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How to obtain nnt from cohen’s D: comparison of two methods
Open accessAbstract
BACKGROUND: In the literature we find many indices of size of treatment effect (effect size: ES). The preferred index of treatment effect in evidence-based medicine is the number needed to treat (NNT), while the most common one in the medical literature is Cohen's d when the outcome is continuous. There is confusion about how to convert Cohen's d into NNT. METHODS: We conducted meta-analyses of individual patient data from 10 randomized controlled trials of second generation antipsychotics for schizophrenia (n = 4278) to produce Cohen's d and NNTs for various definitions of response, using cutoffs of 10% through 90% reduction on the symptom severity scale. These actual NNTs were compared with NNTs calculated from Cohen's d according to two proposed methods in the literature (Kraemer, et al., Biological Psychiatry, 2006; Furukawa, Lancet, 1999). RESULTS: NNTs from Kraemer's method overlapped with the actual NNTs in 56%, while those based on Furukawa's method fell within the observed ranges of NNTs in 97% of the examined instances. For various definitions of response corresponding with 10% through 70% symptom reduction where we observed a non-small number of responders, the degree of agreement for the former method was at a chance level (ANOVA ICC of 0.12, p = 0.22) but that for the latter method was ANOVA ICC of 0.86 (95%CI: 0.55 to 0.95, p<0.01). CONCLUSIONS: Furukawa's method allows more accurate prediction of NNTs from Cohen's d. Kraemer's method gives a wrong impression that NNT is constant for a given d even when the event rate differs.
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“Based on a NNT of 2 for the main analyses this means that for every two people treated with exercise, it is expected at least one to have a large magnitude reduction in depressive symptoms.43”
From Exercise as medicine for depressive symptoms? A systematic review and meta-analysis with meta-regression (2023) · cites this paper as [43]
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Metadata
- Authors
- Furukawa, T. A., & Leucht, S.
- Affiliations
- Kyoto University (JP)
- TUM Klinikum (DE)
- Corresponding author
- Furukawa, Toshi A.
- Venue
- PLoS ONE
- Publisher
- Public Library of Science (PLoS)
- Published
- 2011-04-27
- Volume
- 6
- Issue
- 4
- Pages
- e19070
- ISSN
- 1932-6203 (ISSN-L)
- PMC
- PMC3083419
- OpenAlex
- W2057672284
- Cited by
- 179
- References
- 29
- Citations by year
- 2026: 9 · 2025: 18 · 2024: 23 · 2023: 14 · 2022: 8 · 2021: 12 · 2020: 20 · 2019: 14 · 2018: 25 · 2017: 6 · 2016: 8 · 2015: 6 · 2014: 5 · 2013: 6 · 2012: 3
- FWCI
- 5.47
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Locations
- PLoS ONE (publishedVersion, cc-by)
- Europe PMC (PubMed Central) (publishedVersion, cc-by)
- PubMed Central (publishedVersion, cc-by)
- PubMed (publishedVersion)
- Institutional Repositories DataBase (IRDB) (submittedVersion, other-oa)
- RePEc: Research Papers in Economics (submittedVersion)
- DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
- mediaTUM – the media and publications repository of the Technical University Munich (Technical University Munich) (submittedVersion)
- mediaTUM – the media and publications repository of the Technical University Munich (Technical University Munich) (submittedVersion, other-oa)
- Kyoto University Research Information Repository (Kyoto University) (submittedVersion, cc-by)
- Funders
- American Psychiatric Publishing
- Bristol-Myers Squibb
- Eli Lilly and Company
- Pfizer
- AstraZeneca
- GlaxoSmithKline
- Sanofi
- Astellas Pharma
- Shionogi
- H. Lundbeck A/S
- Topics
- Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Meta-analysis and systematic reviews
- Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Clinical Trials
- Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Epidemiology
- Keywords
- number needed to treat, Cohen's d, effect size, atypical antipsychotics, schizophrenia, symptom severity reduction, treatment response definition, interobserver agreement
- MeSH terms
- Humans, Schizophrenia, Antipsychotic Agents, Sample Size, Evidence-Based Medicine
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