Barro Data Description. Version of the Barro Growth Data used in Koenker and Machado(). This is a regression data set consisting of observations on determinants of cross country GDP growth rates. Koenker, R. and Machado, J. () Goodness of Fit and Related Inference for Quantile Regression. Journal of the American Statistical Association, 94, Goodness of Fit and Related Inference Processes for Quantile Regression Roger KOENKER and Jose A. F. MACHADO Weintroduce a goodness-of-fit process for quantile regression analogous to the conventionalR2 statistic of least squares regression. Several related inference processes designed to test composite hypotheses about the combined effect of several covariates over.