Meta-analysis: a tool for clinical and experimental research in psychiatry

Methodological assessment and overall confidence in the results of systematic reviews with network meta-analyses in Endodontics

AIM

The aims of the study were to assess the methodological quality of systematic reviews with network meta-analyses (NMAs) in Endodontics using the "A MeaSurement Tool to Assess systematic Reviews" (AMSTAR 2) tool, and to evaluate the overall confidence in the results of the individual reviews included in the analysis.

METHODOLOGY

Systematic reviews with NMAs within the specialty of Endodontics published in English were identified from the PubMed, EbBSCOhost and SCOPUS databases from inception to July 2021. Two reviewers were involved independently in the selection of the reviews, data extraction, methodological quality assessment and overall confidence rating. Disagreements were resolved by discussion between the reviewers to achieve consensus; if disagreements persisted, a third reviewer made the final decision. The methodological quality of the included NMAs was appraised using the AMSTAR 2 checklist, which contains 16 items. The reviewers scored each item - 'Yes' - when the item was fully addressed, 'Partial Yes' - when the item was not fully addressed, or 'No' - when the item was not addressed. The overall confidence in the results of each review was classified as 'High', 'Moderate', 'Low' or 'Critically low' based on the criteria reported by the AMSTAR 2 developers.

RESULTS

Twelve systematic reviews with NMAs were included. All the NMAs adequately reported Item 1 ("Did the research questions and inclusion criteria for the review include the components of PICO?"), Item 8 ("Did the review authors describe the included studies in adequate detail?"), Item 9 ("Did the review authors use a satisfactory technique for assessing the risk of bias (RoB) in individual studies that were included in the review?") and Item 16 ("Did the review authors report any potential sources of conflict of interest, including any funding they received for conducting the review?") , whereas only one NMA reported Item 10 adequately ("Did the review authors report on the sources of funding for the studies included in the review?"). The overall confidence in the results of eight reviews was categorised as "Critically low", one review was "Low", two reviews were "Moderate" and one review was "High".

CONCLUSION

The overall confidence in the results for the majority of systematic reviews with NMAs in Endodontics was judged to be 'Critically low' as their methodological quality was below the necessary standard. AMSTAR 2 and PRISMA for NMA guidelines are available to guide authors to produce high quality systematic reviews with NMAs and for Editors and peer-reviewers when assessing submissions to journals.

Meta-Analysis for Epigenome-Wide Association Studies

With the rapid development of methylation profiling technology, many datasets are generated to quantify genome-wide methylation patterns. Given the heavy burden of multiple testing of hundreds of thousands of DNA methylation markers, individual studies often have limited sample sizes and power. The EWAS meta-analysis is an approach that combines results from multiple studies on the same scientific question. It helps to improve statistical power by combining information from individual studies and reduce the chances of false positives. This chapter introduces commonly used meta-analysis methods and analytical tools with application to EWAS data.

A novel estimator of between-study variance in random-effects models

BACKGROUND

With the rapid development of high-throughput sequencing technologies, many datasets on the same biological subject are generated. A meta-analysis is an approach that combines results from different studies on the same topic. The random-effects model in a meta-analysis enables the modeling of differences between studies by incorporating the between-study variance.

RESULTS

This paper proposes a moments estimator of the between-study variance that represents the across-study variation. A new random-effects method (DSLD2), which involves two-step estimation starting with the DSL estimate and the [Formula: see text] in the second step, is presented. The DSLD2 method is compared with 6 other meta-analysis methods based on effect sizes across 8 aspects under three hypothesis settings. The results show that DSLD2 is a suitable method for identifying differentially expressed genes under the first hypothesis. The DSLD2 method is also applied to Alzheimer's microarray datasets. The differentially expressed genes detected by the DSLD2 method are significantly enriched in neurological diseases.

CONCLUSIONS

The results from both simulationes and an application show that DSLD2 is a suitable method for detecting differentially expressed genes under the first hypothesis.

Meta-analyses of cavum septum pellucidum in mood disorders in comparison with healthy controls or schizophrenia

The cavum septum pellucidum (CSP) is a neurodevelopmental abnormality significantly more prevalent in subjects with schizophrenia (SCZ) than in healthy controls (HC). Using meta-analyses, we tested the hypotheses whether CSP would be more frequent in subjects with mood disorders when compared with HC or SCZ. We performed a search in MEDLINE and EMBASE followed by 10 meta-analyses of magnetic resonance imaging studies which examined the association of CSP in bipolar disorders (BD), major depressive disorder (MDD) or mood disorders (MD; considering MDD and BD combined) with either HC or SCZ. Nine studies were included, comprising 692 cases (363 with BD, 182 with MDD and 147 with MD), 463 with SCZ and 630 HC. CSP of any size was significantly associated with BD (OR = 2.07, 95% CI: 1.48-2.90) when compared with HC. Large CSP showed a trend to be associated with BD when compared with HC, but the association was not statistically significant (OR = 1.92, 95% CI 0.64-5.78). Large CSP was significantly associated with subjects with SCZ when compared with subjects with MD (OR = 0.57, 95% CI: 0.36-0.92). There was no association between CSP and MDD in comparison to HC or subjects with SCZ. Cortical structures are known to be altered in mood disorders. The present metanalysis found that certain midline brain abnormalities, such as CSP, are also associated with BD.

The role of COMT gene Val108/158Met polymorphism in suicidal behavior: systematic review and updated meta-analysis

BACKGROUND

It is accepted that there is a genetic factor that influences the risk of suicidal behavior. The catechol-O-methyltransferase (COMT) gene, especially the Val108/158Met polymorphism, has been associated with suicide; however, no conclusive outcome has been attained. Therefore, the aim of the present study was to assess the role of COMT Val108/158Met in suicidal behavior throughout an updated meta-analysis.

METHODS

We performed an online search using PubMed and Web of Science (up to March 2017). Our systematic review included case-control studies of individuals who attempted suicide and completed suicide. We tested allelic, homozygous, heterozygous, dominant, and recessive inheritance models. The meta-analysis was performed in accordance with the statement of Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

RESULTS

The meta-analysis comprised 17 studies, which included 3,282 cases and 3,774 controls, and showed that when evaluating the overall population, the Val108/158Met polymorphism of COMT was not associated with suicidal behavior in any of the inheritance models; however, the subanalyses showed that this polymorphism exhibits a risk factor in males and a protective effect in females. Additionally, it conveyed a risk factor in Asian populations when using the allelic (OR 1.25; CI: 1.04-1.51) and recessive models (OR 1.32; CI: 1.03-1.68).

CONCLUSION

Our updated meta-analysis suggests a possible association between COMT Val108/158Met and suicidal behavior in Asian populations. However, in view of the small number of studies, these results should be considered exploratory. We recommend that more studies be performed with larger samples.

The role of C957T, TaqI and Ser311Cys polymorphisms of the DRD2 gene in schizophrenia: systematic review and meta-analysis

Background

The association between the dopamine D2 receptor (DRD2) gene and schizophrenia has been studied though no conclusive outcomes have been attained. The aim of this study was to perform a systematic review and meta-analysis to explore the relation between three polymorphisms of the DRD2 gene (C957T, TaqI and Ser311Cys) and schizophrenia.

Methods

The search was made in PubMed and EBSCO databases (up to February 2016). The systematic review included 34 case–control association studies (34 for C957T, 16 for TaqI and 36 for Ser311Cys). The association analysis comprised the allelic, additive, dominant, and recessive genetic models. The meta-analysis was performed following the preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement.

Results

The meta-analysis showed that TaqI (additive model: OR 0.57, 95% CI 0.30–1.14) and C957T (additive model: OR 0.75, 95% OR 0.58–0.97, recessive model: OR 0.79, 95% CI 0.64–0.98) exert a protective effect against developing schizophrenia. However, the sub-analysis for the C957T variant showed that this polymorphism exhibits a risk factor effect on Chinese individuals (allelic model: OR 1.33, 95% CI 1.04–1.70).

Conclusion

Our meta-analysis suggests an association of the DRD2 gene and the risk for schizophrenia, given that TaqI and C957T polymorphisms presented a protective effect against schizophrenia, and in the sub-analyses the C957T variant increased the risk for this disorder in the Chinese population.

Electronic supplementary material

The online version of this article (doi:10.1186/s12993-016-0114-z) contains supplementary material, which is available to authorized users.