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Negative trials pp


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Negative trials pp

  1. 1. Negative trials in neurosurgery –What positives can we take from them? Neurosurgery debate 31 May 2012 Negative trials 1
  2. 2. Negative trials in neurosurgery• Dr Patel - SAMMPRIS (2011)• Dr Bervini - COSS (2011)• Dr Lai - IHAST (2005)• Dr Gragnaniello - Vertebroplasty (2009)• Dr Paramasvaran - INTERPHONE (2010)• Dr Liu - DECRA (2011) Negative trials 2
  3. 3. What is a negative study?• Inconclusive ‘no evidence of effect’ – Inadequately powered, poor methodology• Clear evidence of ‘no effect’ – Well designed, adequately powered• Clear evidence of harm – Sandercock, 2011 (Int J Stroke) Negative trials 3
  4. 4. Why a negative result?• Internal validity – Trial design – Study size (power effects) – Bias – Statistical analysis• External validity – Inclusion/exclusion criteria – Generalisability Negative trials 4
  5. 5. Why should a negative study be published?• Ethical – Participants’ contribution should be acknowledged• Scientific – Contribute to knowledge• Systematic reviews – Publication bias• Funding conditions Negative trials 5
  6. 6. What can we learn from a negative study?• Should the intervention be subjected to further studies?• Should the intervention continue in selected populations?• Should the intervention be abandoned? Negative trials 6
  7. 7. Presentations• 10 minutes presentation• 5 minutes questions• Assessment – Oral presentation – Use of visual material – Critical appraisal – internal validity – Critical appraisal – external validity – Response to questions Negative trials 7