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Centre for Evidence-
Based Medicine

Are the results of this study valid?

Anytime we do a search, finding a systematic review should be our first goal. (Note: the critical appraisal of systematic reviews requires the skills for appraising individual studies and therefore you might want to review the section on critically appraising single therapy trials before tackling this one).

A systematic review is a summary of the medical literature that uses explicit methods to systematically search, critically appraise and synthesise the literature on a specific topic. Let's start by returning to our clinical scenario from the question formulation tutorial:

You admit a 75 year old man with a stroke (left sided weakness) who is having trouble ambulating, feeding, bathing and dressing himself. He has hypertension but it is well controlled with a diuretic. He is otherwise well and now that he is medically stable you decide after discussion with him to transfer him to a stroke unit. His family asks to see you because they are concerned about this transfer. They live very close to the acute care hospital and wonder why he can't stay on the general medical ward where he currently is. You arrange to meet with him and his family to discuss their concerns. In the meantime, you decide to review the evidence for the use of stroke units.

In the tutorial on clinical questions we formulated the following question: In an elderly man with a stroke, does admission to a stroke unit decrease the risk of death and dependency?

Our search of the literature to answer this question retrieved an article from the The Cochrane Library (Stroke Trialists' Collaboration. Cochrane Library, Update Software, 1999, Issue 4).

How can we critically appraise this paper? We'll start off by considering validity and the following list outlines the questions that we need to consider when deciding if a systematic review is valid.

  1. Is this a systematic review of randomised trials?
  2. Does it include a methods section that describes: a) finding and including all the relevant trials, and b) assessing their individual validity?
  3. Were the results consistent from study to study?

    A finer point:
  4. Were individual patient data (or aggregate data) used in the analysis?