What the Tick Test Can and Cannot Reveal About Trade Direction
Summary
The document asks why the tick test is used to infer whether trades are buyer or seller initiated. The rule labels a trade by comparing its price with the previous different trade price: an uptick suggests a buy, while a downtick suggests a sell. The discussion places this heuristic within short-horizon market microstructure, where trade direction is not always directly observed.
An answer explains that order-by-order depth-of-book data can identify the taking order as the initiating side. It also describes complications from iceberg orders and auctions, where the inferred direction may differ from a simple reading of the displayed trade. The example illustrates how several executions associated with an iceberg can be classified as seller initiated. The material does not provide empirical accuracy measurements for the tick test; one contributor questions its reliability and suggests comparing it with exchange-provided side labels. Thus, the tick test is presented as an inference shortcut, not a definitive account of aggressor side.
Key ideas
- The tick test infers trade direction from price changes relative to the previous different trade price.
- A price rise is treated as evidence of buyer initiation, and a price fall as evidence of seller initiation.
- Order-by-order data can identify the incoming order that executes against resting liquidity.
- Iceberg and auction executions can complicate trade-side interpretation.
- The document offers no accuracy results and suggests checking inferred sides against exchange labels when available.
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Full text
# Mechanism for Tick Rule for Trade Classification # Mechanism for Tick Rule for Trade Classification I see a few papers using the following tick test to classify a trade as buy/sell initiated trades: compare a trade price to the previous differing trade price, if the current price is higher/lower, then it is a buy/sell. This method is easy to implement but I do not understand the reason behind it: is there any fundamental mechanism that makes it more likely to be correct? ## Answer by Pleb (score 2, accepted) https://quant.stackexchange.com/a/60364 This is a quantifiable way to infer some understanding of the trade direction under very short time horizons (market microstructure). There exists a couple of other trade direction algorithms, which is neatly described in this paper. ## Answer by Sergei Rodionov (score 1) https://quant.stackexchange.com/a/60611 In an order-by-order depth-of-book feed, the trade direction is based on the taking order. If an incoming BUY order is immediately matched with a standing SELL order, the direction is BUY. Things get a bit more interesting with icebergs and auction orders, in which case the trade direction is typically opposite of the earliest of the two originating orders. Iceberg example: ``` time,num,price,quantity,direction .001,001,20.00,100,B (100 display of 300 iceberg order, 200 hidden) .002,002,15.00,300,S .002,003,15.00,100,B (100 display of 300 iceberg order, 100 hidden) .002,004,15.00,100,B (100 display of 300 iceberg order, 0 hidden) ``` The trade direction of all three trades above is SELL. I don't think comparing prices of consecutive trades is a meaningful indicator of direction. But I have the feed available where the direction (aka side) is classified by the exchange itself and I could run some tests on empirical data.
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