a b y1 y2 y3 y4
-1 -1 18.2 18.9 12.9 14.4
 1 -1 27.2 24.0 22.4 22.5
-1  1 15.9 14.5 15.1 14.2
 1  1 41.0 43.9 36.3 39.9