Table 2.
Baseline characteristics among subjects with different frequencies of self-reported depressive symptoms.
| Variable | Total | Self-reported depressive symptoms |
P-value for difference between groups | ||
|---|---|---|---|---|---|
| Often or always | Sometimes | Never or seldom | |||
| N | 40,902 | 2565 | 20,792 | 17,545 | |
| Mean age (SD) | 51.2 (16.0) | 52.6 (15.6) | 50.6 (16.1) | 46.1 (16.0) | <0.001 |
| Women, n (%) | 26,301 (64) | 1988 (78) | 14,573 (70) | 9740 (56) | <0.001 |
| University degree, n (%) | 11,534 (28) | 755 (29) | 5765 (28) | 5014 (29) | 0.065 |
| Working, n (%) | 20,274 (50) | 1220 (48) | 10,073 (48) | 8981 (51) | <0.001 |
| Retired, n (%) | 10,603 (26) | 395 (15) | 5179 (25) | 5029 (29) | <0.001 |
| Student, n (%) | 1604 (3.9) | 191 (7.5) | 943 (4.5) | 470 (2.7) | <0.001 |
| Unemployed, n (%) | 821 (2.0) | 87 (3.4) | 464 (2.2) | 270 (1.5) | <0.001 |
| Long-term sick-leave, n (%) | 670 (1.6) | 104 (4.1) | 382 (1.8) | 184 (1.1) | <0.001 |
| Other, n (%) | 1850 (4.5) | 113 (4.4) | 726 (3.5) | 597 (3.4) | 0.035 |
| Difficulty falling asleep, n (%) | 2243 (5.5) | 511 (20) | 1295 (6.2) | 437 (2.5) | <0.001 |
| Difficulty maintaining sleep, n (%) | 2922 (7.1) | 533 (21) | 1759 (8.5) | 630 (3.6) | <0.001 |
| Early morning awakening, n (%) | 3550 (8.7) | 542 (21) | 2039 (10) | 969 (5.5) | <0.001 |
| Tired at awakening, n (%) | 5934 (15) | 985 (38) | 3365 (16) | 1584 (9.0) | <0.001 |
| Daytime sleepiness, n (%) | 2955 (7.2) | 719 (28) | 1685 (8.1) | 551 (3.1) | <0.001 |
| Insomnia, n (%) | 2350 (5.8) | 591 (23) | 1353 (6.5) | 406 (2.3) | <0.001 |
| Mean sleep duration, hours/night (SD) | 6.8 (1.0) | 6.9 (0.8) | 6.8 (1.0) | 6.6 (1.2) | <0.001 |
| Often/always nightmares, n (%) | 407 (1.0) | 142 (5.5) | 206 (1.0) | 59 (0.3) | <0.001 |
| Sometimes nightmares, n (%) | 7496 (18) | 942 (37) | 4784 (23) | 1770 (10) | <0.001 |
| Current smokers, n (%) | 2957 (7.2) | 317 (12) | 1594 (7.7) | 1046 (6.0) | <0.001 |
| Past smokers, n (%) | 10,506 (26) | 640 (25) | 5319 (26) | 4547 (26) | 0.514 |
| BMI, kg/m2 (SD) | 24.6 (3.5) | 24.6 (3.3) | 24.6 (3.6) | 24.7 (4.1) | 0.462 |
| Low physical activity, n (%) | 6492 (16) | 568 (22) | 3326 (16) | 2598 (15) | <0.001 |
| Coffee, no of cups/daily (SD) | 2.9 (1.8) | 2.9 (1.8) | 2.8 (1.8) | 2.8 (2.0) | <0.001 |
| Alcohol drinkers, n (%) | 36,011 (88) | 2254 (88) | 18,360 (88) | 15,397 (88) | 0.251 |
| Standard glasses of alcohol per week (SD) | 6.3 (4.3) | 6.5 (4.4) | 6.2 (4.2) | 5.9 (4.2) | <0.001 |
| Cancer, n (%) | 2558 (6.3) | 164 (6.4) | 1355 (6.5) | 1039 (5.9) | 0.054 |
| Cardiovascular disease, n (%) | 4458 (11) | 274 (11) | 2307 (11) | 1877 (11) | 0.432 |
Differences in baseline variables across categories of nightmare frequency were assessed using one-way analysis of variance (ANOVA) for continuous variables and the Kruskal–Wallis test for categorical variables.