One limitation of this study is that the diagnostic utility of our URI symptom score may be different in another population of children (28) . It is also possible that the utility of the symptom score would be different at another time when the distribution of circulating respiratory viruses is different. Subsequent investigation is needed to validate the URI symptom score that we developed. However, we purposefully incorporated a number of features into the development of the score that were designed to maximize its generalizability. First, rather than including symptom measures based solely on a statistical analysis, we modified the URI symptom score to have clinical "sensibility." The precision of the URI symptom score could have been increased in this particular population by weighting some symptoms (29) . We chose the more conservative approach of giving equal weight to relevant symptoms to minimize the effects of statistical quirks of the data set. Finally, we only included symptom measures for which Ͼ90% of parents could adequately rate severity. Because measures included in the URI symptom score (significant runny nose and cough) are intuitively important, it is more likely that the score will perform similarly in other children than if a more complicated prediction rule had been developed.