Positive dependence. Two random variables (X, Y ) with c.d.f.

F(x, y) are said to be positively quadrant dependent if F(x, y) ≥ F(x,∞)F(∞, y)

for all x, y.

14 For the case that (X, Y ) takes on the four pairs of values (0, 0), (0, 1),

(1, 0), (1, 1) with probabilities p00, p01, p10, p11, (X, Y ) are positively quadrant dependent if and only if the odds ratio ∆ = p01p10/p00p11 ≤ 1.