Meta-analysis

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==If you want more detailed information about...==
==If you want more detailed information about...==
===...the Hedges & Olkin approach...===
===...the Hedges & Olkin approach...===
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* See [[Lipsey & Wilson, 2001]] (Practical Meta-Anlaysis) - which is relatively new book that provides a concise summary of all stages of the meta-analyses process, including providing ...
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* See [[Cooper & Hedges, 1994]] (Handbook of Research Synthesis) - which is great in-depth articuluation of every step involved in designing, analyzing, and writing-up a meta-analysis.
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* See [[Hedges & Olkin, 1985]] (Statistical Methods for Meta-Analysis) - which is the original source of information about the Hedges & Olkin approach.
===...the Rosenthal & Rubin approach...===
===...the Rosenthal & Rubin approach...===
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* See [[Rosenthal, 1991]] (Meta-analytic Procedures for Social Research) - which is the definitive source of information on the Rosenthal & Rubin approach.
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* See [[Rosenthal & DiMatteo, 2001]] (Meta-Analysis: Recent Developments in Quantitative Methods for Literature Reviews) - which is an updated summary of the Rosenthal approach.
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* See [[Rosenthal, 1995]] (Writing Meta-Analytic Reviews - which is an excellent Psychological Bulletin article on how to write a meta-analysis.
===...the Hunter, Schmidt, & Jackson approach...===
===...the Hunter, Schmidt, & Jackson approach...===

Revision as of 03:53, 18 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

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.



What is a meta-analysis?

Definition

A meta-analysis is...

combines the results of several studies that address a set of related research hypotheses.

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

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
  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 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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If you want more detailed information about...

...the Hedges & Olkin approach...

...the Rosenthal & Rubin approach...

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





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