We exploit an exogenous process change at two emergency departments (EDs) within a health system to test the theory that increasing capacity in a discretionary work setting increases wait times due to additional services being provided to customers as a consequence of reduced marginal costs for a task. We find that an increase in physician’s capacity for ordering ultrasounds (U/S) resulted in an 11.5 percentage point increase in the probability of an U/S being ordered, confirming that resource availability induces demand. Furthermore, we find that the additional U/S demand increased the time to return other radiological tests due to the higher demand placed on radiologists from the additional U/S. Consequently, the average length of stay (LOS) for patients with an abdominal complaint increased by nearly 30 minutes, and the waiting time to enter the ED increased by 26 minutes. We do not find any indications of improved performance on clinical metrics, with no statistical change in the number of admissions to the hospital or readmissions to the ED within 72 hours. Our study highlights an important lesson for process improvement in interdependent service settings: increasing process capacity at one step in the process can increase demand at that step, as well as for a subsequent shared service, and both can result in an overall negative impact on performance
