R MatchIt() with ratio>1 and caliper=0.1
<p>R version 3.1.1 (2014-07-10)
MatchIt version 2.4-21 (2013-06-27)</p>

<p>I am using the <code>MatchIt()</code> package in R to 2:1 propensity score match my <code>control</code> and <code>treatment</code> groups. However, when I apply the <code>caliper</code> argument to the function, it allows 1:1 matches to occur, such that my final matched cohorts are not 2:1 matched. For example, if I start with 80 treatment and 200 control units, my matched cohort may then be 62 treatment and 94 control units (rather than 124 control units).</p>

<p>Is there a way to force the <code>ratio</code> argument to override the <code>caliper</code> argument, thereby only retaining treatment units for which there are at least 2 matched control units? (ie. I would like to discard treatment units that have only 0 or 1 matched control units within the specified caliper). </p>

<p>My function call is below:</p>

<pre><code>m.out &lt;- matchit(treat ~ x1 + x2, data=data, method = "nearest", discard = "both", 
caliper = 0.1, ratio = 2)
</code></pre>