title: Combine two plots created with effects package in R
body: <p>I have the following Problem. After running an ordered logit model, I want to R's effects package to visualize the results. This works fine and I did so for two independent variables,  then I tried to combine the two plots. However, this does not seem to work. I provide a little replicable example here so you can see my problem for yourself:</p>
  
  <pre><code>library(car)
  data(Chile)
  mod &lt;- polr(vote ~ age + log(income), data=Chile)
  
  eff &lt;- effect("log(income)", mod)
  plot1 &lt;- plot(eff, style="stacked",rug=F, key.args=list(space="right"))
  
  eff2 &lt;- effect("age", mod)
  plot2 &lt;- plot(eff2, style="stacked",rug=F, key.args=list(space="right"))
  </code></pre>
  
  <p>I can print these two plots now independently, but when I try to plot them together, the first plot is overwritten. I tried setting <code>par(mfrow=c(2,1))</code>, which didn't work. Next I tried the following:</p>
  
  <pre><code>print(plot1, position=c(0, .5, 1, 1), more=T)
  print(plot2, position=c(0,0, 1, .5))
  </code></pre>
  
  <p>In this latter case, the positions of the two plots are just fine, but still the first plot vanishes once I add the second (or better, it is overwritten). Any suggestions how to prevent this behavior would be appreciated.</p>