A paper I'm reading contains an equation with the following component:
$ w{}'\Sigma _{XX}w$
I've been told that this element is meant to reflect covariances among individuals.
w stands for weight. There are 428 individuals weighted equally. Therefore, each has a weight of 1/428 (0.0002).
I also have worked out the unique covariance between each pair of individuals. There are n choose k covariances, or 91378 in total. So I have a vector of 91378 covariances.
I am seeking to work out what the element resolves to. How do I use the information I have to work out $ w{}'\Sigma _{XX}w$? Is it just the average covariance?