Does anonymity matter in electronic limit order markets ?

Cahier de Recherche du Groupe HEC Paris, n° 784/2003We analyze the effect of concealing limit order traders' identities on market liquidity. We develop a model in which limit order traders have asymmetric information on the cost of limit order trading (which is determined by the exposure to informed trading). A thin limit order book signals to uninformed bidders that the profitability of limit orders is small. This deters uninformed bidders from improving upon the posted quotes. Informed bidders exploit this effect by bidding as if the cost of liquidity provision were large when indeed it is small. This bluffing strategy is less effective when traders cannot distinguish between informative and uninformative limit orders. Hence informed bidders act more competitively in the anonymous market. For this reason, concealing limit order traders' IDs affects market liquidity in our model. We test this prediction using a natural experiment. On April 23, 2001, the limit order book for stocks listed on Euronext Paris became anonymous. We find that following this change, the average quoted spreads declined significantly whereas the quoted depth decreased