Meta-analysis
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==Where should I start?== | ==Where should I start?== | ||
- | If you want to learn | + | |
- | + | <TABLE BORDER=1 CELLSPACING=0 CELLPADDING=5> | |
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- | + | If you want to learn '''what is a meta-analysis'''... | |
- | + | <ol> | |
- | + | <li>For the <u>basics</u>, see below where we lay out:</li> | |
+ | *the [[#Definition | definition]] of a meta-anlaysis, | ||
+ | *the [[#Three Basic Questions | three basic questions]] answered by a meta, | ||
+ | *the [[#Five Basic Steps | the five steps]] involved in a meta-analysis, | ||
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+ | <li>For more <u>in-depth</u> discussion and explanations, we recommend...</li> | ||
+ | *start first with | ||
+ | * | ||
+ | * | ||
+ | </ol> | ||
+ | </TD> | ||
+ | <TD valign=top width=370> | ||
+ | If you want to learn '''how to start conducting a meta-analysis'''... | ||
+ | <ol> | ||
+ | <li>For the <u>basics</u>, see below were we lay out:</li> | ||
+ | *how to [[#First, choose what statistical approach suits your needs | choose a statistical approach]] | ||
+ | *how to [[#Second, choose which effect size to calculate? | choose which effect size to calculate]] | ||
+ | *how to [[#Third, choose your statistical software | choose your statistical software]] | ||
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+ | <li>For more <u>in-depth</u> discussion and explanations, we recommend...</li> | ||
+ | *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. | ||
+ | * | ||
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+ | </TD> | ||
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===Second, choose which effect size to calculate?=== | ===Second, choose which effect size to calculate?=== | ||
- | ===Third, choose your | + | ===Third, choose your statistical software=== |
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===If you want to follow the Hedges & Olkin approach...=== | ===If you want to follow the Hedges & Olkin approach...=== | ||
Revision as of 02:12, 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
Where should I start?
If you want to learn what is a meta-analysis...
|
If you want to learn how to start conducting a meta-analysis...
|
What is a meta-analysis?
Definition
Three Basic Questions
- A meta-analysis answers three general questions:
- 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?
- 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.
- 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:
- 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
- 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:
- Hedges & Olkin Approach – see (Hedges, 1981); (Hedges, 1982); (Hedges & Olkin, 1985)
- Rosenthal & Rubin Approach – see (Rosenthal, 1991); (Rosenthal & Rubin, 1978); (Rosenthal & Rubin, 1988)
- Hunter, Schmidt, & Jackson - see (Hunter, Schmidt, & Jackson, 1982); (Hunter & Schmidt, 1990)
Second, choose which effect size to calculate?
Third, choose your statistical software
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
- What is the good number of studies to have bare minimum for a meta-analysis? A meta-analysis with 10 studies have been published before but is not recommended.
- In a meta-analysis, don’t have raters code conditions for which no effect sizes can be calculated.
- In a meta-analysis, have judge rate each variable across studies, one moderator at a time, instead of rating all variables in a single study before moving on to next study.
- With meta-analysis coding with a high number of studies to code, such as 75+, can have some coders rate the entire set, but can also have some coders (undergrads) code only a subset as long there is overlap, so that more than 1 judge is rating each study.
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