Table 1.

Name, source, and description of each explanatory variable considered

Data	Source	Description	Included in best model
Common cold	SIRS transmission model	4-d Aggregated common cold prevalence	*
Influenza prevalence	Hospitalization records	Daily state-level hospitalizations per million caused by influenza in adults and children (spline-smoothed)	*
Day of the week	Calendar		*
Time trend	Daily index value		*
Local intercept	Metropolitan boundary	Geographic variation in baseline hospitalization rate	*
Low temperature	CDC Wonder	Daily minimum temperature in counties in the metropolitan area (Celsius)	*
Ozone	AQS	Daily ozone (air quality index value)
PM 2.5	CDC Wonder	Maximum daily PM 2.5 for counties in the metropolitan area (micrograms per meter3)

A complete description of each model and estimated coefficients of each variable is in SI Appendix. AQS, air quality system; CDC, Centers for Disease Control and Prevention; PM, particulate matter.

^*The variable was included in the best fitting model.