Hi there,
I'm wondering what Zelig in the following situation (code below) actually
does. Is this considered as a so called regression adjustment after the
propensity score matching?
library(MatchIt)
library(Zelig)
data(lalonde)
re78 represents the outcome variable
1. With Zelig
m.out <- matchit(treat ~ age + educ + black + hispan + married + nodegree +
re74 + re75, data = lalonde)
z.out <- zelig(re78 ~ distance, data = match.data(m.out,
"control"), model = "ls")
x.out <- setx(z.out, fn = NULL, data = match.data(m.out,
"treat"), cond = TRUE)
s.out <- sim(z.out, x = x.out)
summary(s.out)
2. Without Zelig - only matching
T.output <- match.data(m.out, group="treat")$re78
C.output <- match.data(m.out, group="control")$re78
ATT <- mean(T.output)-mean(C.output)
ATT
ATT between 1. and 2. is quite different.
Hope to hear some thoughts regarding this.
Many thanks!
Ana
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