In reply:

We appreciate the letter by Tran et al1 and essentially agree with their comments. Their first concern is the use of a decision rule validated in one population of subjects but applied to a population with potentially different characteristics. Although a derivation-validation study conducted with a population with minimal head injury would have been ideal, we neither had the resources to perform such a study nor believed such an effort was necessary. Risk factors for consequential head injury have been explored in many patient populations and clinical settings already2-4 and finding additional factors seemed unlikely.

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