A lot of it is, but you'd be surprised how many things clinicians do where there is no data, nor could we compile data because of ethical issues. For example, we do not know what is the optimal timing for providing patients with epinephrine when they are in cardiac arrest. We give 1mg every 3-5 minutes but there is NO data whatsoever stating that the interval and dose is appropriate. That being said, my practice is as evidence based as it could possibly be.
RE: Evidence-based medicine