this is the result
estimate se zval pval
ci.lb ci.ub
durS:posU 2.3309 0.8690 2.6824 0.0073 0.6278 4.0341 **
(b) I use N/A as reference for duration, and this is the result
estimate
se zval pval ci.lb ci.ub
durS:posU 1.7890 1.4294 1.2516 0.2107 -1.0126 4.5906
(c) I use L as reference for duration, and this is the result
estimate se zval
pval ci.lb ci.ub
durS:posU 1.2827 0.9275 1.3829 0.1667 -0.5352 3.1005
So, eventually, which one should I choose to be the final result? Is
there any criteria to choose between the three?
Nick
??? (Nick Chen)
Email: t571 at wlgsh.tp.edu.tw <t5741 at wlgsh.tp.edu.tw>
[R-meta] About choosing the reference
2 messages · 英文科陳品誠, Wolfgang Viechtbauer
Dear Nick, Please do not post in HTML format. See what this can do to posts -- makes things quite unreadable. See also the notes on the mailing list page: https://stat.ethz.ch/mailman/listinfo/r-sig-meta-analysis All of these results just reflect different contrasts of the same two-way interaction. So there is not one that is inherently preferable. This is not an issue specific to meta-analysis. You would face the same issue in any regression model with such a two-way interaction. If the two-way interaction as a whole is significant (based on a test of all three interaction terms, so the chi^2- or F-test with df=3), then one could examine four simple contrasts (between M and U of pos for each of the four levels of dur). Best, Wolfgang
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From: R-sig-meta-analysis <r-sig-meta-analysis-bounces at r-project.org> On Behalf
Of ?????? via R-sig-meta-analysis
Sent: Thursday, December 14, 2023 15:10
To: r-sig-meta-analysis at r-project.org
Cc: ?????? <t571 at wlgsh.tp.edu.tw>
Subject: [R-meta] About choosing the reference
Dear all,
When performing meta-regression analysis, I use this code to change
turn a variable into a factor:
dat$duration <- relevel
<http://stat.ethz.ch/R-manual/R-devel/library/stats/html/relevel.html>(factor
<http://stat.ethz.ch/R-manual/R-
devel/library/base/html/factor.html>(dat$duration),
ref="S")
In my data, the duration moderator has four values including S
(short), M (medium), L (long), and NA (not provided). And I tried to figure
out the interaction between this moderator and another moderator named
"Posttest type" with two values of M (meaning) and U (use). The problem I
face now is that with different ference I used, the coefficiency will
differ, for example,
(a) I use M as reference for duration, and this is the result
estimate se zval pval
ci.lb ci.ub
durS:posU 2.3309 0.8690 2.6824 0.0073 0.6278 4.0341 **
(b) I use N/A as reference for duration, and this is the result
estimate
se zval pval ci.lb ci.ub
durS:posU 1.7890 1.4294 1.2516 0.2107 -1.0126 4.5906
(c) I use L as reference for duration, and this is the result
estimate se zval
pval ci.lb ci.ub
durS:posU 1.2827 0.9275 1.3829 0.1667 -0.5352 3.1005
So, eventually, which one should I choose to be the final result? Is
there any criteria to choose between the three?
Nick
??? (Nick Chen)
Email: t571 at wlgsh.tp.edu.tw <t5741 at wlgsh.tp.edu.tw>