The historical practice of medicine has evolved over centuries based on empirical knowledge derived from experience and observation rather than rigorous scientific data. Over the second half of the twentieth century, this form of medical knowledge progress was largely supplanted by rigorous scientific data collection, particularly in the realm of cardiovascular diseases, where virtually every new drug discovery has been thoroughly evaluated in randomized clinical trials (RCT). The impressive improvement in the quality of the information provided by such study design has led to the development of an entirely new field in the medical knowledge which became known as Evidence-Based Medicine (EBM).

EBM soughs to move away from empirical information by providing a structured grading of the epistemological strength of evidence available. It further requires the highest levels of evidence to give strong recommendations for or against the use of any particular therapy. By this approach, RCTs are considered among the highest quality study designs which support those stronger recommendations. Still, despite their capability to avoid confounding and other biases, RCTs conclusions can only be interpreted as an overall averaged benefit for the collective population included in the study. Although such information may suffice to document the effect of any given therapy at the population level, this does not necessarily apply to any individual patient. While some individuals may benefit considerably more than the average population included in the study, other might benefit significantly less, whereas no benefit or even significant harm may occur in some individuals.

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