A popular recommendation to programmers in object-oriented software is to "program to an interface, not an implementation" (PTI). Expected benefits include increased simplicity from abstraction, decreased dependency on implementations , and higher flexibility. Yet, interfaces must be immutable, excessive class hierarchies can be a form of complexity, and "speculative generality" is a known code smell. To advance the empirical knowledge of PTI, we conducted an empirical investigation that involves 126 Java projects on GitHub, aiming to measuring the decreased dependency benefits (in terms of cochange).