Demographic characteristics of the 1,783 blood donors.

†To ensure good representativeness for each region (see Figure 1), sample size estimation for each center was based on the proportion of each center’s blood donation from 2008 to 2009, as listed below:Taipei (northern Taiwan, regional population: 6,963,205) had 518,696 blood donations in 2008 and 533,399 blood donations in 2009.Hsinchu (northwestern Taiwan, regional population: 3,462,995) had 253,678 blood donations in 2008 and 243,416 blood donations in 2009.Taichung (central Taiwan, regional population: 4,479,052) had 366,167 blood donations in 2008 and 365,843 blood donations in 2009.Tainan (southwestern Taiwan, regional population: 3,429,697) had 276,218 blood donations in 2008 and 290,406 blood donations in 2009.Kaohsiung (southern Taiwan regional population: 3,749,737) had 311,525 blood donations in 2008 and 313,686 blood donations in 2009.Hualien (eastern Taiwan, regional population: 1,035,086) had 81,473 blood donations in 2008 and 82,434 blood donations in 2009.