To the Editor: I am writing this letter for 2 purposes. First, I want to comment on 2 articles in the March 2004 issue of Physical Therapy —the Research Report by Dumas et al titled “ Recovery of Ambulation During Inpatient Rehabilitation: Physical Therapist Prognosis for Children and Adolescents With Traumatic Brain Injury ”1 and the Update by Aldrich and Hunt titled “ When Can the Patient With Deep Venous Thrombosis Begin to Ambulate ?”2 Second, in the context of those articles, I want to briefly address the issue of evidence-based practice. Each article addressed important clinically relevant issues. Specifically, Dumas et al addressed ambulation prognosis after traumatic brain injury in children, and Aldrich and Hunt addressed the decision to ambulate after deep venous thrombosis (DVT). Each article also referred to the presence or absence of relevant evidence in literature. In the systematic retrospective study of ambulation prognosis, the authors concluded that lower-extremity (LE) hypertonicity, brain injury, and LE injury were the best predictors of ambulation ability. Is this conclusion anything other than confirmation of an obvious common-sense appraisal of gait potential? That is, the more severe the injury and the LE dysfunction, the worse the prognosis for ambulation. Could it be otherwise? I commend the authors for noting and defining the concepts of sensitivity and specificity, as well as acknowledging the high number of false positives and false negatives. I would like to translate the sterile notion of false positives and false negatives into clinical terms. A false positive would mean telling a child's family that their injured child is not expected to walk, but then the child does; a false negative would mean telling them that their injured child is expected to walk, but then the child does …