Crude incidence rate ratio (IRR) of malignant cutaneous melanomas in pterygium and control cohorts
| Pterygium | Controls | ||||||
| Number | PY | Rate* | Number | PY | Rate* | IRR (95% CI) | |
| All | 646 | 346 371 | 186.5 | 530 | 333 847 | 158.8 | 1.2 (1.0 to 1.4) |
| Sex | |||||||
| Male | 466 | 220 395 | 211.4 | 388 | 212 653 | 182.5 | 1.2 (1.0 to 1.4) |
| Female | 180 | 125 976 | 142.9 | 142 | 121 194 | 117.2 | 1.2 (1.0 to 1.5) |
| Age group | |||||||
| <50 years | 228 | 209 021 | 109.1 | 184 | 205 320 | 89.6 | 1.2 (0.9 to 1.5) |
| >49 years | 418 | 137 350 | 304.3 | 346 | 128 527 | 269.2 | 1.1 (1.0 to 1.3) |
| Residential postcode | |||||||
| Metropolitan | 437 | 237 943 | 183.7 | 351 | 225 103 | 155.9 | 1.2 (1.0 to 1.4) |
| Regional | 192 | 95 240 | 201.6 | 173 | 95 316 | 181.5 | 1.1 (0.9 to 1.3) |
| Tropical | 17 | 13 188 | 128.9 | 6 | 13 428 | 44.7 | 2.9 (2.5 to 3.2) |
*Per 100 000 PY.
PY, total person-years in the study.