In Reply: We agree with Dr Lauderdale's observation that the availability of radiologists to read emergency department CT or MRI scans may confound the association between calendar year and the prevalence of CT or MRI scan use. However, we disagree with his suggestion that this may be addressed by comparing subgroup analyses for daytime shifts with those at night or on weekends. Doing so would assume that the only explanation for a differential increase in the prevalence of CT or MRI scan use based on day and time of emergency department presentation would be the availability of radiologists. However, there are other potential explanations, such as the effect of emergency department overcrowding during certain hours of the day, the availability of CT or MRI scan technicians, and potential differences in physician staffing patterns. Unfortunately, there is no covariate in the National Hospital Ambulatory Medical Care Survey database that can be used as an appropriate surrogate measure of the availability of radiologists.
Korley FK, Pham JC, Kirsch TD. Advanced Radiology in US Emergency Departments—Reply. JAMA. 2011;305(2):148-149. doi:10.1001/jama.2010.1955