Before collecting study data, a decision was made to develop a URI symptom score measure that had "sensibility." This term is used to describe a decision rule that has face validity to clinicians caring for children (19, 20) . For example, if a symptom measure on days 2 and 4 of illness was associated with the outcome of a viral URI in the regression model, it would be sensible to also include scores for that symptom on days 1 and 3. Thus, additional models for the URI symptom score were developed by including symptom measures that we judged to increase the sensibility of the prediction rule. Alternative models of the score were developed in which one or more symptom measures were removed until the final model for the URI symptom score with the highest accuracy in differentiating children with and without a viral URI was derived. A final model, using the Jackson score, (8) was also constructed. For the Jackson score, the sum of the severity of eight symptom measures for 6 d is calculated; a score Ն14 is considered as indicative of a viral URI.