Meta-analysis is a quantitative research technique that aims to find the results by pooling data from multiple studies to arrive at one combined answer.
The field of psychology is diverse. There are many opposing theories and divergent findings published when examining different topics. For example, some research has shown that a particular drug has a positive effect against depression, while other studies show that the drug has no effect. So, scientists must interpret the results of any study in the context of its limitations.
Developed in the mid-1970s, meta-analysis has become a very useful methodological tool for accumulating research on a given topic for the past few decades. The meta-analysis integrates results from all published studies on the same topic. Here the sample size is the number of studies regarding the same research question, which in turn helps overcome the issue of small sample sizes.
Steps of meta-analysis
There are six steps involved in meta-analysis: (1) Defining the research question; (2) literature search; (3) coding of studies; (4) calculating an effect-size index; (5) statistical analysis and interpretation, and (6) publication (Sánchez-Meca, 2010; Cooper, 2010; Egger, Davey Smith, & Altman, 2001; Lipsey & Wilson, 2001; Littell, Corcoran, & Pillai, 2008; SánchezMeca & Marín-Martínez, 2010.)
1. Defining the research questions
Like every other research study, a meta-analysis starts with research questions. Any given meta analysis should focus on only one metric at a time. The research question should be defined as clearly and objectively as possible.
2. Literature search
After determining the research questions, the next step is to review the various studies related to the topic. It is also advised to search electronic databases like PsycInfo, MedLine, and ERIC. Similarly, searching conference proceedings, reference lists of relevant studies, and directly contacting the researchers are also helpful in metaanalysis.
3. Coding of studies
It involves recording the main characteristics of the study. The coding norms of the variables are written in a codebook. Variable is the characteristics of the studies. It is important to note that some characteristics are difficult to code due to incompleteness or ambiguity in the studies.
4. Calculating an effect-size index
After assembling all the necessary data, the fourth step is to calculate a summary from each study for further analysis. These measurements represent the difference in average scores between the intervention and control groups, referred to as Effect Sizes.
Some research findings must be given more weight than others. Studies that have larger sample sizes are more likely to provide precise effect sizes in comparison to the smaller studies. (BMJ)
5. Statistical analysis and interpretation
In a meta-analysis, the dataset is a matrix with rows representing studies and columns representing moderator factors. Each study’s impact size and sampling variance are calculated.
We then calculate the average effect-size index and confidence interval using this data. We also aim to assess the heterogeneity of the effect sizes around the average and search for the moderator variables that can explain the heterogeneity. (Sutton & Higgins, 2008)
Finally, the results of metaanalysis are then published in the standard format.
References and further readings
- Cooper, H. (2010). Research synthesis and meta-analysis: A step-by-step approach (3rd ed.). Thousand Oaks, CA: Sage.
2. Egger, M., Davey Smith, G., & Altman, D. G. (Eds.) (2001). Systematic reviews in health care: Meta-analysis in context (2nd ed.). London: BMJ Pub. Group.
3. Lipsey, M. W., & Wilson, D. B. (2001). Practical Meta-analysis. Thousand Oaks, CA: Sage
4. Littell, J. H., Corcoran, J., & Pillai, V. (2008). Systematic reviews and meta-analysis. Oxford, UK: Oxford University Press.
5. Rosenthal, R., & DiMatteo, M. R. (2001). Meta-Analysis: Recent Developments in Quantitative Methods for Literature Reviews. Annual Review of Psychology, 52(1), 59–82. https://doi.org/10.1146/annurev.psych.52.1.59
6. Sánchez-Meca, J., & Marín-Martínez, F. (2010). Meta-analysis in psychological research. International Journal of Psychological Research, 3(1), 150–162. https://doi.org/10.21500/20112084.860
7. Shorten, A., & Shorten, B. (2012). What is meta-analysis? Evidence Based Nursing, 16(1), 3–4. https://doi.org/10.1136/eb-2012-101118
8. Sutton, A. J., & Higgins, J. P. T. (2008). Recent developments in meta-analysis. Statistics in Medicine, 27, 625-650.
9. Very Well Mind. (2020). The Role of Meta-Analysis in Scientific Studies. https://www.verywellmind.com/definition-of-meta-analysis-425254
10. Wilson, L. C. (2014, September 30). Introduction to Meta-Analysis: A Guide for the Novice. Association for Psychological Science – APS. https://www.psychologicalscience.org/observer/introduction-to-meta-analysis-a-guide-for-the-novice