Recently gravity trade models are applied to disaggregated trade data. Here manyzeros are characteristic. In the presence of excess zeros usual Poisson Pseudo MaximumLikelihood (PPML) is still consistent, the variance covariance matrix howeveris invalid. Correct economic interpretation however...

Using estimation of demand for the George Washington/Jefferson NationalForest as a case study, it is shown that in a stratified/clustered on-sitesample, latent heterogeneity needs to be accounted for twice: first to accountfor dispersion in the data caused by unobservability of the process that...