Review for 10.1186/s12876-021-01879-2 (2021)

Reviewer’s report
Title: 
Pain and psyche in a patient with irritable bowel syndrome—chicken or
egg? A time series case report
Version: 
0 
Date: 
04 Jan 2021
Reviewer's report:
The paper by Engel and colleagues provides an interesting and potentially useful
insight into the relationship between psychological traits and gastrointestinal
symptoms in an individual diagnosed with Rome irritable bowel syndrome
(IBS). The authors take a time-series approach to understanding the bi-
directional relationships between psychological factors and symptom experience,
concluding that symptoms precede psychological events more so than the other
way around. Their findings stand in some contrast to the usual bi-directional
view of brain-gut interactions.
The authors conclusions are generally well supported, however there are a few
points that I believe need clarification.
1. An intensive study of a single individual yields insights at a very detailed level
that are difficult to achieve when studying groups, and the authors allude to this
when discussing previous work that revolved around averages. I agree with the
benefits of the approach they have taken. However there is also a price to pay in
that generalising from one patient to the population of patients does not
automatically follow, and this could potentially explain some of the
discrepancies they report between this work and previous studies. I expect the
authors understand this but I think it needs to be drawn out more explicitly in
both the Introduction and Discussion.
2. Are somatic symptoms in Table 4 an average of abdominal pain and daily
impairment in Table 3? I was not clear on exactly how SS is measured.
3. Another point that I was not clear on is whether all combinations of
psychological variables predicting symptom level and vice versa were
calculated, and only the statistically significant findings reported in Table 4. I
think this is what happened but clarification in the text would be useful.
4. The column heading "h=10" in Table 4 is not explained.
5. Statistical terminology needs to be more carefully defined, for example the
term "instantaneous correlation" presumably means correlation between SS and
psych at a given time, but the reader should not have to guess. Similarly, line
165 on page 6 lists a number of statistical analyses conducted but not what they
represent or how they contribute to answering the study's research questions. I
think a more careful explanation and possibly being more selective about which
statistical analyses are reported would help this paper. The authors' conclusions
hang on this unusual, for the field, statistical approach and hence a clear and
specific explanation is important.
6. This is a specific example of my previous point but is absolutely central to the
paper. On page 6, starting line 171, the concept of Granger-causality is explained
but only in one sentence. This seems to me to be the single most important
concept in this work and needs to be teased out further such that the clinical
interpretation is clear to a non-statistical reader. Without understanding what
Granger-causality means in a tangible sense I do not see how the reader can
judge whether they agree with the interpretation provided.
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Is the study design appropriate to answer the research question (including the use
of appropriate controls), and are the conclusions supported by the evidence
presented?
No
Are the methods sufficiently described to allow the study to be repeated?
Yes
Is the use of statistics and treatment of uncertainties appropriate?
Yes
Is the presentation of the work clear?
Yes
Are the images in this manuscript (including electrophoretic gels and blots) free
from apparent manipulation?
Yes