Review for 10.1186/s12876-017-0662-1 (2017)

Reviewer ’s report  
 
Title: Partially covered metal stents have longer patency than uncovered and fully covered metal  
stents in the m anagement of distal malignant biliary obstruction: A retrospective study  
 
Version: 0 Date: 30 Jan 2017  
 
Reviewer: David Diehl  
 
Reviewer's report:  
 
This manuscript is a retrospective comparison between uncovered, fully covered and partially 
covered W allFlex stents for the treatment of distal biliary malignancy.  The authors 
retrospectively calculated stent patencies; they found that the partially covered stents had longest 
patency.  
 
 
The difference can be explained due to an unusually high migration ra te of the fully covered 
stents, more than 30%.  The reason for this is not clear. The title of the manuscript is a little 
misleading; perhaps it ought to be something like "Fully covered SEMS have shorter patency 
compared to partially covered due to excess ive stent migration"  
 
 
The major limitations of this study are its retrospective design.  No power analysis is done to see 
what sort of numbers would be necessary to compare the groups.  Furthermore, whether the 
cases were consecutive or not is not stated; this could introduce significant bias.  
 
 
The stent diameter used is nowhere stated in the manuscript; these stents are available in 8mm 
and 10mm sizes.  I am wondering if the high migration rate could be due to use of the smaller 
diameter stent; please incl ude the information on stent diameter.  
 
 
The above limitations make it very hard to reach conclusions about the data.  
 
 
The data analyses are sufficiently advanced that a statistical consultant is required to review the 
statistical methods.  
 
 
Figure 2 and 3 a re so similar, would consider just including one and mentioning the other in the 
text. 
 
 
 
 
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 controls are required in your comments to the authors.  
 
Unable to assess  
 
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 st atistics in the manuscript or would you recommend 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 recommend additional statistical review  
 
Quality of written English  
Please indicate the quality of language in the manuscript:  
 
Acceptable  
 
Declaration of competing interests  
Please complete a declaration of competing interests, considering the following questions:  
 
1. Have you in the past five year s received reimbursements, fees, funding, or salary from an  
organisation that may in any way gain or lose financially from the publication of this  
manuscript, either now or in the future?  
 
2. Do you hold any stocks or shares in an organisation that may in a ny way gain or lose  
financially from the publication of this manuscript, either 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 financial 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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on my report to the authors and, if the manuscript is accepted for publication, my named report  
including any attachments I upload will be posted on the website along with the authors'  
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to the editors, which will not be published.  
 
I agree to the open peer review policy of the journal