Review for 10.1186/s12876-021-01677-w (2021)

Reviewer’s report
Title: 
Epidemiological Survey to Determine the Prevalence of
Cholecystolithiasis in Uyghur, Kazakh, and Han Ethnic Groups in the Xinjiang
Uyghur Autonomous Region of China- 
cross-sectional studies
Version: 
0 
Date: 
25 May 2020
Reviewer's report:
Review of the article:
BMC Gastroenterology: An Epidemiological Survey of Cholecystolithiasis in
Uyghur, Kazakh, and Han Ethnic Groups in the Xinjiang Uyghur Autonomous
Region of China
The current study is an epidemiological survey to investigate the prevalence and
risk factors of cholelithiasis in different Chinese ethnic groups and areas. A
random sample of 5454 residents was asked to fill out questionnaires and
underwent ultrasonography to assess gallstone status. The authors found out that
in Xinjiang the overall prevalence of gallstones was 15%. The prevalence was
higher with female sex, presence of fatty liver disease, higher age and higher
BMI. Furthermore, it was higher in southern Xinjiang and in the Uyghur ethnic
group.
Although the investigation of prevalence data about gallstones is not very new,
the study might add to the literature by providing data about a Chinese area with
higher prevalence. Furthermore, the use of ultrasonography to assess gallstone
status is a gold standard procedure which identifies symptomatic and
asymptomatic gallstones. 
The study is interesting, and the English is written in a well manner. However,
there are some major issues the authors should address and change to improve
the article. The main limitation is the Discussion and the incomplete presentation
of the findings. The authors should add a Table with characteristics of the study
population. Further, the discussion is not written in a standard way, it is lacking a
lot of references and seems to rely on a lot of speculation. Further, the authors
should be careful what they cite and how. Also, the method section needs some
extensions.
Please find my detailed comments below:
Abstract:
Minor point:
Conclusion: Are these different ethnic groups present in different parts of
Xinjiang (north/south)? Do both results say the same? Are there more Uyghurs
in the south?
Introduction:
Minor points:
Line 18: Maybe mention somehow how large this area is, e.g. the size or
population or both. You could also include a map.
Line 31 ff: I got a bit confused here. I wouldn't present findings (line 31) and
then the aim of the study (line 40ff). In my point of view, findings don't belong
in an introduction, I would delete the part (lines 31-39; lines do not really fit but
this might be an issue in the pdf conversion?)
Methods:
Major point:
See comment below to: 
Point 2.2.7 and Table 4
Minor points:
Page 5, line 50: please explain the word "hukou" for those who are not familiar 
Page 5, line 52: Are there any numbers available how many did not comply with
the ultrasonography or complete the questionnaire?
The questionnaire was own development. Was it validated? Can you look it up
somewhere? How long was it? How many questions where included? Maybe
add it in an online supplement? 
Page 6, line 5: What is meant with satisfactory cooperation? The completeness
of questions filled out? Please explain in more detail.
Page 6, line 15: self-reported weight was used? This might be worth a statement
in the discussion/limitations as well.
Either here, in the Introduction (or the Results, Table 1, see below comment)
should come a part explaining in more detail the area and groups who entered the
survey. Are there any specific differences between the groups? Why should one
have more gallstones than others? Which are in the south and which in the
north?
Results: 
Major points:
What I am missing is a real Table 1 with characteristics (from Table 4) of the
investigated population, across ethnic groups. Further, you might consider using
the same population for all endpoints or at least explain/note/mention the number
of missings in footnotes in the mentioned overview table of characteristics. 
Point 2.2.7 and Table 4:
Both, the text and the Table 4 should be clearer. Please summarize the findings
in the text. It should be clear which sex is at higher risk and what units were used
for age and BMI. How can I interpret the findings? What does the OR for age
mean? People from one age group to the other have a 5% higher risk/odds? Or is
it per year increase? Same for BMI? And smoking? Is it for smokers versus non-
smokers? Never smokers? Or with increase in cigarettes smoked? Please be
precise and also list all groupings and units in the methods under statistical
analysis.
Minor points:
If not required from the journal, I would report p values as e.g. <0.001 and not as
0.000.
Discussion:
Major points:
Please make yourself familiar of how to structure a discussion:
Line 59 ff: The difference in dietary habits of the Uyghurs is completely new to
me. This should be mentioned earlier in the results and Tables (again in the
Table 1 with characteristics). The first part of the discussion should only present
results of the study that have been explained already in the results section.
Instead, you explain new results (or is this from another study?) and you discuss
already other studies before finishing the summary of your own findings. 
Page 8, line 6: Please give a reference that dry air might increase the
development of gallstones. This is a risk factor I never heard of! The whole part
should be supported by references (e.g. page 8, line 2 "they rarely eat fresh fruits
and vegetables and do not exercise much" - where does that come from? The
current study? Other studies? The before mentioned reference? Then please cite
it again!)
Page 8, line 17: "The significant increase in the prevalence of cholecystolithiasis
among Uyghur women may be related to their increased body weight after
marriage" - again, where does this come from? The BMI you presented does not
say anything about marital status. If you have data about that, please add it to the
table of characteristics. If not, add a reference!
Please add references for all sentences that otherwise sound very speculative
(e.g. "may be related to the nomadic habits "…) 
In general, I don't think it is appropriate to question age, sex and BMI as risk
factors for gallstones. These factors are established since decades. If you want to
question them, then just for these specific types of ethnic groups (although I
don't know why these mechanisms should be different among them): 
For sex it would be ok, because you cited another study performed in those
groups that showed no strong gender effect. But please be careful: by just
reading the abstract of reference 12, I see that the authors actually did not say
that the prevalence is not related to sex. They state that gender was a risk factor
in the Uighur (which spelling is right? Theirs or yours?) patients! If you mention
the result from the Han then you should compare it with the Han and not with
other ethnic groups. Please be accurate when you cite other researchers' work!
Further, regarding age: "Previous studies have shown controversies over the age
factor" - again, this is not true! Of course, if you search for it, you might find
some studies, but regarding the whole body of evidence age is a very much
established factor. You present it as if this is a new finding. You can say so, if
you are just talking about the investigated ethnic groups. If these are so special
that they show different associations?! However, the reference you refer to here
(14) is a study in patients with preconditions. You can't compare those to your
population or justify the questioning of well-established gallstone risk factors.
Page 8, line 29: It looks as if you consider people older than 30 as elderly? Why
did you choose this cut-point? 60 years would make more sense. 
Page 8, line 42: again, is there a reference where the climate differences etc. are
explained? Or at least a webpage with weather statistics or something similar?
In general, regarding BMI groups: I know the grouping in Asia is different than
the European or American ones, but is a BMI of 25 really considered obese? If
not, I would recommend using official groups of BMI according to the WHO or
some Asian official organisations. If that is already the case, please cite them. 
Page 9, line 28: Actually, the prevalence of gallstones in the Kazakhs was not
really low, it was just surprisingly low in women (or high in men), which should
be discussed here.
Page 9, line 31 "In Korea [24], the prevalence of cholecystolithiasis among
immigrants in Jeju
Island is relatively high, possibly because most of the Han population from
Xinjiang migrated
there." - sounds very speculative. Is this what the authors of reference 24 say or
your opinion? You can't draw strong conclusions like that. This needs a reference
or should be said in a less strong way.
Page 9, line 36: Although this is not my profession, I pretty much believe that
the hormone secretion/circadian clock will adjust after a while when people
move to other countries. If this is not the case, which I very much doubt, this
should be supported by another trustful reference. 
Page 9, line 42: I don't see the connection with alcohol in your study! You never
mentioned the alcohol drinking habits of your study population. If you have this
information, it would be wise to add it to the suggested Table 1. You can't draw
conclusions about alcohol drinking and gallstones just from prevalence data of
fatty liver disease, if this was the case here. These are two different things!
Page 10, line 20: "Finally, many factors that affect cholecystolithiasis were not
included, such as the composition of drinking water, the type of diet, and other
diseases" 
- Please be more specific and add references - what in drinking water
has an influence on gallstone formation? What other diseases then diabetes and
fatty liver disease are meant?
The summary following page 10, line 24 should come first in the discussion. For
a conclusion, results are a bit too detailed and repeated at this point.
What I think is missing, is a discussion on the basis of the associations between
the different factors, which again needs a Table 1 with characteristics. The
reasons for the differences between the groups should be more explained from
your results. Are the Uyghurs just older, more women, do they have a higher
BMI, and do they live in the south? Or are the findings completely
unexplainable? This is all not clear to me!
Tables and Figures:
Major points:
Table 1: add a Table 1 with characteristics as explained
Table 4: As mentioned, please include footnotes with explanations and add units
after the investigated factors. Further, in my opinion the Table would be easier to
interpret if only OR and 95%CIs would be presented. There is no need to show
degrees of freedom or Wald values.
Minor points:
Tables: 
- same comment here to the presentation of p-values
- explain why total numbers differ from table to table (see Results major point)
Figure 2 has a typo ("without")
Table 3: just to stick with one standard I would delete "in Xinjiang" from the
title like in the other tables
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.
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 statistics 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.
Not relevant to this manuscript
Quality of written English
Please indicate the quality of language in the manuscript:
Acceptable
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