Review for 10.1186/s12876-023-03029-2 (2023)

Title: The incidence of chronic diarrhea decreases with increasing serum calcium levels: a cross-
sectional study based on NHANES 2005-2010
Version: 1 Date: 21 Jul 2023
Reviewer's report:
Dear authors,
Please find my comments and suggestions as follows:
1) Title: The year is incorrect in the title. There should be space in between NHANES and the
year.
2) Introduction:  a) It's better to give a reference to the statement "Calcium is the most plentiful
mineral element in the human body".
b) It is not clear why the reference of 'colorectal cancer' was given. It would have been suitable
if you found examples of other gastrointestinal disorders to relate with diarrhea.
c) Your reasoning behind conducting this study is not clear. Please mention information such as
why the amount of total calcium in our body encouraged you to look, particularly, at diarrhea,
what's the relation of calcium and diarrhea.
d) I believe this is not a cross-sectional study. The NHANES survey was cross-sectional but
you are using the data from NHANES to conduct a secondary analysis. Therefore, the design
should be 'secondary analysis'.
3) Methods: a) Please use past tense in the methods section to describe what was done.
b) Be consistent. When talking about NHANES dataset, write all the information together.
c) Take care of punctuation marks and inconsistent sentences. For example, your sentences
"NHANES is a health screening program designed to assess the health and nutritional status
of US citizens.  Selecting Respondents  for a Representative Sample Using a Multilevel
Hierarchical Probability Model[9]." are not clear. Make sure to relate these two sentences.
d) Ethical approval: You need to talk about the ethical approval of your analysis, not the ethical
approval of NHANES survey. Tell us if you got an approval or it was not required based on
the study design.
e) Measurement of Serum Calcium: I am not sure why you needed to give this information
"When the sample buffer comes into contact with the electrode, calcium ions form complexes
with ionic groups on the electrode surface. As the reaction progresses, the surface potential of
the electrode changes. These potential changes are relative to the sodium reference electrode."
f) Bowel Health Questionnaire and definition of chronic diarrhea: I am not sure why you needed
to give this information "...researchers asked them, "Please look at this card and tell me your
most common stool type, or the numerical stool type corresponding to the most common stool
type"."
g) It is not clear why you chose "Marital status" and "Household income" as covariates. Please
explain.
4) Results: The heading "Serum calcium Affects the Risk of Patients With Diarrhea" is not clear,
please rephrase.
5) Overall comment on grammar: The manuscript has several grammatical errors such as spacing
issues, spelling mistakes (e.g., Many "studios" use Bristol stool scales), punctuation mark errors,
inconsistent sentences, wrong sentence structures, mixture of British and U.S. spellings, capital
letters in the middle of the sentence. I’d suggest a careful proofread with the help of a language
expert with all these issues in mind before resubmitting.