Review article: A primer for clinical researchers in the emergency department: Part XI. Inertia before investigation: Pre-test probability in emergency medicine.

In this series, we address research topics in emergency medicine. Rational clinical decision making is based on knowledge of the disease prevalence, clinical assessment features and test characteristics such as sensitivity and specificity. The concept of pre-test probability is important as it will allow the clinician and patient decide together if a 'test threshold' or 'treatment threshold' has been reached, or if further investigations are required to make such a decision. This research primer uses three case scenarios to explore these concepts.