[R] Package or function for selecting matched pairs?

[David Winsemius]

On Feb 17, 2010, at 8:26 AM, Ista Zahn wrote:

> Hi all,
> I am designing a study in which I am selecting a subset of college
> courses to be randomly assigned to one of two conditions. I would like
> to create matched pairs of courses, and then randomly assign them to
> condition within each pair. I would like to identify, for each course,
> the one that best matches it, and quantify how well it matches. Here
> is a much simpler data set for purposes of illustration:
>
> ED <- data.frame(course = letters[1:5], level=factor(c(100, 100, 200,
> 300, 200)), size = c(44, 12, 23, 124, 30), rating = c(4,5,5,3,5))
>
>>>  course level size rating
> 1      a   100   44      4
> 2      b   100   12      5
> 3      c   200   23      5
> 4      d   300  124      3
> 5      e   200   30      5

 > ED$grps <- paste(ED$level, cut(ED$size,  
breaks=c(0,15,35,60,150,300)),
+ cut(ED$rating, breaks=c(0,2,4,6)), sep=".")

 > ED[order(ED$grps), ]
   course level size rating               cuts
2      b   100   12      5   100.(0,15].(4,6]
1      a   100   44      4  100.(35,60].(2,4]
3      c   200   23      5  200.(15,35].(4,6]
5      e   200   30      5  200.(15,35].(4,6]
4      d   300  124      3 300.(60,150].(2,4]

>
> Basically I want a function that tells me that courses c and e "match"
> so that I can treat them as a pair and randomly assign them to
> condition. I've looked at the matching and MatchIt packages, but they
> seem to need to know in advance which course is in the treatment
> condition and which is in the control condition. I'll be grateful for
> any suggestions.
>
> Best,
> -- 
> Ista Zahn
> Graduate student
> University of Rochester
> Department of Clinical and Social Psychology
> http://yourpsyche.org
>
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT