Support for `panelr::asym()`

[strengejacke]

trafficstars

library(panelr)

data("teen_poverty")
teen <- long_panel(teen_poverty, begin = 1, end = 5)
model <- asym(hours ~ lag(pov) + spouse, data = teen, use.wave=T)

summary(model)
class(model)

[IndrajeetPatil]

cc @jacob-long