68. If X and Y have a bivariate normal distribution with correlation coefficient p > 0, they are positively regression-dependent. [The conditional distribution of Y given x is normal with mean n + p'TO-1(x - 0 and variance 'T 2(1 - p2). Through addition to such a variable of the positive quantity p'TO-1(x' - x) it is transformed into one with the conditional distribution of Y given x' > x.]