Here is a link to my 30th Quartz column “Speed Limit–How to avoid another Nasaq meltdown: Slow down trading.”

Let me mention one thing to watch out for if (to bolster the argument that high-frequency trading adds to liqiuidity) someone brings to the table empirical evidence on the effect of high-frequency trading bid/ask spreads: front running by the market makers can raise trading costs too. The extra trading costs from the front running of high-frequency trading should be added to the usual bid/ask spread; just because a trading cost is less visible than bid/ask spreads doesn’t mean it doesn’t count.