Transcript Slide 1

Meta-analysis
Overview
www.psychwiki.com/wiki/Meta-analysis_club_Summer2008
Definition
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Definition
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A meta-analysis statistically combines the results of
several studies that address a shared research
hypotheses.
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A study collects data from individual subjects
(such as 100 subjects = 100 “data points”)
A meta-analysis collects data from individual studies
(such as 100 studies = 100 “data points”)
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Steps
1.Defines your hypothesis
2.Locate Studies
3.Find “effect size” for each study
4.Average the “effect sizes” together
5.If you want, you can analyze “moderators”
6.Write the manuscript
Why do a meta-analysis?
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Easy
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Cost-effective
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Steps are simple, there is software to calculate everything
Since you have already read a bunch of articles to write a
paper, not much more work to synthesize them together
Best type of article
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Most highly cited type of article.
Advantages of both qualitative and quantitative research
Truly answers research questions within the literature
(compared to single studies which can’t truly generalize)
Step 2 (again)
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Locate studies
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Techniques - database searches, ancestry
approach, descendancy approach, hand
searching, invisible college
Doesn’t have to be comprehensive (fail-safe n)
but needs to be close to comprehensive
(create excel file – example)
* so that you can Search it, copy/paste into References
Step 3 (again)
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Find “effect size” for each study
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(1) Decide: convert into “r” or “d”
(2) Download “es_calculator.zip” from
http://mason.gmu.edu/~dwilsonb/ma.html
(3) Use “es_calculator” to calculate ES
(4) Record in excel file, separate row for each study
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(excel file – example)
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* need to input sample size and ES
Step 4 (again)
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Average the “effect sizes” together
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Conceptually…
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First, weight them by sample size/inverse variance
Second, sum them together
Third, divide by sum of total sample size.
In Practice…
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You calculate inverse variance
Then use Macro to do the rest
Download macro for SPSS
http://mason.gmu.edu/~dwilsonb/ma.html
Step 5 (again)
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If you want, you can analyze “moderators”
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Conceptually…
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Can test categorical moderators (categories like college
student versus actual juror) similar to ANOVA
Can test continuous moderators (such as length of
stimulus) similar to Regression
In Practice…
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Use macros downloaded from
http://mason.gmu.edu/~dwilsonb/ma.html
Macros exist for ANOVA & Regression
Some cool things about meta-analyses…
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-- Due: ES calculated for each study
-- How to average ES (4) and Moderators (5)
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-- Ongoing – Step (4) and Step (5)
-- How to graph results / filedrawer
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-- Overview of meta-analysis/summer
-- How to find Hypothesis (1)
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-- Due: analysis complete
-- How to write a meta-analysis paper
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-- Due: Studies Located
-- How to find “ES” for each study (3)
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-- Due: Hypothesis
-- How to Locate Studies (2), code Moderators
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-- Due: 1 draft emailed BEFORE meeting
-- Critique each others papers
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-- Due: 2st draft emailed BEFORE meeting
-- Critique each others papers
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USC
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