Xt denotes the export volume of the crop under consideration, Qt the productive
capacity of the crop industry and Wt the weather. Px
/Pf
denotes the crop producer price
relative to the food price, and Px
/ Pn the crop price relative to the non-agricultural price.
Yt is the trade weighted income of the county’s trading partners and Ut a stochastic error
term satisfying the normal classical regression assumptions