Why Do Security Prices Change? A Transaction-Level Analysis of NYSE Stocks

This paper develops a structural model of intraday price formation that embodies both public information shocks and microstructure effects. Due to its structural nature, the model's underlying parameters provide summary measures to assess trading costs, the sources of short-run price volatility, and the speed of price discovery in an internally consistent, unified setting. We estimate the model using transaction level data for a cross-section of NYSE stocks. We find, for example, that the parameter estimates jointly explain the observed U-shaped pattern in quoted bid-ask spreads and in price volatility, the magnitude of transaction price volatility due to market frictions, and the autocorrelation patterns of transaction returns and quote revisions. Further, in contrast to bid- ask spread patterns, we find that execution costs of a trade are much smaller than the spread and increase monotonically over the course of the day. This may provide an explanation for why there is concentration in trade at the open