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Meta analyses
Meta analyses
Meta analyses
Meta analyses
Meta analyses
Meta analyses
Meta analyses
Meta analyses
Meta analyses
Meta analyses
Meta analyses
Meta analyses
Meta analyses
Meta analyses
Meta analyses
Meta analyses
Meta analyses
Meta analyses
Meta analyses
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Meta analyses

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A research group talk about meta-analyses

A research group talk about meta-analyses

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  • 1. Meta-Analysis: An Introduction Bob O'Hara
  • 2. Useful References Harrison, F. (2011) Getting started with meta-analysis. Methods in Ecology and Evolution 2 : 1–10 http://dx.doi.org/10.1111/j.2041-210X.2010.00056.x Podcast: http://bdown.astream.com/mee/fharrison.mp3 Stewart, G. (2010) Meta-analyses in applied ecology. Biol. Letters 6 : 78-81 http://dx.doi.org/10.1111/10.1098/rsbl.2009.0546
  • 3. The Problem: lots of studies of the same thing
  • 4. We want to combine the studies “ Evidence synthesis”
  • 5. Meta-analyses let us do this
  • 6. “Meta-analysis” introduced in 1976 Glass, G.V. (1976) Primary, Secondary, and Meta-Analysis of Research. Educational Researcher 5 : 3-8. http://dx.doi.org/10.3102/0013189X005010003
  • 7. ...but the idea is much older Simpson, R.J.S. & Pearson, K. (1904) Report On Certain Enteric Fever Inoculation Statistics. The British Medical Journal 2 : 1243-1246 http://www.jstor.org/stable/20282622
  • 8. Popular in Education and Medicine
  • 9. ...and now being used in biology <ul>Number of applied meta-analysis articles in ISI journals in Ecology and Evolution </ul><ul>Stewart G Biol. Lett. 2010;6:78-81 </ul><ul>©2010 by The Royal Society </ul>
  • 10. What It Does <ul><li>Combines studies' estimates of an effect </li><ul><li>e.g. the effect of a drug, from several clinical trials </li></ul></ul>
  • 11. How to do it In 3 ½ steps
  • 12. Step 1: Get your data <ul><li>Search the literature
  • 13. Use criteria for deciding which studies should be included </li><ul><li>Must be clear here: want to avoid bias </li></ul></ul>
  • 14. Step 2: Chose a statistic <ul><li>Effect size
  • 15. Have to interpret on the same scale
  • 16. Standardised </li><ul><li>Cohen's d , Hedges' g , Odds ratio, etc </li></ul></ul>
  • 17. Step 3: Calculate & present the stats <ul><li>Forest Plots </li></ul>
  • 18. Step 3a: Publication bias? <ul><li>Funnel Plots </li></ul>“ File drawer problem”
  • 19. Heterogeneity Across Studies <ul><li>Studies often measure slightly different things </li><ul><li>Same statistic, different species </li></ul><li>Means extra variation </li><ul><li>Use random effects models </li></ul></ul>
  • 20. Meta-regressions <ul><li>Use properties of study to explain responses </li><ul><li>e.g. does body size affect the statistic? </li></ul><li>In essence a weighted regression </li></ul>Has potential to become very complicated
  • 21. Finally: write it up
  • 22. Finally: write it up ...and hide it in your bottom drawer

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