Meta-analysis

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==Where should I start?==
==Where should I start?==
*If you want to learn what is a meta-analysis...
*If you want to learn what is a meta-analysis...
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:#For the basics behind learning about meta-analyses
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:#For more in-depth
 +
:#
*If you want to start conducting a meta-analysis...
*If you want to start conducting a meta-analysis...
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+
:#For the basics
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:#
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:#
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===Three Basic Questions===
===Three Basic Questions===
A meta-analysis answers three general questions:
A meta-analysis answers three general questions:
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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?
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# 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.
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# 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.
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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?
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# 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===
===Five Basic Steps===
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==How do I conduct a meta-analysis?
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==How do I conduct a meta-analysis?==
===First, choose what statistical approach suits your needs===
===First, choose what statistical approach suits your needs===
===Second, choose which effect size to calculate?===
===Second, choose which effect size to calculate?===

Revision as of 00:31, 18 July 2006

Meta-analysis



Contents

Where should I start?

  1. For the basics behind learning about meta-analyses
  2. For more in-depth
  1. For the basics


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

Define your hypothesis Locate the Literature Identify and input data Cacluate Effect Sizes Analyze Variables


How do I conduct a meta-analysis?

First, choose what statistical approach suits your needs

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...

  1. There are generally three different statistical approaches to conduct a meta-analysis so first you need to choose which approach best fits your needs.

Hedges & Olkin Approach – Hedges, 1981; Hedges, 1982; Hedges & Olkin, 1985

Rosenthal & Rubin Approach – Rosenthal, 1991; Rosenthal & Rubin, 1978; Rosenthal & Rubin, 1988

Hunter, Schmidt, & - Hunter, Jackson, 1982; Hunter & Schmidt, 1990

File:Table1.gif

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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