I think another thing to factor in is the increase in computerized trading. With more and more volume comprising of strategies that focus on the short term, it

I think another thing to factor in is the increase in computerized trading. With more and more volume comprising of strategies that focus on the short term, it seems like the returns may not be as shown since the data the research is based on covers traditional trading periods. not just HFT, buy algo shops like PDT and Renaissance Technologies being more and more frequent players