Abstract
BackgroundTrials using inadequate levels of blinding may report larger effect sizes than blinded studies. It has been suggested that blinded outcome assessment in open trials may in some cases be undertaken by assessments of photographs. The aim of this paper is to explore the effect of using different methods to assess the primary outcome in the EVerT (Effective Verruca Treatments) trial. It also aims to give an overview of the experiences of using digital photographs within the trial.MethodsWe undertook a secondary analysis to explore the effect of using three different methods to assess the primary outcome in the EVerT trial: assessment of digital photographs by blinded healthcare professionals; blinded healthcare professional assessment at the recruiting site and patient self-report. The verruca clearance rates were calculated using the three different methods of assessment. A Cohen’s kappa measure of inter-rater agreement was used to assess the agreement between the methods. We also investigated the experiences of healthcare professionals using digital photographs within the trial.ResultsDigital photographs for 189 out of 240 (79 %) patients in the trial were received for outcome assessment. Of the 189 photographs, 30 (16 %) were uninterpretable. The overall verruca clearance rates were 21 % (43/202,) using the unblinded patient self-reported outcome, 6 % (9/159,) using blinded assessment of digital photographs and 14 % (30/210,) using blinded outcome assessment at the site.ConclusionsDespite differences in the clearance rates found using different methods of outcome assessment, this did not change the original conclusion of the trial, that there is no evidence of a difference in effectiveness between cryotherapy and salicylic acid. Future trials using digital photographs should consider individual training needs at sites and have a backup method of assessment agreed a priori.Trial registrationISRCTN Registry ISRCTN18994246
Highlights
Trials using inadequate levels of blinding may report larger effect sizes than blinded studies
Secondary analysis to explore the effect of using different methods of outcome assessment Figure 1 shows the flow of patients through the trial
Digital photographs were taken at the 12 week outcome assessment point and the coordinating centre received photographs for 189/240 (79 %) patients
Summary
Trials using inadequate levels of blinding may report larger effect sizes than blinded studies. For outcome assessors there is the potential to report more favourable outcomes for those in the novel intervention group if they believe it to be a superior treatment This is more likely to be an issue where more subjective outcomes such as pain scores are being assessed rather than objective outcomes such as death. There are several advantages to using digital photographs for outcome assessment It eliminates the verbal and non-verbal clues about group allocation and allows the same assessors to evaluate the outcome for all participants in a study. It assists with demonstrating the transparency of the data. Additional time is required to handle the photographs at the study coordinating centre
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