Table 5. Risk-adjusted in-hospital mortality rates and the differences according to the COVID-19 outbreak and the county income tax per capita.

In-hospital mortality rate		Before-COVID	After-COVID	Difference	Difference-in-Difference
		Adjusted rate (95% CI)	Adjusted rate (95% CI)	Adjusted rate (95% CI)	Adjusted rate (95% CI)
Total		1.50% (1.49 to 1.52)	1.82% (1.80 to 1.83)	0.31% (0.30 to 0.33)
Income tax per capita
	Q1 (Highest)	1.53% (1.50 to 1.55)	1.81% (1.78 to 1.83)	0.28% (0.25 to 0.31)	Reference
	Q2	1.46% (1.43 to 1.48)	1.68% (1.66 to 1.71)	0.23% (0.20 to 0.25)	−0.06% (−0.10 to −0.02)
	Q3	1.53% (1.51 to 1.55)	1.82% (1.80 to 1.84)	0.29% (0.26 to 0.32)	0.00% (−0.04 to 0.05)
	Q4	1.49% (1.47 to 1.51)	1.96% (1.93 to 1.98)	0.47% (0.44 to 0.49)	0.18% (0.14 to 0.23)

Adjusted for year of visit, age, sex, insurance, community factors (per capita income tax, employment rate, and proportion of service/sales workers), and interaction term (year of visit × quartile of county income tax).

COVID-19 = coronavirus disease 2019, CI = confidence interval.