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Joinpoint two-phase fitting for 45 Chinese cities, showing the transition point below a threshold of 30 cases. The abbreviations next to the city names represent the names of the corresponding Chinese provinces (AH: Anhui; BJ: Beijing; CQ: Chongqing; GD: Guangdong; HLJ: Heilongjiang; HN: Henan; HB: Hubei; HN: Hunan; JX: Jiangxi; SX: Shaanxi; SH: Shanghai; SC: Sichuan; TJ: Tianjin; ZJ: Zhejiang). Fittings for individual cities are shown in Figure S2.
