Since there's been a lot of talk recently about how light volume has been on US exchanges, I was doing a little research into historical volume trends. At the NYSE's website I found a data series which was one of the more interesting datapoints I've seen in a long time. It's a long term time series of turnover on the NYSE. Turnover is defined as number of shares traded per year divided by total number of shares listed. Turnover has fallen significantly in the last several years from a peak of 138% per year in 2008 to 73% per year currently. This turnover is up significantly from the mid 20th century when turnover rates were consistently in the low teens. But interestingly, turnover was at its highest at the beginning of the 20th century, when high frequency trading wasn't even conceivable.