Impact of "Spin" on the Interpretation of Results of Randomized Trials in the Field of Cancer
The investigators planned a RCT in which the unit of randomization is the abstract. The
planning, implementation, analysis and writing of this study followed the CONSORT
Two types of abstracts were evaluated: abstracts with and without "spin". Randomization
The randomization list was established in blocks of 30. So, each participant could evaluate
1 abstract with spin or 1 abstract with no spin.
The list and the block size were not disclosed to investigators. Allocation concealment was
obtained by use of a computerized randomization system.
If a participant logged on the system but did not evaluate any abstract, the assessments
were excluded and the abstracts were automatically allocated to the next participant.
Evaluators participating in this study were as follows:
1. The "corresponding authors" of published RCTs in the field of cancer. The investigators
systematically searched Medline via PubMed to identify all publications of RCTs in 2012
and if needed 2011, 2010. The investigators collected all e-mails of "corresponding
authors" of these items.
2. Experts of a French national grant in the field of cancer All potential participants
were invited by e-mail to participate in a study on the interpretation of results of
abstracts of clinical trials. If they agreed to participate, they used an Internet link
that gave them access to abstracts to assess.
3. Investigators of trials registered in clinicaltrials.gov
Intervention and comparators
Selection of abstracts with spin We selected from previous work and personnel
collection13-16, 30 abstracts of 2 parallel arms negative RCTs (ie, non-statistically
significant primary outcome) evaluating treatment in the field of cancer and having spin in
the abstract conclusion according to a classification developed previously13. We excluded
abstract with very unusual type of spin such as a focus on another study objective, with
spin related only to safety, or study comparing the same treatment but with different dosage
or different mode of administration or different duration of treatment. We also excluded
abstract of RCTs with small sample size (<100). Abstract were numbered from 1 to 30 and were
classified in two categories: 10 abstracts (numbers 11/12/14/16/20/22/24/27/28/30) with high
level of spin (i.e., no acknowledgment of the non statistically significant primary outcome
in the conclusion) and 20 with low level of spin.
Development of abstracts without spin The abstracts with spin were systematically rewritten
without spin. One researcher rewrote each abstract according to specific guidelines
described in the box. All abstracts had the same number of words +/-25. All abstracts
without spin were evaluated independently by another researcher any disagreement were
discussed and the abstract was modified according to the consensus reached.
Thus, for each study, the investigators had 2 versions of the abstract: 1 with spin and 1
Abstracts with and without spin were presented in the format of the original abstract with
the same typography. The names of authors, references, journal name, registration number,
trial name or acronym, and article title were deleted, and the treatment names and
description were systematically masked with generic terms (e.g., treatment A and comparator
B). If needed some information that could help identifying the treatment were deleted.
Primary outcome The primary endpoint was participants' interpretation of the abstracts. All
study participants evaluated each abstract. They answered the following question on a
numerical scale graded from 0 (not at all likely) to 10 (very likely)
• Based on this abstract, do you think treatment A would be beneficial to patients? (answer:
numerical scale from 0-10)
The secondary endpoints were the assessment of the study quality, the study importance, the
interest in reading the full text and the probability of being published. For each abstract,
the participants answered the following:
- Rate the overall rigor of the study methodology? (scale 0-10)
- Rate the importance of the study (scale 0-10)
- Are you interested in reading the full article for the study described in this
abstract? (scale 0-10)
- Do you think it would be interesting to run another trial evaluating this treatment?
The primary endpoint is the interpretation of the abstract by participants. This outcome is
very subjective. A recent study has shown that lack of blinding is responsible for an
overestimation of treatment effect in randomized trials with subjective primary endpoints17.
To minimize bias, the investigators proposed to have participants blinded to the study
hypothesis. All participants were informed that they were participating in a survey on the
interpretation of abstracts of clinical trials. They were not informed of the objectives and
assumptions of the study before the end of the study when reporting the results.
Other data collected The investigators also collected the changes to abstracts in terms of
words deleted and words added to each abstract.
Each participant will read 1 abstract with or 1 abstract without spin. A sample of 266
assessments of abstracts is needed to show an effect size of 0.4 with primary outcome
assuming a mean difference of 1 point and a common standard deviation based on a pilot study
of 2.5 with a power of 90% and an alpha risk equal to 5%. Thirty abstracts with spin and 30
abstracts without spin are available. Theoretically, each abstract must be read the same
number of times according to randomization group. Considering all these elements, it will be
necessary to include 300 participants (150 in each arm). Each abstract will be read 5 times
in each group (abstract with low level of spin will be read 200 times (100 in each group)
and abstract with high level of spin will be read 100 times (50 in each group)).
Statistical analysis will be undertaken independently and blindly with use of SAS v9.3 by a
statistician of the Centre for Clinical Epidemiology. A statistical analytic plan will be
developed and validated before searching the database. The statistical analysis plan will be
revised during the study to take into account any amendments to the protocol or any other
change having an impact on the statistical analysis originally planned. All versions will be
kept on file for review. A T test will be used for analysis of primary and secondary
outcomes. This statistical plan can be modified according to available data. For instance,
if the number of readings for a particular vignette is unbalanced in groups, a multi-level
model (a mixed model for clustered data) will be used to compare adjusted means for the
primary outcome measures between the 2 arms. This means that statistical analysis will be
adjusted for unbalanced repartition of abstracts in each group. The same model will be
applied to secondary outcomes and to the subgroup abstracts with high level of spin.
A secondary analysis will compare the ICC between readers of abstracts with spin and
abstracts without spin by computing the 95% confidence interval of the difference between
ICCs (by a bootstrap method).
Allocation: Randomized, Intervention Model: Parallel Assignment, Masking: Single Blind (Subject)
interpretation of the abstracts
The primary endpoint was the interpretation of abstract results by the participants. All readers participating in the study evaluated the abstracts of randomized trials and answered the following questions: based on this abstract, do you think treatment A would be beneficial to patients? (answer: numerical scale from 0-10)
isabelle BOUTRON, PhD
Assistance Publique - Hôpitaux de Paris
France: Ministry of Health