Bloomberg lists a total of 457 US traded ETFs. We gathered the daily combined volume of all of these and compared it to the daily volume of the Russell 3,000 (which represents 98% of the investable US equity market).
The 20-day average of the ratio between the total US ETF volume and the Russell 3,000 volume has been steadily increasing, going from 0.135 last March to 0.254 currently. The correction last May saw a slight spike, but nothing like the spike we have seen in the past week. On February 27th (the day the S&P 500 was down 3.47%), the ratio of ETF volume to Russell 3,000 volume was 0.43. Remember, this is 457 ETFs versus 3,000 stocks.