A common multivariate distribution is the multivariate normal distribution, which is a
'combination' of a number of univariate normal random variables. It is important to note that when each individual random variable is normally distributed, the multivariate distribution that comprises these individual random variables is normal as well.

The z-value corresponding to the proportion 0.9000 is 1.28. We need to use the formula x = u + z o, where z = 1.28 to get the correct answer, or x = 516 + 1.28 x 20 = 541.6.

Haugen concluded that the market overreacts - with a lag and that "we apparently have a market that is slow to overreact."