Review for 10.1186/s12876-023-02796-2 (2023)

Title: Risk factors for inadequate bowel preparation before colonoscopy: a retrospective cohort
study
Version: 8 Date: 07 Mar 2023
Reviewer's report:
Your study is almost ready to publish and the first 2 comments are minor.
I remain concerned your latest revision continues not to address my concern regarding the
variables you looked at with the multi-variable analysis.
Abstract:
Methods: In this retrospective study, patients who underwent colonoscopy in 2018 and received
3 L of Polyethylene Glycol Electrolytes powder were included. They were instructed to drink
1.5 l the night before the colonoscopy and 1.5 l -6 hours before the procedure given in doses of
250 ml every 10 minutes with 30 ml of simethicone given 4-6 hours before the colonoscopy
it should be 4-6 hours before the procedure (not 1-6) - this was my typo but you need to catch
it since it is your proticol.
Methods:
The overall score for the BBPS was the sum from all three segments, ranging from 0 (completely
unprepared) to 9 (perfect).
Perfect should be changed to excellent. The prep is not perfect since cleaning maneuvers can
be performed and still get a 9.
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This is the FORTH time I bring up this point since it is important:
15. My questions
from last time> Was season the primary endpoint of the study when it was designed?Your
Response 1: Thank you for your helpful comment. As you said, we found that
season may be an influencing factor of poor intestinal preparation through clinical
observation, so we took season as one of the variables in our data statistics.
MyQuestion: The study endpoints are really your multi-variable analysis of risk factors
for inadequate preparations as defined by BBPS segments all >=2. I think you need to list the
variables you planned to analyze when the study was designed and if that
included season. Was season something you added after you had the data and not edit
was statistically significant? Most studies describe a primary endpoint and secondary endpoints
before the study is undertaken. For example, if you have 20 endpoints you evaluate, then, just
by chance alone, one is likely to be positive at a 0.05 level. It
needs to be clearly stated in the design of the study what
Response 2: Thank you for your careful advice. During the design phase of our study, the initial
consideration was to find that many patients underwent colonoscopy had inadequate bowel
preparation quality even after taking intestinal cleansers as required. Therefore, our
primary endpoint in designing this study was to explore risk factors for inadequate bowel
preparation quality, and season was included as only one factor that might
affect bowel preparation quality. In addition, patients' basic information (age, sex),
chief complaint, time for colonoscopy, colonoscopic findings and hospitalization status were
also included as potential factors.
Response: Thank you for your suggestion. The endpoints of a clinical study are generally the
measures that evaluate the efficacy of the clinical study. There is only one primary endpoint,
and there can be multiple secondary endpoints, but all of these indicators must have recognized
judgment criteria that can directly determine the efficacy of the study. For example, in the study
of risk factors affecting the survival of
oncology patients, the survival rate is its endpoint indicator. In this study, we mainly explored
the risk factors affecting bowel cleanliness, therefore, our primary endpoint
indicator was bowel cleanliness as judged by BBPS, which was also mentioned in previous
studies (Endoscopy 51(7):628-636). The main factors we considered for
inclusion in the initial study design were gender, age, chief complaint, time of
colonoscopy, colonoscopy findings, season, and whether hospitalized or not. Season was an
influential factor included in our study, and the finding that season was an influence on bowel
cleanliness was the more important finding of this study, and not the season as an outcome
indicator.
For the FORTH time, I will discuss this issue.
The primary endpoints of your study are the variables that you look at in the multi-variable
analysis. The BBPS score is not the primary endpoint as it would be if you were comparing 2
different bowel preparation regimens.
In the Methods section you MUST include:
1) if the endpoints were selected in the design phase of your study before you analyzed the
retrospective data.  Did you evaluate any other variables that you did not include in the paper?
2) Was season the primary variable you wanted to evaluate when designing the study?  OR --
Was it the most interesting finding of your study and so you emphasized it in the paper? You
need to describe this in the methods section so the significance of your findings can be better
understood.
3) List ALL the variables that you prospectively planned to evaluate when looking back on your
existing cleanliness data.
What if you looked at 25 variables and only reported 5? The significance of the findings would be
much lower since by chance alone you might find 1 or 2 independent risk factors for inadequate
bowel preparation at the 0.05 level.