Baseline characteristics of the 514 patients with primary spontaneous pneumothorax
| Variable | Overall | Female | Male |
| Patients | 514 | 75 (15%) | 439 (85%) |
| Age on first admission years | |||
| Median (range) | 25 (12–40) | 29 (15–40) | 24 (12–40) |
| Mean±sd | 25.7±7.1 | 29.2±7.2 | 25.1±6.9¶ |
| Lung affected initially | |||
| Right lung | 256 (53%) | 36 (48%) | 220 (50%) |
| Left lung | 254 (46%) | 37 (49%) | 217 (49%) |
| Bilateral | 4 (1%) | 2 (3%) | 2 (1%) |
| Body mass index kg·m−2 | |||
| Median (range) | 20.4 (12.7–33.2) | 20.4 (12.7–33.2) | 20.4 (13.9–29.2) |
| Mean±sd# | 20.7±3.1 | 20.9±4.5 | 20.7±2.7 |
| Smoking habits | |||
| Never-smokers | 136 (27%) | 22 (29%) | 114 (26%) |
| Daily smokers | 299 (58%) | 36 (48%) | 263 (60%) |
| Weekly smokers | 12 (2%) | 2 (3%) | 10 (2%) |
| Less than weekly | 8 (1.5%) | 3 (4%) | 5 (1%) |
| Ex-smokers | 21 (4%) | 8 (10%) | 13 (3%) |
| Unknown | 36 (7%) | 4 (5%) | 32 (7%) |
#: n=225. ¶: p<0.0001.