Table 1 Demographic characteristics of the study subjects

No. of subjects, n

10,127

2,327

7,800

Mean age ± SD, years

56.5 ± 9.4

58.0 ± 9.8

56.1 ± 9.2

Sleep duration ± SD, hours per day

6.6 ± 1.1

6.7 ± 1.1

6.4 ± 1.2

Sleep quality, n (%)

 “1” for very poor

1: 271 (2.7)

1: 37 (1.6)

1: 234 (3.0)

 “2” for poor

2: 1,927 (19.0)

2: 355 (15.3)

2: 1,572 (20.2)

 “3” for fair

3: 4,374 (43.2)

3: 950 (40.8)

3: 3,424 (43.9)

 “4” for good

4: 2,140 (21.1)

4: 571 (24.5)

4: 1,569 (20.1)

 “5” for very good

5: 1,412 (13.8)

5: 414 (17.8)

5: 998 (12.8)

Sleep timing, n (%)

 (1) 0–4 AM

(1): 2,071 (20.5)

(1): 440 (18.9)

(1): 1,631 (20.9)

 (2) 4–8 AM

(2): 23 (0.2)

(2): 11 (0.5)

(2): 12 (0.2)

 (3) 8–12 AM

(3): 20 (0.2)

(3): 11 (0.5)

(3): 9 (0.1)

 (4) 12–16 PM

(4): 7 (0.1)

(4): 0 (0.0)

(4): 7 (0.1)

 (5) 16–20 PM

(5): 27 (0.3)

(5): 9 (0.4)

(5): 18 (0.2)

 (6) 20–24 PM

(6): 7,941 (78.4)

(6): 1,830 (78.6)

(6): 6,111 (78.3)