[wkyle]

This is a common anecdotal example of Simpson's Paradox. Even if work performance is positively correlated with college ranking, a subset of selected grads can have a negative relationship with the same variables.

The mechanism is the selection criteria. Presumably, college ranking and demonstrated aptitude are both metrics used for hiring. Thus, if the variables are evaluated additively, and the examined firm occupies a single tier of the ranking+aptitude space, the hired employees will have a ranking/aptitude that falls along a negatively sloping line, similar to a budget constraint.

https://en.wikipedia.org/wiki/Simpson's_paradox