Letters To The Editor Open Access
Copyright ©The Author(s) 2015. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Jan 7, 2015; 21(1): 377-378
Published online Jan 7, 2015. doi: 10.3748/wjg.v21.i1.377
Re: ''Laparoscopic vs open approach to resection of hepatocellular carcinoma in patients with known cirrhosis: Systematic review and meta-analysis''
Zhan-Zhan Li, Li-Zhang Chen, Department of Epidemiology and Health Statistics, School of Public Health, Central South University, Changsha 410078, Hunan Province, China
Author contributions: Li ZZ and Chen LZ conceived the study, participated in the study design, collected the data, and drafted the manuscript; all authors read and approved the final manuscript.
Supported by Hunan Province Science and Technology Project, No. 2014SK2013; Fundamental Research Funds for the Central Universities of Central South University, No. 2014zzts069
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Correspondence to: Li-Zhang Chen, PhD, Department of Epidemiology and Health Statistics, School of Public Health, Central South University, No. 238 Shang Ma Yuan Ling Xiang Xiangya Road, Kaifu District, Changsha 410078, Hunan Province, China. liche4005@126.com
Telephone: +86-731-88836996 Fax: +86-731-88836162
Received: July 7, 2014
Peer-review started: July 8, 2014
First decision: August 6, 2014
Revised: August 23, 2014
Accepted: September 29, 2014
Article in press: September 30, 2014
Published online: January 7, 2015

Abstract

Twaij and colleagues have carried out a meta-analysis of cohort studies to review the currently available literature comparing laparoscopic to open resection of hepatocellular carcinoma in patients with known liver cirrhosis. We congratulate and applaud their important work, but several important issues should be noted.

Key Words: Meta-analysis, Standardized mean difference, Heterogeneity, Weighted mean difference, Sensitivity analysis

Core tip: The combination of effect sizes in the meta-analysis is based on several factors: type of design of included studies, type of data, heterogeneity among studies, numerical stability and accuracy and understandability of results. For continuous variables, the standard mean difference is recommended when different measurement scales in the studies are used to reflect the outcomes. However, the weighted mean difference is more suitable when studies included use the same scale to report the outcomes.
TO THE EDITOR

Twaij et al[1] have carried out a meta-analysis of cohort studies to review the currently available literature comparing laparoscopic to open resection of hepatocellular carcinoma in patients with known liver cirrhosis. We congratulate and applaud their important work, but several important issues should be noted.

First, in the “Statistical analysis” subsection of the paper, the author stated “to compute standard mean differences (SMD) for continuous variables”. The combination of effect sizes in the meta-analysis is based on several factors: type of design of included studies, type of data, heterogeneity among studies, numerical stability and accuracy and understandability of results. For continuous variables, the SMD is recommended when different measurement scales in the studies are used to reflect the outcomes. However, the weighted mean difference (WMD) is more suitable when studies included use the same scale to report the outcomes[2]. However, information from the four studies suggests that the scale of the outcomes is the same for continuous variables. The WMD should be applied in this meta-analysis.

Second, in the “Statistical analysis” subsection again, the authors stated “Meta-analysis of results was performed using a random effects model… and I2 test was used to assess data heterogeneity”. What is the meaning of data heterogeneity? I2 > 50% or something else? It is ambiguous and the authors need to clarify.

Third, in Table 1, the study by Belli et al[3] has a rate of conversion to open of only 7%, but accounts for 76.19% (blood transfusions), 46.88% (morbidity) and 41.27% (length of stay) of the total weights in Figures 4, 5 and 6, respectively. The authors should perform sensitivity analysis by omitting the study by Belli et al[3] to test the robustness of their results.

Footnotes

P- Reviewer: Morise Z, Solinas A S- Editor: Ma YJ L- Editor: Wang TQ E- Editor: Wang CH

References
1.  Twaij A, Pucher PH, Sodergren MH, Gall T, Darzi A, Jiao LR. Laparoscopic vs open approach to resection of hepatocellular carcinoma in patients with known cirrhosis: systematic review and meta-analysis. World J Gastroenterol. 2014;20:8274-8281.  [PubMed]  [DOI]  [Cited in This Article: ]  [Cited by in CrossRef: 77]  [Cited by in F6Publishing: 81]  [Article Influence: 8.1]  [Reference Citation Analysis (1)]
2.  Higgins JPT, Green S, editors . Cochrane Handbook for Systematic Reviews of Interventions 4.2.6. Chichester, UK: John Wiley & Sons, Ltd 2006; .  [PubMed]  [DOI]  [Cited in This Article: ]
3.  Belli G, Limongelli P, Fantini C, D’Agostino A, Cioffi L, Belli A, Russo G. Laparoscopic and open treatment of hepatocellular carcinoma in patients with cirrhosis. Br J Surg. 2009;96:1041-1048.  [PubMed]  [DOI]  [Cited in This Article: ]  [Cited by in Crossref: 153]  [Cited by in F6Publishing: 166]  [Article Influence: 11.1]  [Reference Citation Analysis (0)]