Meta-Analysis: An Introduction Bob O'Hara
Useful References Harrison, F. (2011) Getting started with meta-analysis.  Methods in Ecology and Evolution   2 : 1–10 htt...
The Problem: lots of studies of the same thing
We want to combine the studies “ Evidence synthesis”
Meta-analyses let us do this
“Meta-analysis” introduced in 1976 Glass, G.V. (1976) Primary, Secondary, and Meta-Analysis  of Research.  Educational Res...
...but the idea is much older Simpson, R.J.S. & Pearson, K. (1904)  Report On Certain Enteric Fever Inoculation Statistics...
Popular in Education and Medicine
...and now being used in biology <ul>Number of applied meta-analysis articles in ISI journals in Ecology and Evolution </u...
What It Does <ul><li>Combines studies' estimates of an effect </li><ul><li>e.g. the effect of a drug, from several clinica...
How to do it In 3 ½  steps
Step 1: Get your data <ul><li>Search the literature
Use criteria for deciding which studies should be included </li><ul><li>Must be clear here: want to avoid bias </li></ul><...
Step 2: Chose a statistic <ul><li>Effect size
Have to interpret on the same scale
Standardised </li><ul><li>Cohen's  d , Hedges'  g , Odds ratio, etc </li></ul></ul>
Step 3: Calculate & present the stats  <ul><li>Forest Plots </li></ul>
Step 3a: Publication bias? <ul><li>Funnel Plots </li></ul>“ File drawer problem”
Heterogeneity Across Studies <ul><li>Studies often measure slightly different things </li><ul><li>Same statistic, differen...
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Meta analyses

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Meta analyses

  1. 1. Meta-Analysis: An Introduction Bob O'Hara
  2. 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. 3. The Problem: lots of studies of the same thing
  4. 4. We want to combine the studies “ Evidence synthesis”
  5. 5. Meta-analyses let us do this
  6. 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. 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. 8. Popular in Education and Medicine
  9. 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. 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. 11. How to do it In 3 ½ steps
  12. 12. Step 1: Get your data <ul><li>Search the literature
  13. 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. 14. Step 2: Chose a statistic <ul><li>Effect size
  15. 15. Have to interpret on the same scale
  16. 16. Standardised </li><ul><li>Cohen's d , Hedges' g , Odds ratio, etc </li></ul></ul>
  17. 17. Step 3: Calculate & present the stats <ul><li>Forest Plots </li></ul>
  18. 18. Step 3a: Publication bias? <ul><li>Funnel Plots </li></ul>“ File drawer problem”
  19. 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. 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. 21. Finally: write it up
  22. 22. Finally: write it up ...and hide it in your bottom drawer

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