Table 1. Characteristics of the KBD cases and controls.
| Characteristics | Cases(n = 638) | Controls(n = 324) |
| Age, mean ± SD | 53.3±13.07 | 54.5±15.81 |
| Sex, male/female | 244/394 | 157/167 |
| Degree | ||
| I | 241 | – |
| II | 336 | – |
| III | 60 | – |
| IV | 1 | – |
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