Meta-analysis

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Meta-analysis
Meta-analysis
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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
==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 the basics behind meta-analyses see
:#For more in-depth
:#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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:#For the basics behind conducting a meta-analysis, see
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:#
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:#For more in-depth
:#
:#
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===Definition===
===Definition===
===Three Basic Questions===
===Three Basic Questions===
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A meta-analysis answers three general questions:
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:A meta-analysis answers three general questions:
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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?
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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?
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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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#'''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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# 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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:There are generally five separate steps in conducting a meta-analysis:
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Define your hypothesis
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#'''Define your hypothesis'''
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Locate the Literature
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#'''Locate the Literature'''
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Identify and input data
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#'''Identify and input data'''
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Cacluate Effect Sizes
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#'''Cacluate Effect Sizes'''
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Analyze Variables
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#'''Analyze Variables'''
==How do I conduct a meta-analysis?==
==How do I conduct a meta-analysis?==
===First, choose what statistical approach suits your needs===
===First, choose what statistical approach suits your needs===
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: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:
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#'''Hedges & Olkin Approach''' – [[Hedges, 1981]]; [[Hedges, 1982]]; [[Hedges & Olkin, 1985]]
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#'''Rosenthal & Rubin Approach''' – [[Rosenthal, 1991]]; [[Rosenthal & Rubin, 1978]]; [[Rosenthal & Rubin, 1988]]
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#'''Hunter, Schmidt, & Jackson''' -  [[Hunter, Schmidt, & Jackson, 1982]]; [[Hunter & Schmidt, 1990]]
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::[[Image:Table1.gif]]
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===Second, choose which effect size to calculate?===
===Second, choose which effect size to calculate?===
===Third, choose your variables===
===Third, choose your variables===
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:#There are generally three different statistical approaches to conduct a meta-analysis so first you need to choose which approach best fits your needs.
 
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Hedges & Olkin Approach – Hedges, 1981; Hedges, 1982; Hedges & Olkin, 1985
 
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Rosenthal & Rubin Approach – Rosenthal, 1991; Rosenthal & Rubin, 1978; Rosenthal & Rubin, 1988
 
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Hunter, Schmidt, & - Hunter, Jackson, 1982; Hunter & Schmidt, 1990
 
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::[[Image: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
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

Revision as of 00:49, 18 July 2006

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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