All candidate variables were entered into stepwise forward logistic analysis; the following symptom measures were included in the final model: significant runny nose, day 1; significant cough, day 4; significant runny nose, day 4; and any fever, day 3. Based on these symptoms, three models for a URI symptom score were developed. For each model, a score was derived by assigning one point for the presence of each symptom included in the measure. ROC analysis was then used to determine the cut-off score that maximized the accuracy of the model. The properties of each model as a URI symptom score are summarized in Table 5 . Model 1 included only the symptom measures included in the final forward regression analysis. For model 2, in which the "sensibility" of the prediction rule was improved, symptom measures for significant cough on days 1-3, significant runny nose on days 2 and 3, and any fever on days 1-2 and day 4 were included. Using systematic removal of different measures, the inclusion * Number of children with data for the symptom measure and excluding those for whom no data were available for that day, those whose parents did not rate the severity of the symptom, or whose parents indicated "can't tell" for the severity of the symptom. * One point was given for the presence of each symptom measure present and points summed for each child. The cut-off value was the score that best differentiated children with and without a viral URI.