Meta-analysis

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Meta-analysis

have you ever wanted to learn about meta-analysis or conduct a meta-analysis but didnt know where to start? This webpage is devoted to providing


Contents

Where should I start?

  1. For the basics behind meta-analyses see
  2. For more in-depth
  1. For the basics behind conducting a meta-analysis, see
  2. For more in-depth


What is a meta-analysis?

Definition

Three Basic Questions

A meta-analysis answers three general questions:
  1. Central tendency – The central purpose of a meta-analysis is to test the relationship between two variables such that X causes Y. Central tendency refers to identifying whether X affects Y via statistically summarizing signficance levels, effect sizes, and/or confidence intervals. You are trying to answer whether X affects Y, is the effect significant, and how strong is that effect?
  2. Variability – There is always going to be some degree of variation between the outcomes of the individual studies that compose the meta-analysis. The question is whether the degree of variablity is signficantly different than what we would expect by chance alone. If so, then its called heterogeneity.
  3. Prediction – If there is heterogeneity (variablitiy), then we look for moderating variables that explain the variablitty? In other words, does the effect of X on Y differ with moderator variables?

Five Basic Steps

There are generally five separate steps in conducting a meta-analysis:
  1. Define your hypothesis
  2. Locate the Literature
  3. Identify and input data
  4. Cacluate Effect Sizes
  5. Analyze Variables


How do I conduct a meta-analysis?

First, choose what statistical approach suits your needs

There are generally three different statistical approaches to conduct a meta-analysis so first you need to choose which approach best fits your needs. For an excellent detailed comparison of these three approaches, see (Johnson, Mullen, & Salas, 1995) (Comparison of Three Major Meta-Analytic Approaches. Journal of Applied Psychology, 80, 94-106). Some basic information from that article is posted below to get you started:
  1. Hedges & Olkin Approach(Hedges, 1981); (Hedges, 1982); (Hedges & Olkin, 1985)
  2. Rosenthal & Rubin Approach(Rosenthal, 1991); (Rosenthal & Rubin, 1978); (Rosenthal & Rubin, 1988)
  3. Hunter, Schmidt, & Jackson - (Hunter, Schmidt, & Jackson, 1982); (Hunter & Schmidt, 1990)
File:Table1.gif

Second, choose which effect size to calculate?

Third, choose your variables

If you want to follow the Hedges & Olkin approach...

If you want to follow the Rosenthal & Rubin approach...

If you want to follow the Hunter, Schmidt, & Jackson approach...

Just as an individual study collects data from many individuals (data points) that is statistically summarized to answer the question of interest, a meta-anlay












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