Measuring Price Impact and Information Content of Trades in a Time-Varying Setting

The estimation of market impact is crucial for measuring the information content of trades and for transaction cost analysis. Hasbrouck's (1991) seminal paper proposed a Structural-VAR (S-VAR) to jointly model mid-quote changes and trade signs. Recent literature has highlighted some pitfalls of this approach: S-VAR models can be misspecified when the impact function has a non-linear relationship with the trade sign, and they lack parsimony when they are designed to capture the long memory of the order flow. Finally, the instantaneous impact of a trade is constant, while market liquidity highly fluctuates in time. This paper fixes these limitations by extending Hasbrouck's approach in several directions. We consider a nonlinear model where we use a parsimonious parametrization allowing to consider hundreds of past lags. Moreover we adopt an observation driven approach to model the time-varying impact parameter, which adapts to market information flow and can be easily estimated from market data. As a consequence of the non-linear specification of the dynamics, the trade information content is conditional both on the local level of liquidity, as modeled by the dynamic instantaneous impact coefficient, and on the state of the market. By analyzing NASDAQ data, we find that impact follows a clear intra-day pattern and quickly reacts to pre-scheduled announcements, such as those released by the FOMC. We show that this fact has relevant consequences for transaction cost analysis by deriving an expression for the permanent impact from the model parameters and connecting it with the standard regression procedure. Monte Carlo simulations and empirical analyses support the reliability of our approach, which exploits the complete information of tick-by-tick prices and trade signs without the need for aggregation on a macroscopic time scale