Linders, G.J.M.

trade model poisson country gravity gravity model specification distance volume zero-inflated effect trade flows regression value log-normal estimation variable problem probability zippml zero-valued trade flows binomial trade patterns equation poisson model poisson regression model estimate poisson models nbpml gravity equation log-normal specification zero-inflated poisson model language zero-valued poisson specification barrier result paper log-normal model logarithmic transformation count zinbpml heckman selection model zero-valued flows overdispersion economic zero-inflated model research pattern alternative parameter statistic binomial regression model trade volume linder trade probability table tenreyro sample point analysis trade literature figure science account assumption silva trade barriers number variance likelihood agreement journal log-normal gravity equation trade agreement difference likelihood ratio test selection distribution error