Is there less informed trading after regulation fair disclosure?

I provide new tests of regulatory impact on informed trading in the stock market. After the implementation of Reg FD there is a significant decrease in the Hasbrouck [Hasbrouck, J., 1991a. The summary informativeness of stock trades: an econometric analysis. Review of Financial Studies 4, 571-595.] summary informativeness statistic, a measure of informed trading based on intra-daily trade level data. But, the switch to decimalization on the New York Stock Exchange has a much larger impact on this measure. These results highlight the difficulty in attributing specific effects to broad based regulatory events.