We formulate a measure of information efficiency in a general, no-arbitrage semimartingale model of the price process. The market quality measure is applied to a high-frequency dataset from the interdealer FX market to identify changes in market efficiency after a decimalization of tick size.

We study the relation between equity market uncertainty and the informational efficiency of U.S. equity prices, proxied by the SPDR S&P 500 Trust ETF. Using the Baker, Bloom, and Davis (2016) equity market uncertainty index, we document a negative relation between market uncertainty and...