Acute cough is the most common symptom managed by healthcare services, and it is associated with large personal, societal, and healthcare costs. In the linked randomised cluster controlled trial (doi:10.1136/bmj.b1374), Cals and colleagues assess the effects of communication skills training and the use of C reactive protein (CRP) testing on the prescription of antibiotics to patients with lower respiratory tract infection in primary care.1

The participants were older than 18 years, they had an acute (no more than four weeks’ duration) cough considered by the general practitioner to be caused by lower respiratory tract infection, and they had at least one chest symptom or sign and at least one systemic symptom or sign.2 The investigators tried to recruit patients with what most clinicians would recognise as acute bronchitis, influenza, acute exacerbations of asthma, and acute exacerbations of chronic pulmonary obstructive disease. They excluded patients who currently or recently needed antibiotics or hospital admission.

The trial used a factorial design, and the units of randomisation were individual general practitioners’ practices. Although cluster randomisation aims to prevent the control group from also receiving a group level intervention, such as communication skills training, it is not the preferred design for individual level interventions, …