The evidence will eventually come from outcome studies done by well-trained and properly financed epidemiologists and health service researchers. Few of these people exist in the field of dermatology. This is well evidenced by the dearth of clinical epidemiologist or health services researchers who are tenured academic faculty. While wet lab scientists have been funded by the National Institutes of Health, Bethesda, Md, with the exception of melanoma, little research money has gone to dermatologic epidemiological studies. Unfortunately, even supporters of epidemiological work often fail to understand the rigor required of good work.
Epidemiological studies are expensive, person intensive, and require well-trained personnel.
It is doubtful that a clinical dermatology office is set up to conduct a well-designed epidemiological study. It is hard for me to imagine that most primary care physicians have either the training or the experience to provide better care than dermatologists. However, my beliefs are not good enough to persuade insurance providers. Perhaps, someday we will really know who treats the skin the best. It will take time.