Diagnosis is one of the primary tasks of the Primary Care Physician or General Practitioner (GP), diagnostic error is also the single greatest reason for litigation against GPs. Decision support is one possible intervention to help with this task, but existing systems lack evidence-based content, integration with the electronic health record (EHR), and have been designed with no regard for either the cognitive tasks of the GP or the human-computer interface needed to support them. Further, conducting large studies to develop diagnostic evidence is notoriously difficult and costly.