Secrecy of Bank of Japan’s Yen Intervention: Evidence of Efficacy from Intra-daily Data

This chapter examines the intraday effectiveness of the Bank of Japan (BOJ)’s foreign exchange interventions over the period May 13 1991 to Mar 16 2004. The existing literature has generally failed to provide a comprehensive study on the effects of the BOJ’s interventions, and particularly, the efficacy of public and secret operations. By dividing a 24-hour trading day into three horizons, we show that the intraday evidence on the effects of official interventions documented in prior studies primarily came from publicly known interventions. In the case of secret interventions, although there were no clear impacts on the first moment of exchange rate returns, we found significant second moment responses. Specifically, covert operations were able to reduce the Yen/USD return volatility during both Tokyo and subsequent overnight market hours. Furthermore, our extended model on secret interventions reveals that when the BOJ completely concealed its transactions, undetected interventions were shown to be most effective in both reversing undesired trends and reducing excess return volatilities. On the other hand, those interventions that were rumoured were not as effective. Finally, the interventions conducted during the periods of ‘oral interventions’ were in general more effective in moving the exchange rate in the desired direction.