Abstract
BackgroundCore outcome set (COS) developers increasingly employ Delphi surveys to elicit stakeholders’ opinions of which outcomes to measure and report in trials of a particular condition or intervention. Research outside of Delphi surveys and COS development demonstrates that question order can affect response rates and lead to ‘context effects’, where prior questions determine an item’s meaning and influence responses. This study examined the impact of question order within a Delphi survey for a COS for oesophageal cancer surgery.MethodsA randomised controlled trial was nested within the Delphi survey. Patients and health professionals were randomised to receive a survey including clinical and patient-reported outcomes (PROs), where the PRO section appeared first or last. Participants rated (1–9) the importance of 68 items for inclusion in a COS (ratings 7–9 considered ‘essential’). Analyses considered the impact of question order on: (1) survey response rates; (2) participants’ responses; and (3) items retained at end of the survey.ResultsIn total, 116 patients and 71 professionals returned completed surveys. Question order did not affect response rates among patients, but fewer professionals responded when clinical items appeared first (difference = 31.3%, 95% confidence interval [CI] = 13.6–48.9%, P = 0.001). Question order led to different context effects within patients and professionals. While patients rated clinical items highly, irrespective of question order, more PROs were rated essential when appearing last rather than first (difference = 23.7%, 95% CI = 10.5–40.8%). Among professionals, the greatest impact was on clinical items; a higher percentage rated essential when appearing last (difference = 11.6%, 95% CI = 0.0–23.3%). An interaction between question order and the percentage of PRO/clinical items rated essential was observed for patients (P = 0.025) but not professionals (P = 0.357). Items retained for further consideration at the end of the survey were dependent on question order, with discordant items (retained by one question order group only) observed in patients (18/68 [26%]) and professionals (20/68 [29%]).ConclusionsIn the development of a COS, participants’ ratings of potential outcomes within a Delphi survey depend on the context (order) in which the outcomes are asked, consequently impacting on the final COS. Initial piloting is recommended with consideration of the randomisation of items in the survey to reduce potential bias.Trial registrationThe randomised controlled trial reported within this paper was nested within the development of a core outcome set to investigate processes in core outcome set development. Outcomes were not health-related and trial registration was not therefore applicable.
Highlights
Core outcome set (COS) developers increasingly employ Delphi surveys to elicit stakeholders’ opinions of which outcomes to measure and report in trials of a particular condition or intervention
While the Delphi process consisted of two survey rounds, this study focused on the impact of question order on round 1 responses
200 patients were invited to participate in the Delphi survey, of whom 130 (65%) provided consent and were allocated to and sent either a Patient-reported outcome (PRO) first or PRO last survey
Summary
Core outcome set (COS) developers increasingly employ Delphi surveys to elicit stakeholders’ opinions of which outcomes to measure and report in trials of a particular condition or intervention. Research outside of Delphi surveys and COS development demonstrates that question order can affect response rates and lead to ‘context effects’, where prior questions determine an item’s meaning and influence responses. A COS is an agreed minimum set of outcomes to be measured and reported in all trials of a particular condition or intervention [4]. Their development requires consensus methodology to establish outcomes considered most essential to patients and health professionals. Far less focus has been awarded to the actual design of the Delphi survey itself, which has been criticised as often being poorly formulated [17, 18]
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