## Controlling Error Correlations with two indicators and with the following two models:
## dx = + 0.0012 /x^2 and dy = + 0.0071 x^3
errorcorr(datap, 2, datap$logGDP, datap$EmanzV,
f <- function(Y=c()) rbind(0.0012/Y[1]^2, + 0.0071*Y[1]^3), c(11), c(14))
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