 As we have seen in  Section 5,  hierarchies of evidence in evidence-based medicine rank study results from “systematic” clinical research such as RCTs and observational studies higher than “unsystematic” expert opinion. The epidemiologists who initiated the formal EBM movement in the early 1990s had good reason to be skeptical about expert opinion. When therapies are subjected to systematic tests, tradition and expert opinion are sometimes shown to be flawed. John Worrall discusses three examples: grommets for glue ear, ventricular ectopic beats repressing substances such as encainide or flecainide for cardiac arrest, and routine fetal heart rate monitoring to prevent infant death (Worrall 2007a: 985). In each case we have a procedure the effectiveness of which is indicated by common sense and knowledge about the patho-physiological pathways—glue ear is a condition produced by a build-up of fluid in the middle ear that is unable to drain away because of pressure differentials, grommets act by letting air into the middle ear and thereby equalizing pressure, for instance—but which, when tested by a randomized trial, turns out to be ineffective at best and positively harmful in the worst case.