Why is class rank more important than GPA when applying for competitive residencies?

For example, a 3.7 at one school may put you at a much higher rank than a 3.7 at another school. And since we aren't graded on a curve, why would class rank be more indicative of a competent applicant than GPA?

Source: Student Doctor Network - October 31, 2017 Category: Universities & Medical Training Authors: Roy Williams Source Type: forums