Reviewer ’s report  
 
Title: Relationship of Breastfeeding Duration with Joint Pain and Knee Osteoarthritis in 
Middle -aged  Korean Women: A Cross -sectional Study using the Korea National Health and 
Nutrition  Examination Survey  
 
Version: 0 Date: 16 Jun 2020  
 
Reviewer's report:  
 
This review is primarily statistical in nature.  
 
I applaud the authors for their use of this data source and for accounting for the complex 
survey  design (i.e., clustering, stratification, weighting) used to collect it.  
 
Line 34 and throughout: Please describe how 'inci dence' can be determined. Are you able to  
ascertain whether there has been prior joint pain and/or knee OA? If not, please use different  
terminology.  
 
Line 106: Please clarify why joint pain include multiple joints, while OA focuses on knee (as  
opposed to h ip or other joints).  
 
Line 110: Please describe how left and right knee assessments were managed within an 
individual.  
 
Line 113: How are total knee replacements coded and managed in the analysis?  
 
Line 117: Are these 'potential' confounders?  
 
Lines 124 -125: P lease cite a reference for these BMI classifications.  
 
Line 150: Please specify how this variable was managed for women who had not yet reached  
menopause.  
 
Line 159: Would it be worthwhile to evaluate these variables by level of the response 
variables as  well? 
 
Line 162: Please describe the extent of missing values for each variable.  
 
Line 164: Please include discussion of modeling that only adjusts for age, as well as 
additional  multivariable modeling adjusting for more variables.  
 
Line 166: Please provide the  full listing of confounders for which you are controlling. Also,  
please describe how the confounders were selected for inclusion in the logistic models.  
 
Line 167: Are there other important implications due to the varying mean ages across the 
groups?  
 
Line 168: Please provide the rationale for choosing the age cutpoint of 60 years.  
 
Line 178 and following: Please clarify whether these descriptives are weighted or 
unweighted.  
 
Line 196: Please include your approach for testing for trend in Methods.  
 
Line 206: Pl ease clarify whether this is 'prevalence' or 'incidence', and consistently use the  
appropriate terminology throughout.  
 
Line 305: Please reword this sentence to list both pain and OA as dependent variables.  
 
Line 310: Please include in your discussion of lim itations the nature of the assessment of pain  
according to the intermittent nature of pain and the wording of the question in the survey,  
including the timing.  
 
Line 322: Please reword, as the association for joint pain with breastfeeding duration were  
determined separately from the association for OA with breastfeeding duration. Hence, the  
association between joint pain and OA were not assessed simultaneously in these analyses.  
 
Table 1: Please indicate values and frequencies and percentages, unless otherwis e specified. 
Also,  please indicate whether these are weighted or unweighted values. The footnote would 
not seem to  apply for t -tests, as more than 2 categories are being compared.  
 
Table 2: Please clarify that the breastfeeding variables were included in se parate models. 
Also,  please include the full model output, including values for all terms in each model. 
Please indicate  whether any pairwise comparisons are statistically significant for comparisons 
other than with the  reference group (e.g., the abstract mentions 25 -48 years versus >=49 
years); also, please mention  this approach in the Methods.  
 
Table 3: The same comments as for Table 2 apply here.  
 
Table 4: The same comments as for Table 2 apply here.  
 
Table 5: The same comments as for Table 2 apply here.  
 
 
Are the methods appropriate and well described?  
If not, please specify what is required in your comments to the authors.  
 
No 
 
Does the work include the necessary controls?  
If not, please specify which controls 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.  
 
Yes 
 
Are you able to assess any statistics in the manuscript or would you recommend an  
additional statistical review?  
If an additiona l 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 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 years received reimbursements, fees, funding, or salary from 
an organisation that may in any way gai n 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 any way gain or lose  
financially from the publication of this manuscript, either now or in the fu ture?  
 
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 o f 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 interested.  
 
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