Hi-<div>You need to enter in treatment variable as a factor, then indicate the contrast you want to estimate things for using the <span class="Apple-style-span" style="font-family:arial,sans-serif;font-size:13px;border-collapse:collapse;color:rgb(34,34,34)">treat.value and control.value arguments. In R you don't want to enter them in as dummy variables. This seems to work fine on our side.</span></div>
<div><font class="Apple-style-span" color="#222222" face="arial, sans-serif"><span class="Apple-style-span" style="border-collapse:collapse">best,</span></font></div><div><font class="Apple-style-span" color="#222222" face="arial, sans-serif"><span class="Apple-style-span" style="border-collapse:collapse">Dustin</span></font></div>
<div><font class="Apple-style-span" color="#222222" face="arial, sans-serif"><span class="Apple-style-span" style="border-collapse:collapse"><br clear="all"></span></font>Dustin Tingley<br>Government Department<br>Harvard University<br>
<a href="http://scholar.harvard.edu/dtingley" target="_blank">http://scholar.harvard.edu/dtingley</a><br>
<br><br><div class="gmail_quote">On Thu, Jan 26, 2012 at 10:18 AM, Heymans, M.W. <span dir="ltr"><<a href="mailto:mw.heymans@vumc.nl">mw.heymans@vumc.nl</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<p>Dear list,</p>
<p> </p>
<p>Is it possible to do a mediation analysis in combination with an independent categorical (dummy)variable, something like this? How to calculate the mediation effect with respect to both dummy variables? Just include dummy1 first andf than dummy2 in model
c? I tried it with real data but the code below does not work? What is wrong? (define the variable as factor also does not solve it)</p>
<p> </p>
<p><font face="Courier New"># Model 1<br>
a <- glm(indep ~ dummy1 + dummy2, data=x, family=gaussian) <br>
b <- glm(mediator ~ dummy1 + dummy2, data=x, family=gaussian)<br>
c <- glm(indep outcome~ dummy1 + dummy2 + mediator, data=x, family=gaussian)</font></p>
<p><font face="Courier New">a<br>
b <br>
c<br>
<br>
med1.boot <- mediate(b, c, boot=TRUE, sims=1000, treat=c("dummy1", "dummy2"), mediator="mediator")<br>
summary(med1.boot)</font></p>
<p><font face="Courier New"></font> </p>
<p><font face="Courier New">Thanks for the response.</font></p>
<p><font face="Courier New"></font> </p>
<p><font face="Courier New">kind regards,</font></p>
<p><font face="Courier New"></font> </p>
<p><font face="Courier New">Martijn</font></p>
<p><font face="Courier New"></font> </p>
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