Efficient markets models assert that the price of each asset is equal to the optimal forecast of its ex-post or fundamental value. These models do not imply, however, that the covariance between two asset prices is given by the covariance between the ex-post values they respectively forecast:...

We use high frequency data for the mark/dollar exchange rate for the period 1992-1995 to evaluate the effects of interventions. We estimate an unobserved components model that decomposes volatility into non-stationary and stationary parts. Stationary components in turn are decomposed into...