From merrill lynch technical team:

Need 90% up day(s) as a sign of a bottom
We believe that before a low is in place we will need to get 90% upside days such
as we have seen in the major bottoms over the past two-years. Ninety percent
days generate strong buying or selling signals. Lowry’s Reports has been
studying supply/demand factors for decades. In 2002 Paul Desmond, president
of Lowry’s reports, wrote a paper, entitled “IDENTIFYING BEAR MARKET
BOTTOMS AND NEW BULL MARKETS,” which discussed the role of 90% up
days in identifying market bottom. He received the prestigious Charles H. Dow
Award from the Market Technicians Association. The definition for 90% up days is
points gained divided by the sum of points gained and points lost along with up
volume divided by the sum of up and down volume. Both ratios have to be in
excess of 90% to qualify. In order to create the chart below, we used NYSE
common stock breadth and NYSE composite upside and downside volume data.