Background/aims: The analyses of randomised controlled trials with missing data typically assume that, after conditioning
on the observed data, the probability of missing data does not depend on the patient’s outcome, and so the data are ‘missing
at random’ . This assumption is usually implausible, for example, because patients in relatively poor health may be more likely
to drop out. Methodological guidelines recommend that trials require sensitivity analysis, which is best informed by elicited
expert opinion, to assess whether conclusions are robust to alternative assumptions about the missing data. A major barrier
to implementing these methods in practice is the lack of relevant practical tools for eliciting expert opinion. We develop a
new practical tool for eliciting expert opinion and demonstrate its use for randomised controlled trials with missing data.
Methods: We develop and illustrate our approach for eliciting expert opinion with the IMPROVE trial (ISRCTN
48334791), an ongoing multi-centre randomised controlled trial which compares an emergency endovascular strategy
versus open repair for patients with ruptured abdominal aortic aneurysm. In the IMPROVE trial at 3 months post-randomisation,
21% of surviving patients did not complete health-related quality of life questionnaires (assessed by EQ-5D-3L).
We address this problem by developing a web-based tool that provides a practical approach for eliciting expert opinion
about quality of life differences between patients with missing versus complete data. We show how this expert opinion
can define informative priors within a fully Bayesian framework to perform sensitivity analyses that allow the missing data
to depend upon unobserved patient characteristics.
Results: A total of 26 experts, of 46 asked to participate, completed the elicitation exercise. The elicited quality of life
scores were lower on average for the patients with missing versus complete data, but there was considerable uncertainty
in these elicited values. The missing at random analysis found that patients randomised to the emergency endovascular
strategy versus open repair had higher average (95% credible interval) quality of life scores of 0.062 (20.005 to
0.130). Our sensitivity analysis that used the elicited expert information as pooled priors found that the gain in average
quality of life for the emergency endovascular strategy versus open repair was 0.076 (20.054 to 0.198).
Conclusion: We provide and exemplify a practical tool for eliciting the expert opinion required by recommended
approaches to the sensitivity analyses of randomised controlled trials. We show how this approach allows the trial analysis
to fully recognise the uncertainty that arises from making alternative, plausible assumptions about the reasons for
missing data. This tool can be widely used in the design, analysis and interpretation of future trials, and to facilitate this,
materials are available for download.