Ben Bernanke in his paper "The Macroeconomics of the Great Depression: A Comparative Approach" writes:

The broadening of focus [to include the study of other countries] is important [because] by effectively expanding the data set from one observation to twenty, thirty, or more, the shift to a comparative perspective substantially improves our ability to identify-in the strict econometric sense-the forces responsible for the world depression.

Discuss at least two reasons why one might worry about using cross-country evidence to identify the role played by the gold standard in the Depression. Concretely, consider using variation in when different countries left the gold standard to identify the effects of the gold standard.