The conceptual link between short sales and investor buying activity—the key to understanding what "short volume" really means—has never been clearly drawn before [now].

Whenever a market-maker fills an investor's buy order, the MM is facilitating the trade by shorting shares.

If you submit an order to buy 100 shares of XYZ at the market, you will buy those shares from an HFT.

Trades marked with the seller "short" comprise about 49% of equity share volume [ ... ] it's no coincidence.

The Dark Index™ (DIX™) has chronicled, in dollar-weighted terms, dark pool short volume across all components of the S&P 500® since 2011.

Very high relative percentages (≥45%) of dollar-weighted short volume are associated with mean 60-market-day returns of 5.3%, as compared to a mean of 2.8% across the whole dataset.

High levels of short volume correspond to positive medium-to-long term investor outlooks.

The SEC worries that providing too much data to the public may facilitate strategies disruptive to liquidity providers.