We study the profitability of traders in two fully electronic and highly liquid markets: the Dow and Standard & Poor׳s 500 e-mini futures markets. Using unique information that identify counterparties to a transaction, we show and seek to explain the fact that the network pattern of trades captures the relations between behavior in the market and returns. Our approach includes a simple representation of how much a shock is amplified by the network and how widely it is transmitted. This representation provides a possible shorthand for understanding the consequences of a fat-finger trade, a withdrawing of liquidity, or other market shock.

We model the strategic provision of advice in environments where a principal's optimal action depends on an unobserved, binary state of interest. Experts receive signals about the state and each recommends an action. The principal and all experts dislike making errors in their decision and recommendations, respectively, but may have different costs of different errors. Is it in the principal's interest to let experts share information? Although sharing improves experts' ability to avoid errors, we identify a simple environment in which any principal, regardless of how he trades off the different errors, is worse off if he permits information sharing.