Exploring Delayed Pediatric Diagnoses in Emergency Department—Reply

In Reply We appreciate the criticisms raised by Tsai and Ma. We believe their concerns do not substantively impact our findings. Higher volume is clearly associated with improved patient outcomes, but prior to our study, that association had not clearly been extended to diagnostic quality. Emergency department (ED) volume is a marker of clinical experience, which itself is related to expertise. Experience and expertise matter in diagnostic quality. Experience and expertise are difficult to measure directly, but both attributes are associated with patient volume; clinician background; patient population; setting; hospital resources; such as the presence of inpatient beds that support pediatric care; and more. That is, those nonvolume factors mediate, not confound (as proposed by Tsai and Ma), the volume-delayed diagnosis association we observed across nearly 59 000 ED encounters. By definition, mediators should not be adjusted because they are the reason an association exists. For example, it would stand to reason that the staffing of pediatric specialists or the availability of 24-hour imaging would only exist in hospitals with higher pediatric volume and would tend to reduce the likelihood of delayed diagnosis. In that case, such resources would provide a reason for a volume-delay association, rather than causing such an association to be incorrect.