As John mentioned, there are limits to short-term trading or portfolio composition data. However, there are a couple of relevant studies which feature intraday data that I transcribed from this pretty old IMF white paper:
Christie and Huang (1995) studied returns of US stock equities, finding that (controlling for clustering of correlated assets) dispersion on daily and monthly returns is higher at times of large stock movements. However, it's a pretty weak measure of "herding" because it's asset-specific, and overlooks assets of the same individual class/geographical region.
Kodres and Pritsker (1996) analysed public disclosures of intraday commodities trading data from the CFTC (i.e. only large participants), ran correlations/probit to see how likely participants will make the same trades when others are doing the same.
These studies seem to be very vanilla reg methods. I feel that the amount of "herding" is so market-specific and limited by paucity of data that I wouldn't dare generalise; I strongly suspect, however, that traders using technical analysis are implicitly trying to predict herding behaviors.