Intended for healthcare professionals

CCBYNC Open access
Research

Soluble or insoluble fibre in irritable bowel syndrome in primary care? Randomised placebo controlled trial

BMJ 2009; 339 doi: https://doi.org/10.1136/bmj.b3154 (Published 27 August 2009) Cite this as: BMJ 2009;339:b3154

Randomisation

Bijkerk et al examined the effectiveness of increasing the dietary
content of soluble fibre (psyllium) or insoluble fibre (bran) in patients
with irritable bowel syndrome (1). Participants were randomised to 12
weeks of treatment with 10g psyllium, 10g bran or 10g placebo (rice
flour). When reading this article, it is not entirely clear how the
randomisation sequence was generated. At first reading it seems that the
randomisation sequence was generated using blocked randomisation with a
block size of 6 and was concealed using sealed non-opaque envelopes. Yet
this would imply that there should only be a difference of, at most, 2
patients between the treatment groups. However, there was a disparity of
12, 8 and 4. Consequently the authors cannot have used fixed block sizes
as suggested in their paper. Can the investigators describe their
randomisation process in more detail in order to explain the unexpected
discrepancy in group sizes?

David J Torgerson, PhD, Director, York Trials Unit

Catherine E Hewitt, PhD, Research Fellow, York Trials Unit

(1) Bijkerk CJ, de Wit NJ, Muris JWM, Whorwell PJ, Knottnerus JA,
Hoes AW. Soluble or insoluble fibre in irritable bowel syndrome in
primary care? Randomised placebo controlled trial. BMJ 2009; 339: b3154
doi:10.1136/bmj.b3154

Competing interests:
None declared

Competing interests: No competing interests

04 September 2009
David J Torgerson
Professor
Catherine E Hewitt
York Trials Unit