A reexamination of the market efficiency hypothesis: Evidence from an electronic intra-day, inter-dealer FX market

Researchers acknowledge that the evidence of autocorrelation (price dependency) in daily/weekly asset returns provides no conclusive evidence against the market efficiency hypothesis since the holding period of actual speculative positions may be less than a day. Using a high frequency (up to one hundredth of a second), transaction-based, electronic foreign exchange (FX) brokerage data set, we show that dealers in this market tend to close their speculative positions in less than a minute. We provide evidence that there is a significant negative autocorrelation in the rate of return on DM/USD exchange rate. However, when we sample data at frequencies shorter than a minute, profits are infeasible for two reasons: (1) the structure of the autocorrelation pattern is not consistent enough; (2) the largest potential speculative profit derived from the autocorrelation pattern is smaller than the regulated tick size. Our results support the market efficiency hypothesis as dealers have evidently engaged potentially profitable speculation based on price dependency.