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>