Web-based IMEs provide the potential for better clinical simulations, which have the potential to lead to better interventions. The current proposal will run a full, web-based IME involving 250 GPs that will advance the methodology of IMEs by directly comparing results with an earlier paper-based IME. Moreover, the web-based IME will evaluate an intervention that can be put into a full-scale trial that aims to reduce antibiotic prescribing in primary care. Reducing inappropriate prescribing of antibiotics in general practice is a national priority; indeed, antibiotic use is increasing in the UK and Scotland's prescribing is second highest amongst UK administrations. More effective behaviour change interventions are needed and this proposal will develop one such intervention and a system to model and test future interventions. This system will be applicable to any situation in the NHS where behaviour needs to be modified, including interventions aimed directly at the public.