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A meta-analysis is a quantitative technique that collects and combines the results of multiple studies to create a single estimate or result. This procedure uses a systematic method to collect and analyse data from multiple studies, comparing and contrasting the results to see if there is a unified conclusion. It is a summary, in effect, of numerous studies to form one piece of literature covering the area of study.
This research process identifies if the collective study’s findings support or disprove a hypothesis proposed by the research overall.
Research, flaticon.com/Freepik
What do we mean by a meta-analysis?
Meta-analysis is a research technique researchers frequently use in psychology.
A meta-analysis is a quantitative, systematic method that summarises the findings of multiple studies investigating similar phenomena.
Using a meta-analysis in research is useful when:
For instance, if a researcher wants to see if an overwhelming amount of research supports or disproves a theory.
Reviewing research, flaticon.com/premium-icon
When deciding to perform a meta-analysis of existing research, a researcher will typically:
Identify the area of research they are interested in
Form a hypothesis to investigate
Create an inclusion/exclusion criteria.
An inclusion criterion is a list of criteria that summarises key points that should be included in research that should be included in the meta-analysis.
An exclusion criterion is a list of criteria that point out characteristics of a study that should not be included in the meta-analysis.
For example, a meta-analysis investigating a healthy population will exclude studies investigating people diagnosed with mental health illnesses.
The inclusion/exclusion criteria should be centred around what is being researched and the research designs. The study’s findings should not be a part of it. If the criterion does this, the meta-analysis is likely to be biased and will affect the validity of the results.
Use a database to identify all of the research similar to what the hypothesis is investigating. Several established databases in psychology include published work. In this stage, researchers need to search key terms that summarise what the meta-analysis is investigating to identify studies that also investigated similar factors/ hypotheses.
This part essentially is what a systematic review is.
Determine which studies will be used based on the inclusion/exclusion criteria. From the studies found in the database, the researcher needs to determine if they should be included in the meta-analysis.
Studies included meeting the criteria of the inclusion criterion.
Studies excluded meeting the criteria of the exclusion criterion.
Appraise the research studies – the appraisal of studies is an essential stage in the meta-analysis methodology that involves checking the reliability and validity of the studies that meet the requirements of the inclusion criterion. Studies low in reliability or validity are usually not included in the meta-analysis.
Studies that are low in reliability/validity will also lower the reliability/validity of the meta-analysis findings.
Van Ijzendoorn and Krronenberg (1988) conducted a meta-analysis to investigate cultural differences in attachment styles. The meta-analysis statistical method they used was to calculate the mean scores of attachment styles. These mean scores were then compared across the different countries to identify cross-cultural differences in attachment styles.
Once they have compiled the information and statistically analysed the results, they can form a conclusion of whether the analysis supports/disproves the hypothesis initially proposed.
Van Ijzendoorn and Kroonenberg (1988) performed a meta-analysis to identify cross-cultural and intra-cultural differences between attachment styles.
The meta-analysis reviewed a total of 32 studies from eight different countries. The inclusion criteria of the meta-analysis were studies where:
The strange situation was used to identify attachment styles.
The studies investigated mother-infant attachment styles.
The studies used the same attachment classification system as in Ainsworth’s Strange Situation – type A (insecure avoidant), type B (secure), and type C (insecure avoidant).
Studies not meeting the meta-analysis requirements were excluded from the analysis. Furthermore, the exclusion criteria of studies recruiting participants with developmental disorders were excluded from the analysis. The researchers calculated each country’s average percentage and mean score of attachment styles.
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Researchers found that:
Secure attachments were the most common attachment style in each country analysed.
Western countries had a higher mean score of insecure-avoidant attachments than Eastern countries.
Eastern countries had a higher mean score of insecure-ambivalent attachments than Western countries.
This meta-analysis example shows the importance of meta-analysis in research. It allowed the researchers to compare data from multiple countries in a relatively fast and cheap way. This research may be difficult for the researchers to collect primary data from each of the eight countries due to cost and language barriers.
Meta-analysis and systematic review are common research techniques used in psychology. Although similar research processes, stark differences between the two exist where it counts.
Meta-analysis vs systematic review:
Systematic review is included in one of the stages of the meta-analysis methodology. This aspect of meta-analysis involves systematically collecting relevant studies from scientific databases that answer the research question. A systematic review also includes the stage of ensuring the studies included in the final analysis meet the requirements of the criterion.
A meta-analysis is a statistical research process that summarises the results of multiple studies that measure similar concepts. The critical part here is the inclusion and importance placed on the statistical analysis of the compiled results, something which a systematic review will not do.
Let’s discuss the advantages and disadvantages of a meta-analysis in psychology research.
The advantages of using a meta-analysis are:
It allows researchers to analyse data from a large sample. The results from the meta-analysis are more likely to be generalisable.
This method is relatively cheap, as the studies have already been conducted, and the results are already available.
Meta-analyses draw conclusions based on evidence from multiple empirical sources. Therefore, there is an increased likelihood meta-analysis findings will be more valid than independent experimental research that forms a conclusion based on a single study’s finding.
Meta-analysis in research has many practical applications in psychology. For example, it can provide a reliable, precise summary of whether an intervention is effective as a treatment method.
Beltman, Oude, Voshaar and Speckens (2010) did a meta-analysis of 29 published papers that met the study’s inclusion criteria.
The meta-analysis aimed to measure the effectiveness of cognitive-behavioural therapy as an intervention for depression in people with somatic diseases.
The meta-analysis found CBT significantly reduces depressive symptoms in people with various somatic diseases.
A somatic disease manifests when a person’s mental health symptoms, such as pain or digestive problems, manifest into physical health symptoms. Other physical or mental health illnesses cannot explain these symptoms.
The disadvantages of using a meta-analysis are:
Researchers need to ensure the research studies they are combining into their meta-analysis are reliable and valid, as this can affect the reliability and validity of the meta-analysis.
The different studies included in the meta-analysis will likely use different research designs, which raises the question of whether the data is comparable.
Meta-analysis needs to use research that is not heterogeneous, i.e. research needs to be similar for them to qualify as being comparable.
Although the researcher does not collect the data, the meta-analysis methodology can still be time-consuming. It will take time for researchers to identify all of the relevant research. In addition, they will need to identify if the studies are of acceptable standards in terms of reliability and validity.
Suppose the researcher is investigating a new area of research or a phenomenon that many researchers have not investigated before. In that case, it may not be appropriate to use a meta-analysis.
Esterhuizen and Thabane (2016) emphasised that meta-analyses are often criticised for including poor-quality research, comparing heterogeneous research and not addressing publication bias.
Publication bias is the idea that research results that are insignificant or show results against the existing knowledge in psychology are less likely to be published.
This publication bias in research can reduce the validity of findings in meta-analyses.
The criterion used may not be appropriate for the hypothesis and may incorrectly exclude or include studies in the meta-analysis, which will affect the meta-analysis results. Thus, careful consideration of what to include or exclude needs to be done, and it is not always perfect.
A meta-analysis is a quantitative, systematic method that summarises the findings of multiple studies that are investigating similar phenomena.
There are several stages of the meta-analysis methodology. These are:
Using a meta-analysis in research is useful when:
A systematic review is included in one of the stages of the meta-analysis methodology. This aspect of meta-analysis involves systematically collecting relevant studies from scientific databases that answer the research question. A systematic review also includes the stage of ensuring the studies included in the final analysis meet the requirements of the criterion. Whereas, meta-analysis is the technique that is used to summarise the results found from the systematic review, using statistical analysis techniques and processes.
Van Ijzendoorn and Kroonenberg (1988) carried out a meta-analysis to identify cross-cultural and intra-cultural differences between attachment styles.
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