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Pre-post effect sizes should be avoided in meta-analyses.

P Cuijpers1, E Weitz1, I A Cristea2

  • 1Department of Clinical, Neuro and Developmental Psychology,Vrije Universiteit Amsterdam,The Netherlands.

Epidemiology and Psychiatric Sciences
|October 30, 2016
PubMed
Summary
This summary is machine-generated.

Pre-post standardized mean differences (SMDs) in meta-analyses can lead to biased outcomes and should be avoided. Between-group SMDs are a more reliable measure of treatment effects.

Keywords:
Individual patient datameta-analysespre-post effect sizesstandardised mean difference

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Area of Science:

  • Biostatistics
  • Psychological research methodology

Background:

  • Standardized mean difference (SMD) is a common effect size in meta-analyses.
  • Pre-post SMDs measure within-group changes, while between-group SMDs compare treatment to control groups.

Purpose of the Study:

  • To argue against the use of pre-post SMDs in meta-analyses.
  • To explain the reasons why pre-post SMDs can yield biased results.

Main Methods:

  • Analysis of arguments against pre-post SMDs.
  • Utilized individual patient data from a meta-analysis comparing cognitive behavior therapy and anti-depressive medication.

Main Results:

  • Pre-post SMDs are biased because baseline and post-test scores are not independent, and correlation is often unknown.
  • Pre-post SMDs are influenced by natural patient/setting variations, confounding intervention effects.
  • Between-group SMDs are superior as they control for these confounding variables.

Conclusions:

  • Pre-post SMDs should be avoided in meta-analyses due to probable outcome bias.
  • Between-group SMDs offer a more accurate and reliable estimation of treatment effects.