Not every study reports an SD. Can I use studies that give a 95% or 90% CI instead?

Yes. The SD can be converted from either a 95% CI or a 90% CI, but you will need to do this part by hand: convert everything to SDs, and then enter them into CMA.

For a CI around one group's mean, SD = √n × (upper limit − lower limit) ÷ 3.92 for a 95% CI, and ÷ 3.29 for a 90% CI. These numbers assume a large group. When a group is small (the Handbook suggests fewer than about 60 participants), replace them with the corresponding values from the t distribution with n − 1 degrees of freedom. If the CI is for the difference between two groups rather than for one group's mean, use Section 6.5.2.3 instead.

For the detailed formulas and worked examples, see the link below. This is the well-known Cochrane Handbook, Chapter 6, and you can cite it directly.

• Section 6.5.2.2, Obtaining standard deviations from standard errors and confidence intervals for group means: https://www.cochrane.org/authors/handbooks-and-manuals/handbook/current/chapter-06#section-6-5-2-2

The Cochrane Handbook offers advice for many difficult situations, such as conversions and estimation, and it is easy to cite. If you run into trouble, search there. These are the chapters I use and cite most often (version 6.5, current as of 2026):

• Higgins JPT, Li T, Deeks JJ (editors). Chapter 6: Choosing effect measures and computing estimates of effect (last updated August 2023). In: Cochrane Handbook for Systematic Reviews of Interventions, version 6.5. Cochrane, 2024.
• Deeks JJ, Higgins JPT, Altman DG, McKenzie JE, Veroniki AA (editors). Chapter 10: Analysing data and undertaking meta-analyses (last updated November 2024). In: Cochrane Handbook for Systematic Reviews of Interventions, version 6.5. Cochrane, 2024.
• Chaimani A, Caldwell DM, Li T, Higgins JPT, Salanti G. Chapter 11: Undertaking network meta-analyses (last updated October 2019). In: Cochrane Handbook for Systematic Reviews of Interventions, version 6.5. Cochrane, 2024.
• Page MJ, Higgins JPT, Sterne JAC. Chapter 13: Assessing risk of bias due to missing evidence in a meta-analysis (last updated August 2024). In: Cochrane Handbook for Systematic Reviews of Interventions, version 6.5. Cochrane, 2024.
• Higgins JPT, Eldridge S, Li T. Chapter 23: Including variants on randomized trials (last updated October 2019). In: Cochrane Handbook for Systematic Reviews of Interventions, version 6.5. Cochrane, 2024.