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Flow Toxicity and Liquidity in a High-frequency World

Read the paperopens doi.org in a new tab

What they found

The authors introduced VPIN (volume-synchronized probability of informed trading), a real-time version of PIN that measures order imbalance over volume buckets rather than clock time. Using E-mini S&P 500 futures data around the May 6, 2010 flash crash, they showed that VPIN reached historically high levels in the hours before the crash, consistent with market makers facing increasingly toxic (informed) order flow and withdrawing liquidity. They proposed VPIN as an early-warning indicator of liquidity-driven volatility.

See it drawn

Original diagrams for the ideas on this page. Illustrative, not real market data.

Bid-ask spread in an order bookSell orders stacked above buy orders with a gap between the best of each.SELLERS (asks)50.0690050.051,40050.0460050.011,10050.002,30049.99800spread = 0.03BUYERS (bids)
The bid-ask spread. Buy orders sit below, sell orders above, and the gap between the best bid (50.01) and best ask (50.04) is the spread you pay to cross. Bar length shows the size resting at each price.

What you can use

  • Persistent one-sided order flow drives market makers away, and their withdrawal is what turns a sell-off into a crash.
  • Measuring time in volume rather than minutes matches how market makers experience risk.
  • When order flow becomes very lopsided, expect spreads to widen and slippage to spike; that is not the time to use market orders.

Caveats

VPIN's predictive power for the flash crash has been disputed (Andersen and Bondarenko argued it is mostly a volatility proxy). Derived from futures data; implementation details matter a lot.

Tags: microstructure, order-flow, vpin, flash-crash

Summaries are our own reading of the paper, not the authors' words. Educational only, not advice. Discuss it in Book Club.