Meta-analysis

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===Five Basic Steps===
===Five Basic Steps===
:There are generally five separate steps in conducting a meta-analysis:
:There are generally five separate steps in conducting a meta-analysis:
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#<u>Define your hypothesis</u> – From readhing literature, define, set boundaries, etc.
+
#<u>Define your hypothesis</u> – First you must have a well-defined statement of the relationship between the variables under investigation so that you can carefully define the inclusion and exclusion criteria when locating potential studies. Chapter 2 of
 +
 
 +
From readhing literature, define, set boundaries, etc.
#<u>Locate the Literature</u> – The central
#<u>Locate the Literature</u> – The central
#<u>Identify and input data</u> – Gather empiricial findings from primary studies (e.g., p-value, effect size, etc) and input into statistical database.
#<u>Identify and input data</u> – Gather empiricial findings from primary studies (e.g., p-value, effect size, etc) and input into statistical database.
#<u>Cacluate Effect Sizes</u> – Calculate the overall effect -- effect size, significance level or confidence intervals associated with the effect size, and variaiblity (homogeneity) of the effect.
#<u>Cacluate Effect Sizes</u> – Calculate the overall effect -- effect size, significance level or confidence intervals associated with the effect size, and variaiblity (homogeneity) of the effect.
#<u>Analyze Variables</u> – Code your study variables, input the data into the database, and analyze the results. There are two types of study variables: (a) objective variables -- such as type of IV or DV, ..., (b) subjective variables -- inferential judgements made by two or more judges....
#<u>Analyze Variables</u> – Code your study variables, input the data into the database, and analyze the results. There are two types of study variables: (a) objective variables -- such as type of IV or DV, ..., (b) subjective variables -- inferential judgements made by two or more judges....
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==How do I conduct a meta-analysis?==
==How do I conduct a meta-analysis?==

Revision as of 03:53, 21 July 2006

► Have you ever wanted to learn about meta-analysis or conduct a meta-analysis but didn't know where to start? This webpage is devoted to providing you expert opinion on what you need to know to start your own meta-analysis.

► With the thousands of meta-analyses conducted in all areas of psychology over the past few decades, there has been an ever-increasing number of articles, books, and software programs devoted to how to conduct meta-analyses. Below, experts on meta-analysis provide their suggesstions on which which of the many sources of information are the most useful and why -- so that the user has an easy-to-use starting place for learning everything about meta-analyses.



Contents



Where should I start?

If you want to learn what is a meta-analysis...

  1. For the basics, see below where we lay out:

  2. For more in-depth discussion and explanations, we recommend...
    • start first with (Johnson & Eagly, 2000) which is a chapter from the "Handbook of Research Methods in Social and Personality Psychology" that provides an excellent detailed explanation of each stage in the meta-analysis process including the advantages of meta-analysis compared to traditional literature reviews, statistical forumlas for analyzing effect sizes from various indexes and study designs, and discussion of how to visually depict your data.
    • then for even more in-depth descriptions see (Cooper & Hedges, 1994) (Handbook of Research Synthesis) which provides a separate chapter on every step involved in designing, analyzing, and writing-up a meta-analysis.

If you want to learn how to start conducting a meta...

  1. For the basics, see below were we lay out:

  2. For more in-depth discussion and explanations, we recommend...
    • start first with (Johnson, Mullen, & Salas, 1995) which provides a statistical comparision of the three major meta-analytic approaches using actual datasets, as well as the staistical forumulas for each approach and the methodological differences between each approach.
    • based upon which meta-analytic approach you choose to use, see (Lipsey & Wilson, 2001) for the Hedges/Olkin approach, see (Rosenthal, 1991) for the information on the Rosenthal/Rubin approach, or see (Hunter, Schmidt, & Jackson, 1982) for the Hunter/Schmidt/Jackson approach.



What is a meta-analysis?

Definition

A meta-analysis statistically combines the results of several studies that address a shared research hypotheses.

Just as individual studies summarize data collected from many individual participants in order to answer a specific research question (e.g., each participant is a separate data point), a meta-analysis summarizes data from individual studies that concern a specific research question (e.g., each data point is each individual study).

The results of each individual study are converted to a standardized effect size. A meta-analysis combines...


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 (variability), then we look for moderating variables that explain the variability. 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 – First you must have a well-defined statement of the relationship between the variables under investigation so that you can carefully define the inclusion and exclusion criteria when locating potential studies. Chapter 2 of

From readhing literature, define, set boundaries, etc.

  1. Locate the Literature – The central
  2. Identify and input data – Gather empiricial findings from primary studies (e.g., p-value, effect size, etc) and input into statistical database.
  3. Cacluate Effect Sizes – Calculate the overall effect -- effect size, significance level or confidence intervals associated with the effect size, and variaiblity (homogeneity) of the effect.
  4. Analyze Variables – Code your study variables, input the data into the database, and analyze the results. There are two types of study variables: (a) objective variables -- such as type of IV or DV, ..., (b) subjective variables -- inferential judgements made by two or more judges....

How do I conduct a meta-analysis?

First, choose which 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 – see (Hedges, 1981); (Hedges, 1982); (Hedges & Olkin, 1985)
  2. Rosenthal & Rubin Approach – see (Rosenthal, 1991); (Rosenthal & Rubin, 1978); (Rosenthal & Rubin, 1988)
  3. Hunter, Schmidt, & Jackson - see (Hunter, Schmidt, & Jackson, 1982); (Hunter & Schmidt, 1990)
Table1JMS2.gif

Second, choose which effect size to calculate?

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Third, choose your statistical software

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DSTAT calculates all of this for you Can also use SPSS and macros from “Practical Meta-Analysis” Calculate Categorical variables – DSTAT using weighted ANOVA Calculate Continuous variables – SPSS using weighted Regression


If you want more detailed information about...

...the Hedges & Olkin approach...

...the Rosenthal & Rubin approach...

...the Hunter, Schmidt, & Jackson approach...













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