Background

Because pragmatic trials are performed to determine if an intervention can improve current practice, they often have a control group receiving ‘usual care’. The behaviour of caregivers and patients in this control group should be influenced by the actions of researchers as little as possible. Guidelines for describing the composition and management of a usual care control group are lacking.

Aim

To explore the variety of approaches to the usual care concept in pragmatic trials, and evaluate the influence of the study design on the behaviour of caregivers and patients in a usual care control group.

Design of study

Review of 73 pragmatic trials in primary care with a usual care control group published between January 2005 and December 2009 in the British Medical Journal, the British Journal of General Practice, and Family Practice. Outcome measures were: description of the factors influencing caregiver and patients in a usual care control group related to an individual randomised design versus cluster randomisation.

Results

In total, 38 individually randomised trials and 35 cluster randomised trials were included. In most trials, caregivers had the freedom to treat control patients according to their own insight; in two studies, treatment options were restricted. Although possible influences on the behaviour of control caregivers and control patients were more often identified in individually randomised trials, these influences were also present in cluster randomised trials. The description of instructions and information provided to the control group was often insufficient, which made evaluation of the trials difficult.

Conclusion

Researchers in primary care medicine should carefully consider the design of a usual care control group, especially with regard to minimising the risk of study-induced behavioural change. It is recommended that an adequate description of the information is provided to control caregivers and control patients. A proposal is made for an extension to the CONSORT statement that requires authors to specify details of the usual care control group.