[R] Package or function for selecting matched pairs?

[Ista Zahn]

David, this is very nice. Simple and straightforward. Thank you!
-Ista

On Wed, Feb 17, 2010 at 10:09 AM, David Winsemius
<dwinsemius at comcast.net> wrote:
>
> On Feb 17, 2010, at 8:55 AM, David Winsemius wrote:
>
>>
>> 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$grps), ]
>>  course level size rating               grps   # forgot to relabel
>> 2      b   100   12      5   100.(0,15].(4,6]
>> 1      a   100   44      4  100.(35,60].(2,4]
>> 3      c   200   23      5  200.(15,35].(4,6]
>> 5      e   200   30      5  200.(15,35].(4,6]
>> 4      d   300  124      3 300.(60,150].(2,4]
>>
>
> I got an offlist request to explain this. I see that I fail to properly edit
> it so that the 5th column was named "grps". I had run the function
> originally to create ED$cuts, but thought that variable might be better
> called "grps" so edited the functions but failed to edit the output. If the
> question what how it works, then:
>
> A) create grouping categories for each variable. I applied my domain
> knowledge to decide that levels ought to be "ungrouped" but that size and
> rating would be groups in categories that were determiend by the breaks
> argument to the cut functions.
> B) paste the together with a "." period separator to create "grps" that
>  would be considered similar. This I believe is "blocking" in anova
> terminology and perhaps "strata" in regression terminology. The category
> labels become just parts of the bigger character string.
>
> --
> David.
>
>
>>>
>>> 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
>>>
>>> ______________________________________________
>>> R-help at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide
>>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>
>> David Winsemius, MD
>> Heritage Laboratories
>> West Hartford, CT
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> David Winsemius, MD
> Heritage Laboratories
> West Hartford, CT
>
>



-- 
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org