When I run the following code (fixed effect regression):
total_index_dem_model <- plm(SupDem ~ distance + gdpcap + pop + dem_duration + aut_neighbours ,data = df_a, index = c("country", "year"), model = "within", effect="twoways") summary(total_index_dem_model)
I get the following error:
0 (non-NA) cases In addition: Warning message: In pdata.frame(data, index) : duplicate couples (id-time) in resulting pdata.frame to find out which, use, e.g., table(index(your_pdataframe), useNA = "ifany")
I could not solve the problem. WHen I run the suggested code in the warning message nothing changes. Many thanks in advance.