Originally Posted by Kapusta

Earning a PhD implies that you (under the guidance of a mentor) have shown expertise in the very specific field/topic in which you did research. Along with the topical knowledge of that very specific field is an understanding of the accepted scientific research models and types of data/experiments/observations and expectations of that field, and also the accepted methods of analyzing that information (again, in that field).

Having a PhD in geology makes one an expert in bicycle tire research about as much as earning MD in orthopedics makes one able to diagnose heart problems. Sure, they will likely understand better than the average Joe, but it is not their area of expertise.

Further, getting a PhD is just the first step. It is what you do AFTER that which determines if you are an expert in your field. Or have much credibility as a scientist at all.