Many trials in primary care require a pragmatic design. In contrast to explanatory trials, which are performed under ideal and controlled conditions, pragmatic trials measure the effect of an intervention in real clinical practice. Because pragmatic trials are performed to determine whether the intervention can improve current practice, they often have a ‘usual care’ control group. The care received by this control group is supposed to reflect the care as usually received by patients in daily practice.1
The design of a trial with a usual care control group requires specific attention (Box 1
). The main difficulty is to ensure that this control group receives genuine usual care as supplied in everyday practice.2
However, various actions by the researchers may influence the behaviour of caregivers and patients. For example, behavioural change of control caregivers may be induced when they are informed about the issues under study, or because of a learning effect when they have to provide usual care to one patient and an intervention to another. Behavioural change of control patients may be induced when they are briefed about the trial and asked to give informed consent, or when they are asked to complete questionnaires and undergo examinations, drawing their attention to their condition and possible interventions. These actions may change their help-seeking behaviour or influence their complaints. This, in turn, may affect the outcome and the interpretation of the trial. Consequently, researchers have to think carefully about the influence of the study information and the intervention on the control group and on how to minimise this effect.
Box 1. Example of dilemmas faced by the present authors when designing a pragmatic trial with a usual care control group.
Guidelines give clear advice about prophylactic medication for migraine patients with frequent headaches. However, GPs do not often prescribe this medication. This study's authors decided to perform a randomised clinical trial to establish the advantages of a new intervention aimed at improving migraine treatment by GPs. Most likely this will be a pragmatic trial with one group of GPs applying the intervention and another group continuing their normal way of working (‘usual care’). For an optimal comparison it is preferable if control patients and control physicians are unaware of the study. However, patients have to be invited to participate, need to provide informed consent, and have to complete questionnaires to measure the outcome. Furthermore, control physicians have to be informed and agree to participate. Therefore, physicians and patients will be aware of the study and this could change or adapt their normal behaviour. For example, physicians could start studying the available guidelines on migraine and subsequently re-evaluate the therapy options for their migraine patients; patients might decide to visit their physician after reading the information and filling in the questionnaire; and, just after the study has started, an update of the national headache guideline might be sent to all GPs. For both the researcher and the reader it is difficult to estimate the impact of all these possible influences.
Researchers have different opinions about the meaning of the term ‘usual care’ and, consequently, apply different methods when designing and reporting a trial with a usual care control group. Guidelines on the reporting of trials are available to researchers in the CONSORT statement, including its extension to cluster randomised trials, and its recently published extension to pragmatic trials.3–5
However, these guidelines do not cover the specific requirements for describing the composition and management of a usual care control group. Two recent reviews on the validity of pragmatic cluster randomised trials focused on other issues, that is, mainly on the risk of selection bias. Until now, the risk of behavioural change of caregivers and patients in trials with a usual care group has been discussed only marginally.6,7
A recent review on low back pain reported a poor description of the usual care control arm in 26 of 33 reviewed studies.8,9
To gain insight into the variety of approaches to the usual care concept in primary care research, this study explored a cohort of pragmatic trials with a usual care control group, reporting for individually randomised and cluster-randomised studies separately. Furthermore, it examined the possible influences of the study information and awareness of the intervention on the behaviour of control caregivers and control patients. This overview shows the problems researchers face when designing pragmatic trials with a usual care control group.