From April 1, 2004 to March 31, 2005 , data transmitted from the 189 hospitals on 2,692,325 ED visits were collected and stored in the Taiwan-CDC database. Initially, we appointed two computer engineers to cleanse the data by checking the log files and inform the hospitals by telephone on weekdays to correct errors or provide missing data. Then, these cleaned data on daily counts of ED visits collected from ED-SSS were analyzed. The time series plot of rough data on daily numbers of ED visits in our nationwide ED-SSS during the study period is shown in Figure 3 .