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Title: Which is more generalizable, powerful and interpretable in meta-analyses, mean difference or standardized mean difference?
Authors: Takeshima, Nozomi
Sozu, Takashi  KAKEN_id
Tajika, Aran  kyouindb  KAKEN_id
Ogawa, Yusuke  kyouindb  KAKEN_id
Hayasaka, Yu
Furukawa, Toshiaki A  kyouindb  KAKEN_id  orcid https://orcid.org/0000-0003-2159-3776 (unconfirmed)
Author's alias: 竹島, 望
Issue Date: 21-Feb-2014
Publisher: BioMed Central
Journal title: BMC medical research methodology
Volume: 14
Thesis number: 30
Abstract: Background: To examine empirically whether the mean difference (MD) or the standardised mean difference (SMD) is more generalizable and statistically powerful in meta-analyses of continuous outcomes when the same unit is used. Methods: From all the Cochrane Database (March 2013), we identified systematic reviews that combined 3 or more randomised controlled trials (RCT) using the same continuous outcome. Generalizability was assessed using the I-squared (I2) and the percentage agreement. The percentage agreement was calculated by comparing the MD or SMD of each RCT with the corresponding MD or SMD from the meta-analysis of all the other RCTs. The statistical power was estimated using Z-scores. Meta-analyses were conducted using both random-effects and fixed-effect models. Results: 1068 meta-analyses were included. The I2 index was significantly smaller for the SMD than for the MD (P < 0.0001, sign test). For continuous outcomes, the current Cochrane reviews pooled some extremely heterogeneous results. When all these or less heterogeneous subsets of the reviews were examined, the SMD always showed a greater percentage agreement than the MD. When the I2 index was less than 30%, the percentage agreement was 55.3% for MD and 59.8% for SMD in the random-effects model and 53.0% and 59.8%, respectively, in the fixed effect model (both P < 0.0001, sign test). Although the Z-scores were larger for MD than for SMD, there were no differences in the percentage of statistical significance between MD and SMD in either model. Inclusions: The SMD was more generalizable than the MD. The MD had a greater statistical power than the SMD but did not result in material differences.
Rights: © 2014 Takeshima et al.; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
URI: http://hdl.handle.net/2433/185153
DOI(Published Version): 10.1186/1471-2288-14-30
PubMed ID: 24559167
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