Covriance

Why does covraince increase as the number of holdings increases?

I’m not sure what you mean.

Covariance is a measure of the interaction of _ two _ variables. No more, and no fewer.

If you can add some context I may be able to shed some light on it.

A small side note: I know it’s not in the CFA curriculum, but the term “interaction” has a very specific and a very different meaning in statistics than most people would think (check out the term in multiple linear regression). I would just refer to it (covariance) as measurement of the linear relationship between two variables.

Good point.

I was using it in a nontechnical sense.