The regulatory debate concerning high-frequency trading (HFT) emphasizes the importance of distinguishing different HFT strategies and their influence on market quality. Using data from NASDAQ-OMX Stockholm, we compare market-making HFTs to opportunistic HFTs. We find that market makers...

We study order aggressiveness of market-making high-frequency traders (MM-HFTs), opportunistic HFTs (Opp-HFTs), and non-HFTs. We find that MM-HFTs follow their own group's previous order submissions more than they follow other traders’ orders. Opp-HFTs and non-HFTs tend to split market orders...