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?