I still am not sure what we are supposed to put in the "formula" field of
Matchit when we input the argument distance=propensityscores. Do I still input the
covariates (i.e. D~X1+X2...)? Or is it formula= D~propensityscores?
-Abigail
From: gov2001-l-bounces at
mailman.fas.harvard.edu [mailto:gov2001-l-bounces at
mailman.fas.harvard.edu] On Behalf Of Miya Woolfalk
Sent: Wednesday, April 15, 2009 11:11 AM
To: gov2001-l at
lists.fas.harvard.edu
Subject: [gov2001-l] important clarification to ps 8 question 3
Hi,
Given the confusion, I wanted to clarify what we want for question 3.
Essentially, we want to make sure that you all understand the logic behind propensity
score matching. This is why we ask you to calculate the propensity score independent of
the matchit() function. The key point of the wording in question 3 is that your call to
matchit() should use the propensity scores that you estimate outside of matchit() to
conduct the matching. In other words, no matter how you write the formula in matchit(),
the propensity scores that you estimate outside of matchit() should be the distance metric
used in matching. I alluded to this in a few of the prior emails about this question and
apologize if I was being too elusive.
Miya
--
Miya Woolfalk
Ph.D. Student
Harvard University
Government and Social Policy