Review for 10.1186/s12876-021-01983-3 (2021)

Title: The analysis of multilevel factors affecting adenoma detection rates for colonoscopies:
A large-scale retrospective study
Version: 1 Date: 28 Dec 2020
Reviewer's report:
The manuscript „Comprehensive analysis of multilevel factors affecting adenoma detection
rates for colonoscopies: A large-scale retrospective study“ addresses a topic relevant to BMC
Gastroenterology
Overall it remains unclear what this study adds to the body of evidence. It is subject to a variety
of inaccuracies and lack of important information to assess its validity and to allow to put the
reported results into context. Validation of the results and assurance of accurate reporting by a
trained and experienced statistician is crucial.
Study population and colonoscopies
The indications for the colonoscopies (diagnostic or screening) are unclear. In case of diagnostic
colonoscopies what were the symptoms? Is this rather a diagnostic or a screening population?
Outcome
The primary outcome appears not to be the ADR but rather „adenoma detection (yes/no)“, since
logistic regression was used.
Please clarify how „adenoma“ was defined. How were findings of multiple adenomas dealt with?
Adding adenoma case numbers by histopathological features yields n=2380. How is the
difference to n=2180 adenoma cases explained?
How were cancers taken into account in the analysis? As adenomas? If yes, the endpoint  should
be defined differently (more accurately).
The target of screening are specifically also „advanced adenomas“. The prevalence of advanced
adenomas (according to a common classification) should be reported
Can factors determining the detection of advanced adenomas also be assessed? Such an analysis
would add more value to this manuscript.
Proceduralist factors
The variability/ distribution in the number of colonocopies per endoscopist should be reported;
ideally also findings by endoscopist
It seems hardly possible that reliable inferences can/ show me made on „proceduralist factors“
based on n=21 endoscopists.
Please clarify: proceduralist factors seem to be endoscopist factors. If yes, please use on term
only. e.g. „endoscopist-level factors“
Design/ statistical analysis
Please elaborate on variable selection for this analysis.
The „random effects multivariable model“ is most likely more accurately described as a “mixed-
effects model“ since fixed effects were considered too.
Critically discuss the potential impact of the „Table 2 fallacy“ (https://
pubmed.ncbi.nlm.nih.gov/23371353/)
Critically discuss potential overestimation of the OR due to violation of the „rare disease
assumption“
The authors state in a sub-heading that „univariate regression analysis“ was performed and report
the results of Table 1 and Figure 2 under this subheading. However, neither Table 1 nor Figure
2 present results from a regression analysis.
Please use „Multivariable regression analysis“ instead of „Multivariate regression analysis“ (see
e.g. https://www.karger.com/article/FullText/345491)
„Continuous variables with non-normal distribution were presented as median values (the lower
four quantiles, the upper four quantiles)“: this does not seem to have been applied.
The term „Continuous categorical variables“ is unclear.
The authors state: „Statistical analyses were performed by statisticians from the Clinical
Evaluation and Analysis Center of the First Affiliated Hospital of Zhejiang Chinese Medical
University“. This appears to be in contradiction to the statements made in the contributions of
each author, where the only one author with this affiliation is reported to only have supervised
the analysis.
Please indicate where a Fisher’s exact test was applied and reported.
P values are never „0.000“ (even though they are printed like this in SPSS outputs they should
not be in scientific articles)
Please state which statistical software was used at the end (not the beginning) of the statistical
analysis section, as it should be a mere technical detail, at least in standard analyses.
It is unclear how missing data were dealt with.
It is unclear whether a pre-specified protocol is available for this analysis. If yes, it should be
included as a supplement to allow an assessment of protocol deviations.
Was the analysis performed by a trained and experienced statistician? If not, was the analysis
validated by a trained statistician? In case validation was done by a trained statistician, how was
this validation done?
Other
The term „comprehensive“ with regards to this analysis seems inappropriate.
The analysis is based on an existing database. It is questionable that „data were retrospectively
collected“ is an appropriate description.
The conclusion is misleading: „The ADR is positively correlated with senior level endoscopists
and single examiner colonoscopies in patients under sedation.“ It can be understood as a
conditional statement, but interactions were not considered.
Introduction: An ADR of >=20% can not be „recommended“, it is more an aim or an indicators
of quality.
Introduction: I wondered why stool-based tests were not considered in the introduction in the
context of the contribution of screening to CRC incidence and mortality.
The term „older age brackets“ is unclear.
Please consider reporting according to a reporting guideline and/ or provide a checklist, e.g.
based on the STROBE recommendations.
Figure 1:
„Patients included“ is not patients included in the study. „Patients screened for eligibility“ (or
similar) may be more suitable
„Patient excluded (n=2707)“ should be „Patients exclude (n=2707“ in order to be consistent
„Colonoscopy cohort“: I would not consider this a cohort as this implies a follow up
Figure 2:
Endoscopist’s sex occurs twice
X-axis: „Colonoscopies (n)“ would be preferred to „Number“
Tables 1/2:
Please re-consider the use of „cohort“ for this sample
Please state p-value „<0.001“ instead of „0.000“
Consider use of „endoscopist-level“ instead of „proceduralist-level“
Two significant digits suffice for the OR estimates
Minor: Correct „Indictors“ to „Indicators"