Review for 10.1186/1471-230X-9-85 (2009)

Reviewer's report
Title:A prospective, randomized, double-blind, placebo-controlled parallel-group
dual site trial to evaluate the effects of Gas Defense on intestinal gas symptoms
in otherwise healthy adults
Version: 2Date:10 June 2009
Reviewer: Carl J Lombard
Reviewer's report:
The authors would do well in using the CONSORT statement to evaluate the
reporting of the different elements of their study. For example randomisation. In
the title of the document there is mention of a two (dual) sites - this is never
addressed in the document but this raises the question about the randomisation -
was it done by site? If not how was the randomisation done across sites? How
was the active and placebo treatments prepared provide for the randomisation?
Who was responsible for the randomization and how was blinding ensure in the
preparation of the treatments?
How was the study products dispensed and how many capsules were provided?
What was the compliance and was this assessed? Did the participanst keep to
the directive of taken the capsule at the same time each day?
Who was responsible for the conduct/ completion of the quesionnaires? What is
meant by administered? Was it self administered questionnaires? Were all the
interview doen by the same interviewer / administrator in each site? Were all the
interviews done at exactly 14 and 29 days? Were the subjects compensated for
their participation? I ma not familiar with the different instruments and therefor
have not feel what time horizon the scales covers - is it the current moment,
yesterday, past week etc? What does a abdominal pain score of 3.17 mean at
baseline. Is this a high score, a very severe state?
Statistical comments
There is no motivation provide for the choice of an .8-sigma effect size. It seems
as if the sample size was fixed and then an effect size was looked at. Why not at
.75 sigma effect size?
Comparison of the baseline characteristics (Table 1) using a significance test is
not advised. Assuming your randomisation was flawless the observed differences
is purely due to chance. It is interesting to note that the baseline comparison for
the study outcomes was not statitically compared - table 3- 5 which is fine.
If randomisation was stratified by site this design factor has to be taken into
account in the analysis of the study outcomes. For the study outcomes a ancova
is done using the 29 day score only. The study in fact as two post randomisation
observations (at 14 days and at 29 days) and a repeated measures ANCOVA
with time, treatment and baseline measurement will have more power. Looking at
Tables 3-5 there is some evidence of an intervention effect at 14 days allready
and adding this will improve the power of the analysis. You went to the trouble of
collecting the information at day 14 and this information should be utilized in the
evaluation of the intervention.
Reporting within group changes and then comparing them verbally between the
groups is not a sound practice. Keep it desriptive and if you want to report on the
changes over time between the two groups do a formal test with a time*
treatment interaction in a regression model that takes the into account the
repeated measurements within each participant.
Level of interest: An article whose findings are important to those with closely
related research interests
Quality of written English: Acceptable
Statistical review: Yes, and I have assessed the statistics in my report.
Declaration of competing interests:
'I declare that I have no competing interests'