# Meta-analysis

(Difference between revisions)
 Revision as of 00:12, 18 July 2006 (view source)Stenstro (Talk | contribs)← Older edit Revision as of 00:16, 18 July 2006 (view source)Stenstro (Talk | contribs) Newer edit → Line 2: Line 2: - ==Where should I start?== - If you want to learn what is a meta-analysis… - If you want to start conducting a meta-analysis… - There are generally three different statistical approaches to conduct a meta-analysis so first you need to choose which approach best fits your needs. + + ==Where should I start?== + *If you want to learn what is a meta-analysis... + *If you want to start conducting a meta-analysis... + :#There are generally three different statistical approaches to conduct a meta-analysis so first you need to choose which approach best fits your needs. Hedges & Olkin Approach – Hedges, 1981; Hedges, 1982; Hedges & Olkin, 1985 Hedges & Olkin Approach – Hedges, 1981; Hedges, 1982; Hedges & Olkin, 1985 Line 13: Line 14: Hunter, Schmidt, & - Hunter, Jackson, 1982; Hunter & Schmidt, 1990 Hunter, Schmidt, & - Hunter, Jackson, 1982; Hunter & Schmidt, 1990 - [[Image:Table1.gif]] + ::[[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

Meta-analysis

## Where should I start?

• If you want to learn what is a meta-analysis...
• If you want to start conducting a meta-analysis...
1. There are generally three different statistical approaches to conduct a meta-analysis so first you need to choose which approach best fits your needs.

Hedges & Olkin Approach – Hedges, 1981; Hedges, 1982; Hedges & Olkin, 1985

Rosenthal & Rubin Approach – Rosenthal, 1991; Rosenthal & Rubin, 1978; Rosenthal & Rubin, 1988

Hunter, Schmidt, & - Hunter, Jackson, 1982; Hunter & Schmidt, 1990

File: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

## What are the basic steps in conducting a meta-analysis?

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?

• 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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