When generating weights using nearest-neighbor matching with Mahalanobis distance, all of my weights for each treated and non-treated unit are "1". Below is my syntax using the MatchIt
package in R:
m_matched <- matchit(pko ~ lnatres + lgdppc + lpop + lmilper,
data = merged,
method = "nearest",
estimand = "ATT",
distance = "mahalanobis")
m_matched <- match.data(m_matched)
> summary(m_matched$weights)
# Min. 1st Qu. Median Mean 3rd Qu. Max.
# 1 1 1 1 1 1
I am not sure why this is the case and I am wondering if anyone has any idea of what error on my part may be causing this. Or is this somehow a part of this method of matching?