ASK a medical patient how he feels about the internet and he may well wax lyrical. The web offers copious information about symptoms, diagnoses and treatments – empowering the individual to understand and discuss their illness. Ask a physician, however, and you may well be met with a resigned roll of the eyes. Even if a patient has tapped into a reliable source of information, their understanding of how it applies to them may be way off-base. One can easily imagine this divide widening thanks to the “self-tracking” movement, which stands to revolutionise doctor-patient relationships (see “Quantify thyself: Tracking your life from food to mood“). Monitoring your own vital signs promises significant benefits: continual health checks, advance warning of illness and personalised medicine. But here’s the rub. How should a doctor react to someone with no symptoms anxiously brandishing their own analysis of data from a consumer gadget? Equally, will patients eventually be compelled to understand or even conduct such analyses to secure proper treatment?