Chalk one up for Wall Street analysts.
The group known for being overly-bullish lemmings, got bearish in the last month ahead of the crack in the markets this week.
On average, about 4.5 percent of newly issued ratings for S&P 500 companies in the last year were sells, but in the last month that bumped up to a little over 5 percent, according to a CNBC analysis of the thousands of ratings in FactSet's broker database.
Sell and underweight ratings are very rare -- the vast majority of ratings for companies in the S&P 500 at any given time are buys or holds. In any given 30-day period, only a few hundred sell ratings are issued out of thousands of broker ratings. That means that it only takes a few dozen additional sells to move the needle substantially.
The half a percentage point movement in negative ratings we've seen in the last month is a relative change in sells of about 16 percent overall. That could be a temporary blip that disappears next month or the start of a wave of negative equity sentiment.