The use of masking procedures.
Kjaergard and Als-Nielsen [ref 1] describe an apparent bias in papers
published in the BMJ, such that authors’ conclusions seem more positive
towards the experimental intervention in trials funded solely by for
In such a study, which examines the subtle influences of bias on
human perception and behavior, it is necessary for the investigators to
take very rigorous precautions to avoid introducing the same kind of bias
into their own investigation. Although there seems to be good agreement
between raters’ assessment of authors’ conclusions on a six point scale,
there is still enough variation and subjectivity in this assessment for
bias to be a serious concern.
At the very least, assessments of authors’ conclusions must be made
without any knowledge of the source of funding and assessment of source of
funding must be made without any knowledge of the authors’ conclusions.
The procedures for ‘masking’ or ‘blinding’ used in this investigation
do not meet this standard. One of the investigators assessed both source
of funding and authors’ conclusions without any masking. The second
investigator assessed authors’ conclusions without knowledge of the source
of funding. Unfortunately, the two investigators then colluded together to
agree a final score for the author’s conclusions, so any benefit from the
masking would have been diminished or lost. Even if they had not colluded,
and the un-blinded investigator’s assessment of authors’ conclusions had
not been used, there is still the possibility of bias because the only
assessment of source of funding was made with knowledge of the author’s
It would be very interesting if Kjaergard and Als-Nielsen were to
repeat this study using rigorous masking procedures to see if they still
get the same result.
1 Kjaergard L L and Als-Nielsen B. Association between competing
interests and authors’ conclusions: epidemiological study of randomised
clinical trials reported in the BMJ. BMJ 2002; 325: 249 (3 August)
Competing interests: No competing interests