LETTER

Mean Values after Treatment or Mean Difference? 

Behnam Amani1, Arash Akbarzadeh2, Bahman Amani,1*

In a systematic review and meta-analysis Published in the Urology(1) entitled “Low-Intensity Extracorporeal Shock Wave Therapy for Erectile Dysfunction: a Systematic Review and Meta-Analysis” by Libo and Guizhong 
in 2017, the authors in methods section  state that “weighted mean difference (MD) was used for continuous var-
iables in their meta-analysis”. While, the authors used the endpoint scores as the mean difference in each group 
regardless of the baseline scores and one study(2) that baseline used as mean difference 
Based on statistical literature in meta-analysis, the “mean difference” is change average from baseline to endpoint. 
So, to calculate the mean difference, we should use endpoint minus baseline mean score(3).  
In our understanding, , it seems that the result of Libo’s meta-analysis(1) should revise for the mean difference as 
mentioned above.

REFERENCES
 1. Libo M, Guizhong L. Low-Intensity Extracorporeal Shock Wave Therapy for Erectile Dysfunction: a 

Systematic Review and Meta-Analysis. Urology. 2017.
 2. Vardi Y, Appel B, Kilchevsky A, Gruenwald I. Does low intensity extracorporeal shock wave therapy 

have a physiological effect on erectile function? Short-term results of a randomized, double-blind, sham 
controlled study. The Journal of urology. 2012 May;187(5):1769-75. PubMed PMID: 22425129. Epub 
2012/03/20. eng.

 3. Cooper H, Hedges LV, Valentine JC. The handbook of research synthesis and meta-analysis: Russell 
Sage Foundation; 2009.

1Department of Health Sciences Education Development, School of Public Health, Tehran University of Medical Sciences, Tehran, 
Iran.
2Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
Correspondence: Department of Health Sciences Education Development, School of Public Health, Tehran University of Medical 
Sciences, Tehran, Iran. Email: B-Amani@alumnus.tums.ac.ir  

Urology Journal/Vol 17 No. 3/ May-June 2020/ pp. 324-324. [DOI: 10.22037/uj.v0i0.4646]