Table 1. Prevalence of chronic obstructive pulmonary disease in 2015, stratified by age and income.

	Total (%)	Male (%)	Female (%)
Age, yr
≥40	13.4	21.6	5.8
≥65	28.1	45.5	13.7
Age group, yr
40–49	4.1	7.3	0.8
50–59	9.7	16.8	2.4
60–69	21.2	34.1	11.4
≥70	30.6	51.7	13.6
Income*
Low	14.6	23.2	5.9
Low–middle	15.0	24.5	6.8
Middle–high	11.8	19.6	4.4
High	12.2	19.2	6.0

^*Income was categorized by ranking according to gender and age group at 5-year intervals. Each subject's income was calculated by dividing the total household income by the square root of the number of members in the household.