Review for 10.1186/s12876-016-0457-9 (2016)

Reviewer’s report  
Title: Comparison of the effectiveness of polyethylene glycol with and without electrolytes in  
constipation: a systematic review and network meta -analysis  
 
Version: 0 Date: 18 Nov 2015  
 
Reviewer: Nick Burr  
Reviewer’s report:  
Comparison of the effectiveness of polyethylene glycol with and without electrolytes in 
constipation: a systematic review and network meta -analysis  
 
Overall I think that the paper is clear, concise and easy to follow. I have concerns that the clinical 
question may not be in doubt. I would not expect the addition of electrolytes to affect the clinical 
effectiveness of PEG and there is no evidence presen ted to support a hypothesised difference. 
The question would be does it prevent electrolyte imbalance when used in the long term. The 
other question that is addressed in the secondary analyses is pertinent in that is the PEG tolerated 
and better adhered to  without the addition of electrolytes.  
 
Further specific points below  
 
Background  
 
No information on the possible physiological and clinical effects of the addition of electrolytes.  
Why would a clinician choose one over the other?  
Is there an optimal molecular weight for of the PEG?  
 
Search  
 
Conference proceedings not included.  
 
Data extraction  
 
"Converting to the median where mean not available".  As mentioned below this might not be 
comparable.  
Which statistical software/package was  used for the analyses?  
 
Results  
 
I feel that subgroup analyses would have been a useful inclusion, although preferable to perform 
these as pre -specified analyses. Although not always possible with low numbers it would be 
useful to mention this as a limitat ion. 
 
* Compare low and high doses.  
 
* Compare length of treatment - long term versus short term  
 
* Compare by indication - not sure that indications have been properly selected and coded.  
 
* Compare 3550 to 4000  
 
Limitation  
 
"Mean==median in a normal distribut ion". Agree but this might not be a normal distribution.  
 
Discussion  
 
Long term effects of reduced electrolytes??  
 
Table 1  
 
Stool frequency column not clear, ? parentheses  
Need consistency in the table entries - "history", "constipation", "history of const ipation", 
"history of" - are these similar??  
 
Why do some studies have values for comparator and placebo and others not? E.G. age, stool 
freq. 
 
Study groups comparable column not needed - RCTs  
?? ambulatory group, what does this mean  
 
Assessment time and study length - not clear why they are different  
 
Direct results for PEG E - PEG Forrest - change scale please.  
 
Table 4  
 
I would suggest removing this table and transpose the key points into the text (most there 
already).  
 
Spelling, gram mar and syntax  
Page numbers!  
Two full stops line 17 page 10  
Page 10 line 28 - reference error  
 
Competing interest - funded by key pharmaceuticals (Osmolax)  
 
Are the methods appropriate and well described?  
If not, please specify what is required in your comments to the authors.  
 
Yes 
 
Does the work include the necessary controls?  
If not, please specify which con trols are required in your comments to the authors.  
 
Yes 
 
Are the conclusions drawn adequately supported by the data shown?  
If not, please explain in your comments to the authors.  
 
No 
 
Are you able to assess any statistics in the manuscript or would you r ecommend an 
additional statistical review?  
If an additional statistical review is recommended, please specify what aspects require further 
assessment in your comments to the editors.  
 
I am able to assess the statistics  
 
Quality of written English  
Please in dicate the quality of language in the manuscript:  
 
Acceptable  
 
Declaration of competing interests  
Please complete a declaration of competing interests, consideri ng the following questions:  
 
1. Have you in the past five years received reimbursements, fees, fun ding, or salary from an 
organisation that may in any way gain or lose financially from the publication of this 
manuscript, e ither now or in the future?  
 
2. Do you hold any stocks or shares in an organisation that may in any way gain or lose 
financially from t he publication of this manuscript, e ither now or in the future?  
 
3. Do you hold or are you currently applying for any patents relating to the  content of the 
manuscript?  
 
4. Have you received reimbursements, fees, funding, or salary from an organization that 
holds or has applied for patents relating to the  content of the manuscript?  
 
5. Do you have any other fin ancial competing interests?  
 
6. Do you have any non -financial competing interests  in relation to this paper?  
 
If you can answer no to all of the above, write 'I declare that I have no competing interests' 
below. If your reply is yes to any, please give details below.  
 
I declare that I have no competing interests  
 
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