Trumping Incomplete Models on Financial SpeculationTaxes

An NYT article on changes in governance rules in the European Union (EU) referred to the United Kingdom's opposition to a financial speculation tax supported by other members of the EU. The article noted that the UK cited a study done by the European Commission that found such a tax could lower GDP by 1.76 percent.

It is worth noting that this projected drop in GDP was derived from a model was intended as a work in progress, not a well developed forecasting technique. This model did not...