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. 2021 Feb 3;20:54. doi: 10.1186/s12939-020-01368-0

Fig. 1.

Fig. 1

Study population flowchart. From the original population consisting of data from respondents to 14 National Health Surveys (2004–2016, 2018), we excluded those with missing data on income or self-rated health (SRH), obtaining a final sample of 133,244 people