dem.sub <- dem[dem[, "wbcode2"] <= 100, ]
dem.sub.panel <- PanelData(dem.sub, "wbcode2", "year", "dem", "y")
# create subset of data for simplicity
PM.results <- PanelMatch(lag = 4, refinement.method = "ps.match",
panel.data = dem.sub.panel, match.missing = TRUE,
covs.formula = ~ I(lag(tradewb, 1:4)) + I(lag(y, 1:4)),
size.match = 5, qoi = "att",
lead = 0:4, forbid.treatment.reversal = FALSE)
summary(extract(PM.results, qoi = "att"))
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