Positive association of two events
= Positive association of two events
{title2=$P(A\cap B)>P(A)P(B)$}
For nontrivial <events>, strict attraction under <conditional probability> is equivalent to a positive covariance of their indicator variables. This condition is symmetric in the two <events>. Complementing exactly one of the <events> reverses the strict inequality. This two-event condition should be distinguished from association of an entire family of random variables.