Figure 3.

Change in the 95% confidence interval (dashed lines) for the mean estimated H1N1 influenza infection rate (solid line) with different sample sizes using 4 different estimation methods, Singapore, 2009. A) Method 1; B) method 2; C) method 3; D) method 4; E) method 4 (see Table 2). Sample sizes which resulted in a 5- and 10-percentage-point spreads in the confidence interval for the mean estimates are shown with dotted vertical lines; the actual sample size used in the Singapore studies is shown with a circle on the x-axis. The total number of general practitioners (GPs) in Singapore in 2009 was approximately 2,138.