I am occasionally asked why we promote clinical research so much within the discipline of family practice. My answer is that without clinical research we have no evidence of whether we are doing harm or good. A classic example of the need for clinical research is the relationship between smoking and cancer. Until Richard Doll undertook this research we had no idea of the risk of smoking. 
Richard Doll is one of the major role models for clinical epidemiology and clinical research. His multiple studies, and the presentation of his findings over a period of four years eventually led to the UK government to accept the link between smoking and lung cancer. Tomorrow would have been his 100th birthday and this is his BMJ obituary & classic paper on smoking & lung ca http://t.co/enwdc0iR & http://www.bmj.com/content/328/7455/1529.reprint
For video content http://www.bmj.com/multimedia/video/2009/05/21/man-who-stopped-smoking
Martin