Seasonal trends in the mean and variance of ED visits. Mean number of ED visits (left axis, solid blue line) and mean variance in ED visits (right axis, dashed green line) as a function of the day of year. Data were smoothed using 5-day and 11-day moving averages, respectively. The ED utilization mean and variance are highest in the winter and lowest during the summer.
Wieland et al. BMC Medical Informatics and Decision Making 2007 7:15 doi:10.1186/1472-6947-7-15