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Price Impact: Nonlinear, Temporary Effects of Order Flow

Article arXiv papers · Author: J. P. Bouchaud
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Summary

The document introduces price impact, explains how it is measured and modelled in recent research, and questions the intuitive idea that trades move prices through a simple, direct mechanism. It highlights empirical evidence that signed order flow and price changes are strongly correlated, while emphasizing that this relationship does not imply a linear response to trade volume or a lasting price effect.

The discussion links price impact to information: trading can help incorporate private information into market prices. At the same time, order flow also contains random fluctuations, which can contribute to market volatility even when trades convey no useful signal. This framing matters for execution and market microstructure because measured impact may combine informational effects with noise. The summary provides qualitative conclusions rather than a specific estimation method, dataset, or numerical evidence, and it does not prescribe a trading strategy. Its main caveat is that price impact is more complex than a single permanent force proportional to volume.

Key ideas

  • Signed order flow is strongly correlated with price changes in empirical studies.
  • The price response to trading volume is not necessarily linear.
  • Trade impact is not necessarily permanent.
  • Order flow can convey private information that becomes reflected in prices.
  • Random variation in order flow can also contribute to market volatility.

Tags

Market microstructureExecutionStatisticsVolatility
Full text
# Price Impact


# Price Impact









We define what "Price Impact" means, and how it is measured and modelled in the recent literature. Although this notion seems to convey the idea of a forceful and intuitive mechanism, we discuss why things might not be that simple. Empirical studies show that while the correlation between signed order flow and price changes is strong, the impact of trades on prices is neither linear in volume nor permanent. Impact allows private information to be reflected in prices, but by the same token, random fluctuations in order flow must also contribute to the volatility of markets.

Shown in full with attribution under the source's licence. Licence: abstract CC0

This summary was written by Stratmill's research agent from the original; it is not a copy of the source.