Table 3 Frequency and age of onset by NSSI type in overall study sample and across genders
|  | Overall (N = 2600) | Females (N = 1219) | Males (N = 1381) |  | Age of onset | |||
|---|---|---|---|---|---|---|---|---|
N | Wt % | N | Wt % | N | Wt % | χ2 p-value | Mean (SD) | |
Cutting | 364 | 13.4 | 257 | 19.0 | 107 | 7.7 | < 0.001 | 15.1 (3.6) |
Burning with cigarette | 42 | 1.3 | 14 | 0.9 | 28 | 1.7 | 0.245 | 16.7 (2.3) |
Burning with lighter or match | 50 | 1.6 | 23 | 1.5 | 27 | 1.7 | 0.671 | 15.8 (2.4) |
Carving words into skin | 77 | 2.6 | 53 | 3.5 | 24 | 1.7 | 0.010 | 15.1 (3.5) |
Carving pictures or marks into skin | 60 | 2.3 | 33 | 2.8 | 27 | 1.9 | 0.316 | 16.5 (5.5) |
Severe scratching | 215 | 7.9 | 152 | 11.4 | 63 | 4.3 | < 0.001 | 15.3 (4.6) |
Biting | 64 | 2.3 | 35 | 2.7 | 29 | 1.9 | 0.404 | 14.5 (4.6) |
Rubbing sandpaper | 13 | 0.5 | 4 | 0.4 | 9 | 0.6 | 0.573 | 14.0 (3.0) |
Dripping acid | 4 | 0.1 | 2 | 0.2 | 2 | 0.1 | 0.747 | 18.0 (5.3) |
Using bleach to scrub the skin | 3 | 0.1 | – | – | 3 | 0.2 | – | – |
Sticking sharp object into the skin | 75 | 2.7 | 45 | 3.4 | 30 | 1.9 | 0.047 | 14.4 (4.5) |
Rubbing glass | 11 | 0.4 | 8 | 0.5 | 3 | 0.2 | 0.405 | 15.7 (2.9) |
Breaking bones | 11 | 0.4 | 5 | 0.4 | 6 | 0.4 | 0.502 | 16.8 (3.5) |
Banging head | 130 | 4.9 | 53 | 4.5 | 77 | 5.3 | 0.285 | 16.2 (5.7) |
Punching oneself | 136 | 4.9 | 61 | 4.6 | 75 | 5.2 | 0.802 | 16.7 (4.9) |
Preventing wounds from healing | 58 | 2.3 | 41 | 3.4 | 17 | 1.1 | < 0.001 | 13.0 (5.4) |
Other forms | 63 | 2.6 | 37 | 3.3 | 26 | 1.9 | 0.016 | 16.3 (4.5) |