For a simple reason, intra-day volatility is important not only to traders with very short holding periods, but to longer term investors as well: volatility in brief time intervals is a manifestation of the efficiency with which prices are set, and inefficient pricing can lead to unduly high execution costs for the short -run trader and the longer-run investor alike. While short period, intraday volatility has been observed to be high, the reason for its accentuation has not been adequately understood.