Should researchers standardise usual care arms in randomised controlled trials?

Problem

Many primary care trials evaluate new or modified treatments against usual care. To strengthen a trial’s external validity, this comparator should resemble everyday clinical practice. However, usual care for the same condition can differ across trial sites, over time, and between patients and practitioners. This heterogeneity can make interpretation and translation of findings difficult and can raise scientific and ethical issues. It may be appropriate, therefore, to standardise what usual care entails when using it as a comparator arm, although doing so may compromise a trial’s external validity if the care provided differs from what is normally delivered. Currently there is no guidance or overview detailing how researchers designing trials should decide the content of usual care comparators. We conducted a methodology review to summarise current thinking about what should inform this decision.

Approach

MEDLINE, EMBASE, CINAHL and PsycINFO were searched from inception to January 2022. Reference lists and forward citation searches of included studies were screened to identify additional relevant studies. 1930 records were identified and after de-duplication, 1611 titles and abstracts were screened. 112 were included for full-text screening and 16 were included in the review. Data were analysed using a narrative synthesis approach.

Findings

The aims of the trial, the heterogeneity of usual care, the vulnerability of the patient population, the effectiveness of existing care, the existence of clinical guidelines, the views of stakeholders, the requirements of robust ethical research, and the extent to which the intervention being evaluated needed to be modified for implementation in real-world settings, were identified as factors that should inform the content of a usual care arm. In terms of recommended actions that should be undertaken when making this decision, these included establishing what usual care is at the different study sites, discussing alternative comparators with policy makers and providers, and establishing criteria to review possible alternatives.

Consequences

Previous research has outlined what factors should inform the decision about whether to standardise usual care in a trial. It has also defined what actions should be undertaken during this process. However, this is a complex decision-making process and little attention has been given to how researchers can manage tensions that occur when trying to address competing priorities. Unless greater attention is given to the characterisation of usual care arms, primary care trials will remain hindered in the extent to which they can provide strong evidence to inform policy and practice