The nature of evidence synthesis

Evidence Live has come and gone and I had a wonderful chat with Iain Chalmers.  Iain is a marvel and in the course of the conversation I had a ‘light bulb’ moment relating to the nature of rapid versus systematic reviews.  I’m increasingly unhappy with the distinction and I am of the view that the debate should not be ‘rapid’ versus ‘systematic’ but how, for a given context, can we efficiently synthesise the available evidence.

For a given intervention you have a totality of evidence/data which has been generated in clinical trials.  This data is variably available:

The issue is when do we have enough data to be happy?  We will never get 100% of the evidence so we’re – in effect – using a sample.  Are we working with 10% of the evidence or is it 75% of the evidence?

Currently we typically rely on published journal articles.  This means we lack two important sources of evidence: unpublished studies and additional data from regulatory data and/or CSRs.  So, a systematic review based on published journal articles might synthesise 35% of the available evidence (my estimate, but it is based on the fact that 30-50% trials are unpublished and CSRs contain lots of additional evidence missed out in journal articles).

So, is this enough?  If it is, where’s the evidence that it’s enough?



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