Does declaration of competing interests affect readers' perceptions? A randomised trial

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Abstract
We randomly selected 300 BMJ readers from the BMA's membership database, which contains individual reader characteristics. All readers were sent a short report indicating that the impact of pain from herpes zoster on patients' daily functioning may be substantial.5 Readers in group 1 were sent a version of this paper with different named authors to the original and with a declaration that they were employees of a fictitious company and potentially held stock options in the company. Readers in group 2 were sent a version of the same paper with the same named authors as in group 1 but with a statement that these authors were from an ambulatory care centre and had no competing interest. Readers were asked to rate the study in terms of interest, importance, relevance, validity, and believability on 5 point Likert scales (1=extremely uninteresting to 5=extremely interesting). We estimated that 86 readers were needed in each group to achieve a power of 90% to detect a difference in scores between the groups of 0.5 units on the 5 point scale. We used a simple two sample t test with the conventional 5% significance level and assumed a common standard deviation of 1.0.