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. 2018 Sep 25;4(3):e65. doi: 10.2196/publichealth.8627

Figure 1.

Figure 1

Population bias in Twitter-based influenza surveillance. According to the geographic distribution in Japan of 7,666,201 influenza-related tweets for the period from 2012 to 2015, most Twitter users are in urban cities (such as Tokyo and Osaka). Other cities are adversely affected by a shortage of data that biases influenza detection there.