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Publication/Availability Bias

Publication/Availability Bias. Problems with bad data. Problem of missing studies. Missing at random is okay Nonrandom is a problem Sources of nonrandom samples of studies Publication bias – significant, small N Grad student work; other filedrawer

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Publication/Availability Bias

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  1. Publication/Availability Bias Problems with bad data

  2. Problem of missing studies • Missing at random is okay • Nonrandom is a problem • Sources of nonrandom samples of studies • Publication bias – significant, small N • Grad student work; other filedrawer • Deliberate misrepresentation for financial reasons

  3. Forest Plot Drift to the right by precision? Source: Borenstein, Hedges, Higgins & Rothstein, 2009, p. 282

  4. Funnel plot Assymetry? Esp lower right. These appear biased and heterogeneous to me. Source: Sutton (2009). In Cooper, Hedges, & Valentine (Eds) Handbook fo Research Synthesis Methods p. 501

  5. Fail-safe N • How many studies do we need to make the result n.s.? (Rosenthal) • How many studies do we need to make the summary effect small enough to ignore? (Orwin) kfs = failsafe studies kobt = studies in meta dobt = summary ES dc = desired lower boutnd dfs= studies with this (eg 0) size needed to lower ES Corwin, R. G. (1983). A fail-safe N for effect size in meta-analysis. Journal of Educational Statistics, 8, 157-159.

  6. Trim & Fill Creates symmetry; Adjusts summary ES Source: Borenstein, Hedges, Higgins & Rothstein, 2009, p. 287

  7. Cumulative Forest Source: Borenstein, Hedges, Higgins & Rothstein, 2009, p. 288

  8. Egger’s Regression Ti = effect size; vi=sampling variance of ES Should be flat (centered) if no bias. This shows small studies have higher values. Source: Sutton (2009). In Cooper, Hedges, & Valentine (Eds) Handbook fo Research Synthesis Methods p. 441

  9. Sensitivity Analysis Outliers. Run twice. Pray. Source: Greenhouse & Iyengar (2009). In Cooper, Hedges, & Valentine (Eds) Handbook fo Research Synthesis Methods p. 422

  10. Sensitivity Analysis Varying levels of tau-squared Source: Louis & Zelterman (1994). In Cooper, Hedges (Eds) Handbook of Research Synthesis p. 418

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