Hilariously, they are trying to make out that they've done something more clever than simply dividing trade deficit by exports, by posting an equation with additional parameters that are supposed to reflect the impact of price changes on imports and exports. Notwithstanding that this would vary massively from country to country (Lesotho - diamonds, Honduras, cheap textiles etc..) and notwithstanding that they have also omitted the value of service exports... the parameters make zero difference