Expectations of the maximum of sums and the sum of maxima for correlated normal variables

This paper compares expectations of the maximum of sums and the sum of maxima for correlated normal variables. General formulas are given for the expected differences and relative expected differences. Numerical values are computed for the special case of a correlated structure with common variance and covariance to illustrate the general magnitude of the differences which may occur. It is numerically shown that an approximation to the relative differences based on the extreme value distribution is very good. General correlated models with location-scale parameters are also considered. This result should be useful in application. Examples are discussed.