Exchange traded funds (ETFs) that track a specified index are a financial technology that has risen dramatically in the last two decades. We model an ETF's optimal index replication strategy and show that it involves underweighting or omitting illiquid index assets. Instrumenting for ETF trading...

We analyze the contribution to price discovery of market and limit orders by high frequency traders (HFTs) and non-HFTs. While market orders have a larger individual price impact, limit orders are far more numerous. This results in price discovery occurring predominantly through limit orders....

We exploit an optional colocation upgrade at NASDAQ OMX Stockholm to assess how speed affects market liquidity. Liquidity improves for the overall market and even for noncolocated trading entities. We find that the upgrade is pursued mainly by participants who engage in market making. Those that...

We study performance and competition among high-frequency traders (HFTs). We construct measures of latency and find that differences in relative latency account for large differences in HFTs' trading performance. HFTs that improve their latency rank due to colocation upgrades see improved...

We examine the effects of high frequency traders (HFTs) on liquidity using the September 2008 short sale ban. To disentangle the separate impacts of short selling by HFTs and non-HFTs we use an instrumental variables approach exploiting differences in the ban's cross-sectional impact on HFTs and...