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Control variables for back pain: age and sex (wave 2)
| Variable | Absolute frequency (%) |
|---|---|
| Age (years) | |
| 10 | 302 (14.7) |
| 11 | 359 (17.6) |
| 12 | 336 (16.5) |
| 13 | 299 (14.7) |
| 14 | 265 (13) |
| 15 | 231 (11.3) |
| 16 | 198 (9.7) |
| 17 | 50 (2.5) |
| Sex | |
| Boysa | 1,098 (53.8) |
| Girls | 942 (46.2) |
Note:
Reference categories of items in regression analyses.
