Frequencies and descriptive characteristics of NSSI
Of the 55% (n=349) of the overall sample who endorsed engaging in one or more of the 12 NSSI behaviors in the past year, 44% (n=279) endorsed the item ‘picked at a wound’, suggesting that this may be a clinically insignificant behavior among adolescent participants. We conservatively chose to eliminate from further analyses those who endorsed only the item ‘picked at a wound’. Furthermore, 7% (n=27) of adolescents indicated that one or more of their self-reported NSSI behaviors was a suicide attempt. One of these reported a single episode of self-injury, describing it as ‘other’ (the only participant endorsing ‘other’ NSSI). Given our operational definition of NSSI (deliberate, direct destruction or alteration of body tissue without conscious suicidal intent), we chose to exclude this individual from further analyses but opted to include these remaining 26 participants, given their frequent NSSI (mean=90·5, s.d.=147·3).
Thus, 46·5% (n=293) of our sample endorsed engaging in NSSI in the past year. Those engaging in NSSI reported an average of 12·87 incidents (s.d.=29·4, median=4·0, mode=2·0, range=1–205). Frequencies of behaviors are presented in .
Descriptive characteristics of non-suicidal self-injury (NSSI) within the past year in a community sample of adolescents (n=293)a
The mean number of types of NSSI performed was 2·35 (s.d.=1·67, median=2·0, mode=1, range=1–10). Forty-two per cent of self-injurers (n=110) reported engaging in only one type of NSSI in the past year, while 52% (n=136) of self-injurers endorsed engaging in two to five different types of NSSI, and 6% (n=15) endorsed six or more different types of NSSI. Few self-mutilators endorsed receiving medical treatment for any of their injuries (3%).
Differences between minor and moderate/severe NSSI characteristics
We found that 18·8% (n=119) of the overall sample engaged in minor NSSI only and 27·7% (n=175) engaged in at least one act of moderate/severe NSSI. While the two factors are strongly correlated (r=0·458, p<0·01), there appear to be important distinctions between the two. Those individuals endorsing moderate/severe NSSI (n=175) were likely to engage in more types of NSSI [3·23 (s.d.=2·02) v. 1·45 (s.d.=0·71); t=−9·25, df=292, p<0·001] and more incidents of NSSI [63·89 (s.d.=131·50) v. 28·06 (s.d.=46·75); t=−2·83, df=268, p<0·01] over the previous year than those endorsing only minor NSSI. While the majority of self-injurers reported little forethought about their acts, moderate/severe injurers were more likely to contemplate NSSI before engaging in the behavior [31·1% v. 11·7%; χ2 (7, n=244)=19·23, p<0·01]. They were also more likely than minor injurers to report experiencing pain during NSSI [73·5% v. 55·3%; χ2 (5, n=282)=14·84, p<0·01], to have received medical treatment for their injuries [χ2 (1, n=197)=5·64, p<0·05], and to have used alcohol or drugs during NSSI [26·5% v. 3·4%; χ2 (2, n=289)=27·0, p<0·001].
Differences between minor NSSI, moderate/severe NSSI and non-injurers on demographic and clinical variables
There were no significant differences between groups by age, sex, socio-economic status (SES), living situation, or region of the country (see ). Evaluation of our two largest racial groups found that Caucasians were significantly more likely to engage in NSSI than African-Americans [χ2 (2, n=600)=12·16, p<0·01], with Caucasians more likely to engage in moderate/severe NSSI but African-Americans more likely to engage in minor NSSI.
Demographic and psychosocial characteristics of adolescent self-injurers compared to non-injurers
Evaluation of clinical variables revealed significant group differences in history of out-patient psychiatric treatment [χ2 (2, n=631)=42·04, p<0·001], psychiatric hospitalization [χ2 (2, n=629)=26·72, p<0·001], history of suicide attempt [χ2 (2, n=629)=75·61, p<0·001], and also level of current suicide ideation [F(2, 617)=82·25, p<0·001]. Considering only those findings associated with a p<0·01, Tukey post-hoc contrasts showed significant differences between non-NSSI and both the minor NSSI and moderate/severe NSSI groups, with moderate/severe self-injurers generally demonstrating the highest occurrence rates, the non-NSSI group the lowest, and the minor self-injurer group in between (see ).
Functions of NSSI
A CFA was conducted evaluating four models differing in the number of latent factors (1, 2, 3 and 4) suggested to represent underlying motivations for NSSI among adolescents. The four-factor model provided the best fit to data from this sample [χ2 (70, n=261)=103·64, p<0·05] and was consistent with other fit indices (data available upon request).
Overall, self-injurers endorsed an average of 4·76 (s.d.=5·56) individual motives for NSSI. Items on the intra-personal, automatic-reinforcement scales were endorsed by 22–28% of all self-injurers, while items on the social-reinforcement scales were endorsed by 19–31% of injurers. Thus, community adolescents reported engaging in NSSI to influence the behaviors of others, as well as to regulate their emotional states. No significant gender differences emerged when comparing the four motivational factors, although males were more likely than females to endorse the item ‘to make others angry’ [χ2 (1, n=259)=8·7, p<0·01] and females were more likely than males to endorse the item ‘to punish yourself’ [χ2 (1, n=258)=4·05, p<0·05].
presents items contained within the four-factor model of NSSI, as well as the percentage of those engaging in minor NSSI and moderate/severe NSSI who endorsed each of these items. Moderate/severe injurers endorsed more motivations for NSSI than minor injurers [6·7 (s.d.=6·0) v. 4·0 (s.d.=5·0), t=4·03, df=288, p<0·001). Indeed, minor injurers were more likely to deny engaging in NSSI for any of the reasons listed, as compared to moderate/severe injurers (21·2% v. 14·5%, t=4·17, df=288, p<0·001). Inter-correlational analyses noted that, while moderate/severe NSSI was highly correlated with all four latent factors (all p's<0·01), minor NSSI was correlated only with automatic-negative reinforcement (r=0·128, p<0·05) and automatic-positive reinforcement (r=0·212, p<0·01). All four functions were significantly related to clinical variables of history of psychiatric treatment, in-patient treatment, suicide attempt, and current suicide ideation (all p's<0·01).
Rate of reported reasons for engaging in minor and moderate/severe non-suicidal self-injury (NSSI)
Differences between NSSI suicide and non-suicide attempters
Given a lack of clear understanding in the literature on the relationship between NSSI and suicide attempt, we chose to investigate further the differences between those endorsing past year NSSI and a suicide attempt(s) (NSSI suicide; n=26) versus those endorsing past year NSSI without suicide attempt(s) (NSSI non-suicide; n=267). These two groups did not differ on demographic characteristics. Evaluation of clinical variables found that the NSSI suicide group was more likely than the NSSI non-suicide group to have a history of out-patient psychiatric treatment [χ2 (2, n = 293)=12·07, p<0·01], psychiatric hospitalization [χ2 (2, n=292)=14·27, p<0·001], and greater current suicide ideation [F(2, 283)=47·87, p<0·001]. The NSSI suicide group endorsed greater frequency of moderate/severe NSSI [65·88 (s.d.=115·23) v. 10·57 (s.d.=42·54), t=5·04, df=290, p<0·001] and used more types of NSSI [4·50 (s.d.=2·39) v. 2·32 (s.d.=1·66), t=6·11, df=290, p<0·001]. They also reported a greater number of reasons for NSSI than the NSSI non-suicide group [10·76 (s.d.=5·41) v. 5·09 (s.d.=5·52), t=4·91, df=287, p<0·001] and were more likely to endorse items from all four functions of NSSI (all p's<0·001).