Table 2. Characteristics of the study population among tertiles of nonmethane hydrocarbons (NMHC) exposure.
| Characteristics | Tertiles of average daily NMHCa, n (%) | P valueb | Total (n = 837,917) |
||
|---|---|---|---|---|---|
| T1 (lowest) (n = 251,321) |
T2 (n = 294,887) |
T3 (highest) (n = 291,709) |
|||
| Retinal vein occlusion | 383 (0.2) | 351 (0.1) | 773 (0.3) | <0.001 | 1,507 (0.2) |
| Age, years | <0.001 | ||||
| Mean ± SD | 38.3 ± 18.5 | 27.4 ± 21.9 | 34.7 ± 18.9 | 33.2 ± 20.4 | |
| Gender | <0.001 | ||||
| Male | 130,689 (52.0) | 147,136 (49.9) | 153,704 (52.7) | 431,529 (51.6) | |
| Coronary artery disease | 34,868 (13.9) | 26,674 (9.0) | 28,385 (9.7) | <0.001 | 89,927 (10.9) |
| Chronic kidney disease | 17,570 (7.0) | 14,667 (5.0) | 16,385 (5.6) | <0.001 | 48,622 (5.9) |
| Chronic obstructive pulmonary disease | 26,852 (10.7) | 21,555 (7.3) | 21,093 (7.2) | <0.001 | 69,500 (8.4) |
| Asthma | 21,274 (8.5) | 31,047 (10.5) | 20,635 (7.1) | <0.001 | 72,956 (8.8) |
| Arrhythmia | 36,512 (14.5) | 27,802 (9.4) | 25,672 (8.8) | <0.001 | 89,986 (10.8) |
| Cerebrovascular diseases | 26,274 (10.5) | 19,592 (6.6) | 21,817 (7.5) | <0.001 | 67,683 (8.2) |
| Hypertension | 53,729 (21.4) | 41,463 (14.1) | 44,231 (15.2) | <0.001 | 139,423 (16.7) |
| Diabetes mellitus | 39,624 (15.8) | 30,669 (10.4) | 34,065 (11.7) | <0.001 | 104,358 (12.6) |
| Hyperlipidemia | 53,559 (21.3) | 43,259 (14.7) | 46,288 (15.9) | <0.001 | 143,106 (17.0) |
| Smoking-related diagnosis | 16,145 (6.4) | 12,068 (4.1) | 13,374 (4.6) | <0.001 | 41,587 (5.0) |
| Morbid obesity | 2,147 (0.9) | 2,102 (0.7) | 2,482 (0.9) | <0.001 | 6,731 (0.8) |
| Glaucoma | 7,127 (2.8) | 7,438 (2.5) | 7,294 (2.5) | <0.001 | 21,859 (2.6) |
| Hypercoagulable state | 1,921 (0.8) | 1,533 (0.5) | 1,975 (0.7) | <0.001 | 5,429 (0.7) |
| Retinal arteriolar disorder | 107 (0.04) | 88 (0.03) | 107 (0.04) | 0.046 | 302 (0.04) |
Note: SD, standard deviation.
aTertile values in ppm were as follows: T1 level: < 0.29, T2 level: ≥ 0.29 and < 0.36, T3 level: ≥ 0.36.
bThe chi-squared test or one-way analysis of variance among tertiles of non-methane hydrocarbons.