ウェブ4.2 Conditional Distributions and Independence. Definition 4.2.1 Let (X, Y ) be a discrete bivariate random vector with joint pmf f(x, y) and marginal pmfs fX(x) and fY (y). For any x such that P (X = x) = fX(x) > 0, the conditional pmf of Y given that X = x is the function of y denoted by f(y|x) and defined by. f(x, y)