What is evidence based medicine?
David Sackett and others describe evidence based medicine (EBM) in the following way:
Evidence based medicine is the conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients. The practice of evidence based medicine means integrating individual clinical expertise with the best available external clinical evidence from systematic research. 
Thus there are three issues to be considered:
The care of individual patients: This is the starting point for any medical science, because it is the problem which any system of medicine has to address. EBM recognises this as much as homeopathy does, but its approach to the issue differs from homeopathy because it has no way of objectively relating the individual’s symptoms to the necessary individual treatment. Instead it draws from two sources of information: individual clinical expertise and external evidence.
Individual clinical expertise: Traditionally the only source of information about treatment was either the previous experience of individual practitioners, passed on through word of mouth or publications, or experience gained by experimenting oneself. As such this information is based on the experience of treating individuals and of observing which of the available treatments is most successful. On the other hand this body of knowledge is dependent on the quality of the practitioners' records, including the trustworthiness of the practitioners in accurately reporting their experience. In addition, without objective criteria for determining the relationship of the effects of treatment to the symptoms being treated, any conclusions based on this information cannot be scientifically verified.
Evidence from systematic research: In an attempt to provide an objective basis for assessing the effectiveness of treatments, methods of research were developed, including the randomised controlled trial (RCT) and its more rigorous form the double-blind RCT (DBRCT). The assumption underlying the RCT and other methods of research based on it, is that any treatment which has a beneficial effect on a large number of people will be more likely to be beneficial in an individual case. In fact this assumption has not only not been scientifically verified, but the evidence indicates that it is not valid. As a result this evidence has to be qualified by the experience of skilled practitioners. As Sackett et al. put it:
Good doctors use both individual clinical expertise and the best available external evidence, and neither alone is enough. Without clinical expertise, practice risks becoming tyrannised by evidence, for even excellent external evidence may be inapplicable to or inappropriate for an individual patient. Without current best evidence, practice risks becoming rapidly out of date, to the detriment of patients. (1)
The RCT came to prominence in the latter half of the twentieth century in response to concerns about the quality of research into new drugs, especially as regards their safety, and RCTs are certainly an appropriate method for assessing a drug’s potential to cause harm. However, as a result of becoming a procedure central to testing the safety of orthodox drugs, the RCT has gradually come to be seen as the “gold standard” for measuring the effectiveness of drugs as part of EBM. Indeed some proponents of EBM go so far as to maintain that DBRCT is the only valid test of the effectiveness of a treatment, despite the fact that there is no scientific support for this position, and abundant evidence of its scientific inadequacy. It is important to note that within orthodox medicine itself there is concern at the degree of concentration on this method to the exclusion of other methods. [2,3,4]
A narrow focus on RCTs also ignores both the enormous quantity of recorded homeopathic cases (whether in original detailed notes or synopses) which constitute evidence of clinical expertise, and patient outcome studies which constitute evidence of effectiveness in individual care. Within the terms of EBM both these sources of information are valid and of significance to an assessment of effectiveness.
Lastly, it is important to bear in mind that demands for the use of the EBM approach arise in the first place from a circumstance peculiar to orthodox medicine in comparison with mature sciences, such as physics and chemistry. Where experiments in these latter sciences involve testing the predictive powers of a theory in order to develop a fuller understanding, in orthodox medicine there does not appear to be a robust theoretical framework that relates health, disease and treatment. As a result experiments to test drugs do not compare experience against predictions derived from an overarching theory, but compare bodies of evidence with each other.
Sackett et al., ‘Evidence based medicine/ what it is and what it isn't’, British Medical Journal, 312 (1996), 71-72 at http://www.bmj.com/cgi/content/full/312/7023/71, accessed 6 December 2008.
Dave Holmes, Stuart J Murray, Amélie Perron, “Deconstructing the evidence-based discourse in health sciences: truth, power and fascism” in Int J Evid Based Healthc 2006; 4: 180–186.
Andrew James Turner, Evidence Based Medicine, 'Placebos' and the Homeopathy Controversy (PhD thesis), University of Nottingham, 2012.
Trisha Greenhaugh, Jeremy Howick and Neal Maskrey, 'Evidence based medicine: a movement in crisis?, British Medical Journal, 348 (2014).
Why it works