Patient Resident Time (PRT): The amount of time a patient spends in the healthcare system, typically measured from the moment they enter the system, until the time of their medical discharge.
Artificial Variability: The direct result of the poor management of the processes used to provide care. This type of variability (dysfunctional management and policies) can be reduced through improved operational policies and system design.
Natural Variability: A source of great waste in the health care delivery system is excessive variability in the processes used to provide care. Natural variability is largely outside the control of a hospital, and it includes “clinical” variability (patients differ in the type and severity of their diseases, and patients with similar ailments respond differently to treatment), “patient demand” variability (patients arrive for treatment randomly over time), and “professional” variability (different surgeons treat similar patients in different ways), which has given rise to the development of approaches like practice guidelines and clinical pathways.