Welcome to the sixth newsletter for the Cochrane Statistical Methods Group

Issue 6 September 2026

Methodology Webinars

In partnership with Cochrane Training, we have hosted two webinars, and have a third arranged for November. These webinars highlight methodological developments in evidence synthesis, with a focus on improving the application and interpretation of meta-analytic methods. Summaries of each webinar are provided below.

Upcoming webinar

Reflections on the I-squared index for measuring inconsistency in meta-analysis

Presenter: Julian Higgins | Professor of Evidence Synthesis at the University of Bristol, UK
Tuesday 17th November 09:00 – 10:00 UTC

The I-squared index was proposed in 2002 as a measure to help understand the consistency of study results in a meta-analysis. It was developed to overcome some of the limitations of existing measures, principally the chi-squared test for heterogeneity and the between-study variance as estimated in a random-effects meta-analysis.

In this webinar, Professor Higgins will reflect on the I-squared index and the different ways it can be defined, computed, and interpreted. He will explain why he believes many systematic reviews use the index inappropriately and will provide recommendations on how it should be used.

Associated publication DOI: 10.1017/rsm.2025.10062

Previous webinars 

Modelling departures from normality in meta-analysis 

Presenter: Dr. Kanella Panagiotopoulou | Institute of Medical Biometry and Statistics (IMBI), Faculty of Medicine and Medical Center—University of Freiburg, Germany

This webinar explored extensions to random-effects meta-analysis when the assumption of normally distributed study-specific effects may not be appropriate. The session introduced models that can uncover underlying data structures, such as asymmetry and clustering, which may be hidden under standard approaches. The presentation highlighted the role of these models as exploratory tools for better understanding complex patterns of heterogeneity in evidence synthesis. 

Associated publication DOI: 10.1186/s12874-025-02658-3

Producing treatment hierarchies in network meta-analysis using probabilistic models and treatment-choice criteria 

Presenter: Dr. Theodoros Evrenoglou| Institute of Medical Biometry and Statistics (IMBI), Faculty of Medicine and Medical Center—University of Freiburg, Germany

This webinar introduced a new probabilisitic framework for estimating treatment hierarchies in network meta-analysis based on clinically relevant treatment-choice criterion. The approach uses a latent ability parameter to represent each treatment’s propensity to produce clinically important benefits compared with other treatments in the network. The session also introduced the mtrank R package, providing a practical tool for implementing this alternative approach to treatment ranking.

Associated publication DOI: 10.1017/rsm.2026.10071

Please do send us suggestions of topics for future webinars.

Rare events working group

In November 2025, the Convenors of the SMG established a Rare Events Working Group to summarise the evidence on statistical approaches for handling rare events in meta-analysis,  with the purpose of developing recommendations for methods to be implemented in RevMan. Members of the SMG continue to work on this topic, and we are having ongoing discussions with the RevMan team regarding the evidence, methodological considerations, and potential approaches for implementation. These discussions will inform the development and refinement of recommendations as the work progresses.

Publications

Here we list some recent publications that might be of interest to the SMG membership. If you have a publication that you would like to be listed in our future newsletter, please get in contact (see details below).

• Behrens M, Nolde JM, Papakonstantinou E, et al. Distinguishing case-mix from context heterogeneity in prognostic regression model synthesis settings. arXiv. Preprint posted online August 14, 2026. doi: 10.48550/arxiv2608.12885
• Evrenoglou T, Nikolakopoulou A, Schwarzer G, et al. Producing treatment hierarchies in network meta-analysis using probabilistic models and treatment-choice criteria. Research Synthesis Methods. 2026;17(4):1-20. doi: 10.1017/rsm.2026.10071 
• Higgins JPT, López-López JA. Reflections on the I-squared index for measuring inconsistency in meta-analysis. Research Synthesis Methods. 2026;17(3):389-402. doi: 10.1017/rsm.2025.10062
• Konstantinidis M, Kontouli KM, Zhelnov P, et al. Characterizing updated and living meta-analyses Part 1: A methodological scoping review on methods for conducting meta-analyses in updated and living systematic reviews. Journal of Clinical Epidemiology. 2026;197:112389. doi: 10.1016/j.jclinepi.2026.112389
• Kwarteng N, Evrenoglou T, Mueller J, et al. Illustrating the assumptions of meta-regression in treatment networks. In Review. Preprint posted online February 24, 2026. doi: 10.21203/rs.3.rs-8235913/v1
• Kwarteng N, Schwarzer G, Nikolakopoulou A, Evrenoglou T. Assessing the impact of model assumptions in network meta-regression: A simulation study. arXiv. Preprint posted online July 21, 2026. doi: 10.48550/arxiv.2607.17750
• Panagiotopoulou K, Binder H, Evrenoglou T. Learning study similarity to investigate heterogeneity in meta-analysis using LLMs and triplet loss. arXiv. Preprint posted online May 26, 2026. doi: 10.48550/arXiv.2605.29603
• Panagiotopoulou K, Evrenoglou T, Schmid CH, et al. Meta-analysis models relaxing the random-effects normality assumption: methodological systematic review and simulation study. BMC Medical Research Methodology. 2025;25(1):231. doi: 10.1186/s12874-025-02658-3
• Sasaki K, Noma H, Evrenoglou T. Robust inference methods of diagnostic test accuracy meta-analysis for influential outlying studies via density power divergence. arXiv. Preprint posted online April 30, 2026. doi: 10.48550/arXiv/2604.27409
• Veroniki AA, Wolfe D, Hutton B, et al. Analysing complex interventions using component network meta- analysis. BMJ. 2026;393:e083075. doi: 10.1136/bmj-2024-083075

Contact us

Convenors: 

Joanne McKenzie, Australia
Mark Simmonds, UK
Areti Angeliki (Argie) Veroniki, USA

Theodoros Evrenoglou, Germany

Joseph Santos, Switzerland

Lizzie Korevaar, Australia

For details about how to post to the SMGlist, or how to unsubscribe from the list, please go to: https://lists.cochrane.org/mailman/listinfo/smglist