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Quality improvement research: are randomised trials necessary?
  1. D Neuhauser,
  2. M Diaz
  1. Epidemiology & Biostatistics, Medical School, Case Western University, Cleveland, Ohio, USA
  1. Correspondence to:
 Professor D Neuhauser
 Epidemiology & Biostatistics, Medical School, Case Weatern University, 1900 Euclid Avenue, Cleveland, Ohio, USA; dvn{at}

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Have you ever heard the criticism that a quality improvement project was not scientific because it was not carried out as a randomised controlled trial (RCT)? These critics have got it wrong and here is why. This answer requires a review of the scientific method. (There are lots of good references to the scientific method. See on “the scientific method”.)

At its core, science is based on generalisable theory. This theory leads to hypotheses which can be tested experimentally over and over again. If the test fails, the theory must be rejected or modified. Replication, not peer review, is the standard of scientific evidence.

Look at the pen in your hand. There is scientific theory called gravity from which you can hypothesise that if you let go of your pen it will fall to your desk top. Drop your pen and you have tested this hypothesis and supported the theory of gravity.

If instead, your pen flies into the air you may have thrown it, be on a space ship or in Harry Potter’s magic arts class. The first two possibilities are well defined and predictable by the full mathematical theory of gravity. The third possibility puts us in the realm of imagination which we can enjoy, but not replicate in reality. In a way, Harry Potter’s Hogwarts School is like pure mathematics. Both are built on assumptions that lead logically to imaginary behaviour or theory which are beyond our real world of experimentation.

Scientific theory simplifies reality, tells us what is important, and allows us to generalise to other circumstances. It does not matter for the simple theory of gravity whether your pen is blue or black or even if it is a pencil or a penny. Theory defines what is not relevant, and what is relevant (height …

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