Research by Right Media, the online ad exchange owned by Yahoo!, has found that in March 2007 59% of its global Exchange impressions were leaderboards, but this declined progressively over each three month interval and by December 2007 had dropped to 36.9%.  During the same period the number of medium rectangles traded worldwide increased strongly from 11.1% in March 2007 to 18.7% in December 2007.