has rio hit the bottom yet?, page-4

Goldman Sachs research shows that buy/sell spreads on ‘banned’ stocks in the US increased by 27 per cent relative to non-banned stocks on the first day of the ban – September 19 – and remained higher until the ban was lifted on October 9. The gap peaked in early October at 50 per cent, prior to the ban being lifted.

The Goldman Sachs research note says: “Causality is always extremely hard to prove … however (the figures) strongly suggest that the short-sell ban led to wider spreads. The implication is that at least some short-sellers provide useful liquidity to the market and help narrow spreads.