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Sex differences in NSSI in a college population 1
Non-Suicidal Self-Injury in a College Population: General Trends and Sex Differences*
Janis Whitlock, MPH, PhD
1,2
, Jennifer Muehlenkamp, PhD
3
, Amanda Purington, MPS
1
, John
Eckenrode, PhD
1,2
, Paul Barreira, MD, MPA,
4
Gina B. Abrams, MPH, MSW
5
, Tim Marchell,
PhD
6
, Victoria Kress, PhD
7
, Kristine Girard MD
8
, Calvin Chin, PhD
9
, Kerry Knox, PhD
10
From the Family Life Center Center,
1
Department of Human Development
2
, University of
Wisconsin-Eau Claire, Eau Claire, WI
3
; Harvard University Health Services, Cambridge, MA
4
;
Princeton University, Princeton, New Jersey
5
; Gannett Health Services
Cornell University,
Ithaca, New York
6
; Youngstown State University, Youngstown, Ohio
7
; MIT Medical
Massachusetts Institute of Technology, Cambridge, Massachusetts
8
; Columbia University, New
York, New York
9
; University of Rochester, Rochester, New York
10
April 20, 2010
Accepted for publication September, 2010 in Journal of American College Health
For correspondence or reprints, please contact:
Janis Whitlock, MPH, PhD
Family Life Development Center
Cornell University
Ithaca, NY 14853
Telephone: (607) 254-2894; Facsimile: (607) 255-8562
E-Mail: jlw43@cornell.edu
Sex differences in NSSI in a college population 2
ABSTRACT
Objective: To describe basic non-suicidal self-injury (NSSI) characteristics and to explore sex
differences.
Method: A random sample from eight universities were invited to participate in a web-based
survey; 38.9% (n=14,372) participated. Analysis assessed sex differences in NSSI prevalence,
practices, severity, perceived dependency, and help-seeking; adjusted odds ratios for NSSI
characteristics were calculated by sex status.
Results: Lifetime NSSI prevalence rates averaged 15.3%. Females were more likely than males
to self-injure because they were upset (AOR 1.6, 95% CI 1.3-2.1) or in hopes that someone
would notice them (AOR 1.6, 95% CI 1.1 – 2.7). Males were 1.6 times (95% CI, 1.2 – 2.2) more
likely to report anger and 4.0 times (95% CI, 2.3 – 6.8) more likely to report intoxication as an
initiating factor. Sexual orientation predicted NSSI, particularly for women (Wald F=8.81,
p<.000). Only 8.9% of the NSSI sample reported disclosing NSSI to a mental health
professional.
Conclusions: NSSI is common in college populations but varies significantly by sex and sexual
orientation. NSSI disclosure is low among both sexes.
Key Words: self-injury; young adults; mental health
Sex differences in NSSI in a college population 3
INTRODUCTION
Non- suicidal self-injury (NSSI) is common among community populations of youth and
poses an overlooked public health challenge on college campuses. Defined as behaviors in
which an individual intentionally harms the body without overt suicidal intent and for reasons
that are not socially sanctioned., NSSI typically entails behaviors such as cutting, burning,
scratching, and self-battery.
1,2
Studies within adolescent samples show markedly high lifetime
NSSI prevalence rates of 12% to 47%,
2-10
while lifetime rates among college students have been
estimated at 17% to 38%.
11-15
Although the severity and lethality of NSSI varies by individual
and population, its link with suicide behavior, psychological distress, disordered eating, and
other forms of mental illness
7,16-18
is well documented and points to the need for increased
understanding of NSSI characteristics and intervention and prevention opportunities.
Although basic epidemiological and clinical characteristics of NSSI, such as lifetime
frequency, age of onset, affected body parts, and form (e.g., cutting, burning etc.) are well-
studied,
10,11,17,19
very large and notable gaps in knowledge remain. For example, little is known
about the external and internal contexts which contribute to the adoption of NSSI, specific
routines and habits, contexts within which individuals injure themselves more severely than
intended, perceived dependency, and trends in disclosure and help-seeking. Establishing
knowledge in these areas is critical in moving beyond clinical treatment and into early
intervention and prevention, since despite its prevalence, it is rare for NSSI to attract clinical
attention until it is quite advanced and difficult to treat.
The role of sex and sexual orientation in NSSI is similarly under-explored but of high
importance since both areas have been identified as highly salient in intervention and prevention
efforts.
11,20
Although many studies show NSSI to be more common in females
3,5,11,21,22
a number
Sex differences in NSSI in a college population 4
of studies show no difference in prevalence in males and females.
4,15,23-25
Moreover, only limited
research has examined sex differences in NSSI characteristics. The studies that do exist are often
limited by inclusion of suicide behavior as part of NSSI
3
and by the assessment of a restricted
range of NSSI behaviors.
26
Similarly, while the evidence supporting NSSI as an emotion-
regulating behavior is strong
3,19,27,28
there is little understanding of how the psychological
functions underlying NSSI vary by sex. Previous studies identify arms, hands, wrists, thighs, and
stomach as the primary sites for NSSI activity
11,26
but, as with function, there exists little
understanding of whether males and females are likely to present with differential wound
locations. Moreover, no findings related to sex have been reported on NSSI initial motivation,
routines and habits, unintended severity, perceived dependency, or disclosure and help-seeking.
Equally understudied are differences in NSSI prevalence by sexual orientation, despite multiple
indications that these differences may be marked and may interact with sex.
11,20
Given sex related differences in disorders related to NSSI, such as suicide behavior and
disordered eating,
29
it is likely that there are sex differences in NSSI behaviors with important
implications for its detection and treatment as well as for intervention and prevention. This study
analyzes data from the largest study conducted in a college population to describe basic NSSI
characteristics and to explore sex differences.
METHODS
Sample
A random sample of 36,900 students from eight colleges and universities in the Northeast
and Midwest was invited to participate in a web-based “Survey of Student Well Being” (SSWB)
in the fall of 2006 and early winter of 2007. Five of the eight schools were private, one was a
mix of public and private, and two were public. All but two are located in largely urban areas.
Sex differences in NSSI in a college population 5
School size and population varied considerably ranging from fewer than 2000 undergraduates to
over 11,000 undergraduates. The sample was randomly drawn by each University Registrar
using specialized software. The demographic profile of those invited matched the student
population of these universities. Invitees were sent an e-mail containing descriptive information
and a link to the survey.
Response rates from each university ranged from 20% - 48% with a total of 14,372
respondents (38.9%). This is consistent with response rates from studies with similar
populations.
26
Respondents were largely undergraduate students, but two schools included
graduate students as well. Cases in which NSSI status was not determinable due to missing data
(n=812, .05%) were excluded. To better reflect the extent of NSSI in the young adult population,
analyses were limited to young adult respondents (under age 25). A total of 11,529 respondents
were retained for analysis. The sample was representative of the overall student population
across all 8 universities in terms of ethnicity, age, and socioeconomic status although more
females than males participated (57.6% vs. 41.7%). Representativeness was established by
comparing study sample demographics (sex, race/ ethnicity, and SES) to the student population
universe from which the sample was drawn.
Study Design and Questionnaire
The survey was administered on a secure Internet server and required 15-30 minutes to
complete. The study was approved by all participating universities’ Committee for Human
Subjects. All participants provided on-line consent before taking the survey and were free to
discontinue at any time. Multiple response enhancement strategies (e.g., incentives, follow-up
reminders, personalized invitations) were employed. Links to local mental health resources were
provided throughout the survey.
Sex differences in NSSI in a college population 6
Assessment of NSSI and Correlates
NSSI was assessed using the Non-Suicidal Self-Injury Assessment Tool (NSSI-AT),
developed for a previous study.
11
An initial screening question for self-injurious behavior, “Have
you ever done any of the following with the purpose of intentionally hurting yourself?” is
followed by a list of 19 NSSI behaviors. Participants were then asked a series of closed ended
questions that assessed general NSSI characteristics: age of onset and cessation, lifetime
frequency, last time individual self-injured, psychological functions (e.g., stress relief;),
motivations for initiating NSSI (e.g., self anger), body areas affected (e.g., arms, legs), routines
and habits (e.g., self-injure in private setting only), perceived dependency (e.g., inability to
control urge to self-injure), unintended severity (e.g., self-injured more severely than expected),
and help-seeking and disclosure (e.g., saw a mental health professional). These questions were
created through a review of the literature, including existing scales, as well as in-depth
interviews conducted with individuals with a history of self-injury as well as mental health
providers with experience in this area. In order to better understand differences in NSSI function
category by sex, function items were grouped into six categories based on function similarity: a)
affect regulation, b) social response, c) sensation seeking, d) self-punishment, e) self-control, and
f) uncontrolled urge.
In order to better understand the relationship between NSSI and suicide, suicidal intent is
not screened out in the preliminary NSSI assessment stage; rather this is accomplished through
assessment of function. Included in the list of NSSI function were items which assessed suicidal
intent. Individuals who indicated that they use the behaviors assessed in the NSSI screening
question as a means of practicing or attempting suicide were removed from the NSSI sample
(n=28).
Sex differences in NSSI in a college population 7
Demographic characteristics assessed included: sex, age, sexual orientation, international
student status, race/ethnicity, and father’s education level (used as a proxy for SES). These items
are reported in more detail in a paper reporting results from another college study using the
SSWB.
11
The sexual orientation variable which was patterned after Kinsey’s conceptualization
of a continuum of attraction (e.g., “Are you sexually attracted to or aroused by: only males,
mostly males, more to males but significantly to females” etc.). Response categories were
collapsed to create a 5 category sexual orientation variable (e.g., heterosexual orientation, mostly
heterosexual orientation, bisexual, mostly gay/lesbian, gay/lesbian).
Statistical Analyses
All analyses were weighted to account for the greater number of female respondents
using the complex samples module of SPSS version 15 (SPSS Inc., Chicago, Ill.). Generalized
linear models were constructed to examine the relationship between NSSI and all correlates.
Logistic regressions were computed for dichotomous outcomes and negative binomial
regressions were computed for count outcomes. For all models, sexual orientation, ethnicity, and
international student status were included as covariates. Table 1 provides descriptive statistics for
the sample as a whole and by sex. The effect of sex in the multivariate models is reported either
as an odds ratio or as a factor change in the number of events (continuous variables), as
appropriate (exp(B)).
RESULTS
Overall NSSI Prevalence by Demographic Characteristics
The overall sample contained significantly more females than males and over half
(64.3%) were Caucasian (see Table 1). The majority (90.5%) were attending college as domestic
students, and most of the students reported that their fathers had a college education. Nearly
Sex differences in NSSI in a college population 8
three quarters (76.1%) of the sample reported being exclusively heterosexual while the
remainder reported greater variability in sexual attraction.
Of the 11,529 individuals included in these analyses, 1,776 (15.3%, 95% CI 14.6-16.1)
reported NSSI at some point in their lives. The prevalence rate for the previous 12 months was
6.8% (n=789). Adjusted odds ratios comparing demographic characteristics of those with and
without NSSI history are shown in Table 1. Females were 1.8 times (95% CI, 1.6-2.0) more
likely than males to report NSSI (18.9% vs. 10.9%) but were not significantly more likely to
report self-injury within the past 12 months. International students were slightly less likely to
report NSSI (AOR .7, 95%, CI .5-.9). The mean age of those reporting NSSI was 20.3 years
(SD= 1.8) and did not differ from the overall study sample (20.5; SD=1.9). Compared with their
Caucasian counterparts, Asian/Asian Americans were slightly less likely to report NSSI (AOR
.8, 95% CI, .7-.9).
------------------
Insert Table 1 about here
------------------
There were no other demographic differences in NSSI prevalence other than sexual
orientation. Individuals with sexual orientations other than exclusively heterosexual were at
significantly elevated risk for NSSI. Compared to heterosexuals, individuals characterized as
mostly heterosexual were 2.6 times (95% CI, 2.2-3.0) more likely to report NSSI. Comparable
statistics for individuals characterized as bisexual are as follows: 3.8 times (95% CI, 3.1-4.6), for
individuals characterized as mostly gay or lesbian: 2.3 times (95% CI, 1.6-3.5), and for
individuals characterized as gay or lesbian: 1.7 times (95% CI, 1.1-2.5). There was a significant
Sex differences in NSSI in a college population 9
interaction between sexual orientation and sex (Wald F=8.81, p<.000). Tests for simple effects
showed that the relationship between NSSI and sexual orientation was confined largely to
females. Other than the significant difference between heterosexual males and mostly
heterosexual males (AOR 2.1, 95%, CI 1.5-2.8), there were no statistically significant differences
in NSSI status among males by heterosexual status. Heterosexual females were 1.5 times (95%
CI, 1.3–1.8; 13.5% female vs. 9.7% male) more likely to report any NSSI than their male
counterparts; mostly heterosexual females 2.1 times (95% CI, 1.6-2.8; 29.5% vs. 19.5%),
bisexual females 6.2 times (95% CI, 3.7-10.4; 49.4% female vs. 13.7% male), mostly gay
females 5.5 times (95% CI, 2.2-13.6; 22.9% vs. 10.4%) and lesbians 2.4 times (95% CI, 1.1-5.5;
49.0% female vs. 13.1% male). There were no other demographic differences in NSSI
prevalence.
NSSI Characteristics in the NSSI Sample and by Sex
Table 2 shows lifetime frequency, dominant form, and number of forms used across the
NSSI sample and by sex. Demographic characteristics held constant in these analyses are those
which emerged from the first analysis as significant and include: sexual orientation and
race/ethnicity. Analyses for this section include only individuals with a history of any NSSI (the
“NSSI sample”). The average age of onset was 15.2 years with 22.7% indicating that they
initiated NSSI between the ages of 18-22; 7% (n=124) started at age 10 or younger; 7% (n=124)
started at age 10 or younger. Of the 19 NSSI behaviors presented, those endorsed by more than
10% of the NSSI sample are shown in Table 2. Most (n= 1,534; 86.4%) NSSI sample
respondents indicated having engaged in NSSI more than once and nearly half (n=760; 42.8%)
indicated having engaged in NSSI on 6 or more occasions. Over half (63.3%) of those with
repeat NSSI experience reported using more than one form of the behavior.
Sex differences in NSSI in a college population 10
------------------
Insert Table 2 about here
------------------
Adjusted odds ratios of NSSI frequency, form, and number of forms used comparing
males and females are also shown in Table 2. Females were significantly more likely than males
to report over 20 NSSI incidents (AOR 1.7, 95% CI 1.1-2.8), and to report scratching (AOR 2.5,
95% CI 1.9-3.2) and cutting (AOR 2.7, 95% CI 2.1-3.5). Males were 3.4 times (95% CI, 2.6-4.5)
more likely than females to say that they had punched an object with the intention of hurting
themselves.
Table 3 shows psychological NSSI function by category, initial reason for self-injuring (7
of 18 endorsed by >2% of the NSSI sample), primary body parts affected (8 of 17 endorsed by
>10% of the NSSI sample), routines and habits, perceived dependency, unintended severity, and
help-seeking patterns across the NSSI sample and by sex. Females were significantly more likely
than males to endorse using NSSI to regulate affect (AOR 1.6, 95% CI 1.2-2.2), as a form of
self-control (AOR 1.8, 95% CI 1.3-2.6), and because they experience an overwhelming urge
(AOR 1.4, 95% CI 1.1-2.0). Males were 1.4 times (95% CI, 1.1-1.9) more likely than women to
endorse functions related to stimulation (e.g., “to get a rush or surge of energy”).
------------------
Insert Table 3 about here
------------------
Females were significantly more likely to report damage to their arms (AOR 1.5, 95%
CI, 1.2 – 1.9), wrists (AOR 3.8, 95% CI, 2.8-5.1), thighs (AOR 2.1, 95% CI 1.5-2.9), and
calves/ankles (AOR 3.6, 95% CI 2.3 – 5.5). Males were 2.1 times (95% CI, 1.6-2.7) more likely
Sex differences in NSSI in a college population 11
than females to report damage to hands. Sex differences were also evident in initial motivation
for NSSI. Although females were more likely to report being upset (AOR 1.6, 95% CI 1.3-2.1)
or hoping someone would notice their self-injury (AOR 1.6, 95% CI 1.1 – 2.7), males were 1.6
times (95% CI, 1.2 – 2.2) more likely to report being angry at someone and 4.0 times (95% CI,
2.3 – 6.8) more likely to report being drunk or high the first time they self-injured.
Males and females also show significant differences in NSSI routines and habits. Females
were more likely to report injuring in private (AOR 2.5, 95% CI 1.9 – 3.2), going through phases
marked by high and low NSSI activity (AOR 2.1, 95% CI 1.5 – 3.1), and having friends who
self-injure (AOR 1.4, 95% CI, 1.1 – 2.1). Males were more likely to report sometimes injuring in
the presence of others (AOR 2.4, 95% CI, 1.5 – 3.6), letting others cause injuries (AOR 3.6, 95%
CI, 1.9 – 6.9), or injuring another person as part of a routine (AOR 4.4, 95% CI, 2.2 – 7.5).
Just under half (41.2%) of all NSSI sample respondents reported either one of the two
NSSI perceived dependency measures. Females were 1.9 times (95% CI, 1.3-2.7) more likely to
report difficulty controlling the urge to self-injure and 1.9 times (95% CI, 1.4-2.6) more likely to
believe that NSSI is a problem in their lives.
Just over 1 in 5 of the NSSI sample (21.1%) indicated that they had injured themselves
more severely than expected. Of these (n=351), 20.2% indicated that they were under the
influence of drugs and alcohol when this occurred, with males significantly more likely (AOR
1.9, 95% CI 1.1-3.1) to report this condition. Of those who reported injuring themselves more
severely than expected, over one-third (39.6%) felt they should have sought medical care but did
not (7.8% of the NSSI sample). Five percent of the NSSI sample reported seeking medical
treatment for injuries; this did not vary by sex.
Sex differences in NSSI in a college population 12
With regard to disclosure and help-seeking, 22.6% of the NSSI sample reported that no
one knew about their NSSI; no significant difference was found by sex. Over half (52.3%) had
been to therapy for any reason, with females 2.0 times (95% CI, 1.6-2.6) more likely than males
to do so. Only 8.9% of the NSSI sample reported disclosing NSSI behavior to a mental health
professional; this did not significantly vary by sex.
DISCUSSION
Findings from the current study support the contention that NSSI is a widespread
behavior in adolescent and young adult populations,
10,11,17,21
as suggested by the lifetime
prevalence rate of 15.3% and previous year rate of 6.8% in this sample. These rates are
comparable to other studies
3,5,11,15,21,24,30
and suggest that NSSI exists at epidemic proportions in
community populations of youth. Although often written off as an immature and attention
seeking behavior, the presence of NSSI in college populations (22.7%) and the relationship
between NSSI and suicide
4,23,29
suggest that NSSI may serve as a harbinger of more lethal
behaviors for the current generation of youth and may thus serve as an important indicator for
early intervention.
Adding to the set of studies which document a difference in NSSI by sex, females in this
study were nearly twice as likely to report NSSI than males (18.9 % versus 10.9%),
3,11,31,32
and to
report more lifetime incidents of NSSI. Males were, however, equally likely as females to report
self-injury in the past year, a finding consistent with studies reporting no difference in male and
female self-injury rates on college campuses.
15
Similarly notable was the strong connection between NSSI and sexual orientation.
Although the general trend is consistent with previous studies,
11,20
finding an interaction
between sexual orientation and sex is novel. In addition to showing other than heterosexual
Sex differences in NSSI in a college population 13
women at much greater risk for NSSI when compared to heterosexual women, results showed
that women in all sexual orientation categories are significantly more likely to report NSSI than
their male counterparts. Although the relationship between sexual orientation and suicide is well
documented, gay males rather than females are typically found to be at elevated risk.
33
This
provides additional evidence that the risk factors for suicide and NSSI may differ. More research
is needed to replicate and explain our finding that sexual orientation was a risk factor for NSSI
among females but not males.
Significant differences with regard to NSSI form help to explain the common conception
that NSSI is a largely female behavior. Females were more likely to endorse scratching and
cutting while males were more likely to endorse punching objects with the overt intention of
hurting oneself. In correspondence with this, females were more likely than males to report
wrists, arms, and thighs as the dominant wound location while males are significantly more
likely to report hands as a primary wound location. These differences may explain why NSSI is
so commonly identified as a female behavior since cutting arms and wrists is the prototypical
form.
1,2,31
Male-preferred forms of NSSI tend to present clinically as outward focused aggression
and may mask self-injurious intent
Consistent with other recent studies,
5
close to a quarter of the NSSI sample (22.6%)
indicated that nobody knew about their self-injury, and among those who had attended therapy
for any reason only 16.9% actually disclosed NSSI to a health practitioner. Females were twice
as likely as males to be in therapy but not to disclose NSSI once there. These findings raise a
number of concerns regarding assessment of NSSI as well as the need to understand more about
reluctance to disclose NSSI.
Sex differences in NSSI in a college population 14
Collectively, our results suggest that treatment interventions for NSSI may need to be
tailored by sex. Consistent with prior findings
28,34,35
most respondents reported NSSI as a means
of regulating affect, although females were more likely than males to endorse this reason for
NSSI. Females were also more likely than males to endorse self-punishment and experiencing an
uncontrollable urge as a reason for NSSI. Conversely, males were more likely than females to
endorse sensation seeking as a primary NSSI function. Males were also more likely than females
to report initiating and engaging in NSSI during states of anger and while under the influence of
drugs or alcohol. They were also more likely than females to engage in NSSI in a social context.
This pattern of findings suggests that while both sexes would benefit from intervention s aimed
at improving emotion regulation, females may benefit from intervention aimed at enhancing self-
concept and esteem while males may benefit from those including impulse and anger control
components.
Although this study constitutes the largest US study conducted to date on NSSI within a
college population it has some limitations. First, the response rate, while typical of web-based
surveys,
36
was not high enough to rule out unknown bias. Second, although drawn from a diverse
set of colleges, the colleges were neither randomly selected nor representative of the US college
population as a whole. Similarly, our findings may not generalize to the non-college population
of persons in this age group or to younger cohorts (although it is important to note that much of
the NSSI data provided reflected behaviors in the secondary school years). Lastly, it is possible
that non-college bound youth may be at higher risk for NSSI since studies have shown that self-
harm that includes suicide attempts is more prevalent in those with less educational achievement
and lower socioeconomic status.
8,37
Sex differences in NSSI in a college population 15
Given the strong links between NSSI behavior to other adverse behaviors and
conditions,
11,23 ,35
individuals in community-based settings, such as schools and youth-serving
organizations are in an unique position to recognize signs of NSSI, thereby facilitating early
mental health referrals. Findings also suggest that males should be routinely screened by health
and mental health care providers for NSSI and that NSSI assessment should include questions
about NSSI.
Sex differences in NSSI in a college population 16
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Sex differences in NSSI in a college population 19
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Sex differences in NSSI in a college population 20
Table 1 Characteristics of Study Participants and Logistic Regression of Male and Female Self-Injury
on Primary Demographic Characteristic
a
No (%)
Odds Ratio (95% CI)
Characteristic
Total
(n=11,529)
No-NSSI
Sample
(n=9,733)
NSSI Sample
(n=1,776)
Univariate
Model
Multivariate
Model
b
Sex
Male
4809 (41.7)
4287 (44.0)
522 (29.4)
1.0
1.0
Female
6639 (57.6)
5385 (55.3)
1254 (70.6)
1.9
c
(1.7-2.1)
1.8
c
(1.6-2.0)
Age
18-20
6705 (58.2)
5879 (60.4)
1046 (58.9)
1.0
1.0
21-25
4824 (41.8)
3854 (39.6)
730 (41.1)
1.0 (0.9-1.1)
1.0 (0.9-1.2)
International student status
Domestic 10436 (90.5) 8761 (90.0) 1655 (93.2) 1.0 1.0
International
954 (8.3)
850 (8.7)
103 (5.8)
0.6
c
(0.5-0.7)
0.7
d
(0.5-0.9)
Race/ethnicity
Non-Hispanic white
7418 (64.3)
6211 (63.8)
1193 (67.2)
1.0
1.0
Asian/Asian American
1764 (15.3)
370 (3.8)
226 (12.7)
0.8
c
(0.6-0.9)
0.8
c
(0.7-0.9)
Sex differences in NSSI in a college population 21
Table 1 (cont) Characteristics of Study Participants and Logistic Regression of Male and Female Self-
Injury on Primary Demographic Characteristic
a
No (%)
Odds Ratio (95% CI)
Characteristic
Total
(n=11,529)
No-NSSI
Sample
(n=9,733)
NSSI
Sample
(n=1,776)
Univariate
Model
Multivariate
Model
b
Hispanic
561 (4.9)
477 (4.9)
83 (4.7)
1.0 (0.7-1.2)
1.0 (0.7-1.3)
African American/
Black
427 (3.7) 1538 (15.8) 57 (3.2) 0.8 (0.6-1.1) 0.8 (0.6-1.2)
Other 1299 (11.3) 1087 (11.2) 210 (11.8) 1.0 (0.8-1.2) 1.0 (0.9-1.2)
Father education
Less than high school 353 (3.1) 303 (3.1) 50 (2.8) 1.0 1.0
High school 1014 (8.8) 847 (8.7) 169 (9.5) 1.2 (0.8-1.7) 1.2 (0.8-1.8)
Some post-high school 1530 (13.3) 1268 (13.0) 265 (14.9) 1.3 (0.9-1.8) 1.4 (1.0-2.0)
College graduate 8416 (74.4) 7134 (73.3) 1293 (72.8) 1.1 (0.8-1.5) 1.2 (0.8-1.6)
Sexual orientation
Heterosexual 8782 (76.1) 7743 (79.6) 1028 (57.9) 1.0 1.0
Mostly straight 1665 (14.4) 1213 (12.5) 447 (25.2) 2.8
c
(2.5-3.2) 2.6
c
(2.2-2.9)
Bisexual 497 (4.3) 309 (3.2) 186 (10.5) 4.0
c
(3.3-4.9) 3.8
c
(3.1-4.6)
Sex differences in NSSI in a college population 22
NSSI = Non-suicidal self-injury
a
Derived from multivariate logistic regression analysis with all demographic characteristics above entered
as predictors of dichotomously coded NSSI. Univariate and multivariate models reported as odds ratios
and confidence intervals (CI).
b
All effects were adjusted simultaneously for sex, international student status, age, race/ethnicity, father
education status, and sexual orientation.
c
P<.001.
d
P<.01.
Table 1 (cont) Characteristics of Study Participants and Logistic Regression of Male and Female Self-
Injury on Primary Demographic Characteristic
a
No (%)
Odds Ratio (95% CI)
Characteristic
Total
(n=11,529)
No-NSSI
Sample
(n=9,733)
NSSI Sample
(n=1,776)
Univariate
Model
Multivariate
Model
b
Mostly gay/lesbian 152 (1.3) 113 (1.2) 39 (2.2) 2.1
c
(1.4-3.1) 2.3
c
(1.6-3.5)
Gay/lesbian 267 (2.3) 227 (2.3) 41 (2.3) 1.3 (0.9-1.9) 1.7
c
(1.1-2.5)
Sex differences in NSSI in a college population 23
NSSI = Non-suicidal self-injury
Table 2 Logistic Regression of Male and Female Self-Injury on Primary NSSI Characteristics
a
No. (%) or Mean (SD)
Odds Ratio (95% CI)
Characteristic
Total
(n=1776)
Female
(n=1254)
Male
(n=522)
Multivariate Model
b
Lifetime frequency
Once
236 (13.3)
159 (12.6)
82 (15.6)
1.0
2-5 times
775 (43.6)
530 (42.3)
245 (46.9)
1.1 (0.7-1.5)
6-10 times
240 (13.5)
155 (12.4)
85 (16.4)
0.8 (0.5-1.3)
11-20 times
197 (11.1)
152 (12.1)
45 (8.7)
1.7 (0.9-2.8)
Over 20 times
324 (18.2)
259 (20.7)
65 (12.5)
1.7
e
(1.1-2.8)
Age of onset
15.2 (0.12)
15.2 (0.13)
15.3 (0.28)
1.0 (0.8-1.2)
Dominant form
c
Scratch
906 (51.0)
728 (58.1)
178 (34.1)
2.5
e
(1.9-3.2)
Cut
698 (39.3)
572 (45.6)
126 (24.1)
2.7
d
(2.1-3.5)
Banged or punched objects
466 (26.2)
237 (18.9)
229 (43.9)
0.3
d
(0.2-0.4)
Punched or banged oneself
288 (14.5)
193 (15.4)
95 (18.2)
0.8 (0.5-1.0)
Bitten self
303 (17.0)
211 (16.2)
92 (17.6)
0.8 (0.6-1.1)
Carved words or symbols
209 (11.7)
154 (12.3)
55 (10.5)
1.1 (0.7-1.6)
Mean number of forms used
2.4 (.05)
2.5 (.07)
2.3 (0.9)
1.1 (0.9-1.2)
f
Sex differences in NSSI in a college population 24
a
Derived from multivariate logistic regression analysis with primary NSSI characteristics entered as
predictors of dichotomously coded NSSI. All multivariate models were conducted with sexual
orientation, international student status, and ethnicity held constant. CI denotes confidence interval.
b
Base = Males.
c
Respondents could select more than one so proportions will total greater than 100%.
d
P <.001.
e
P<.01.
f
Reported as a factor change in the number of events (exp(B))
Sex differences in NSSI in a college population 25
Table 3 Logistic Regression of Male and Female Self-Injury on Secondary NSSI Characteristics and
Help-Seeking
a
No. (%)
Odds Ratio
Characteristic
c
Total
(n=1776)
Female
(n=1254)
Male
(n=522)
Multivariate Model
b
Function
Regulate negative affect
(80.9)
(83.1)
(75.4)
1.6
e
(1.2-2.2)
Control
(35.9)
(40.8)
(23.8)
1.8
e
(1.3-2.6)
Self-punishment
(24.7)
(24.5)
(24.9)
.8 (.6-1.0)
Physiological stimulation
(24.1)
(22.6)
(27.7)
.6
f
(0.5-.8)
Solicit social response
(21.7)
(23.5)
(17.2)
1.2 (0.9-1.6)
Overwhelming urge
(16.9)
(18.8)
(12.2)
1.4
g
(1.1-2.0)
Primary body parts affected
Arm
882 (48.1)
658 (52.5)
224 (42.9)
1.5
f
(1.2-1.9)
Wrist
587 (33.0)
497 (39.7)
90 (17.2)
3.8
e
(2.8-5.1)
Hands
586 (32.9)
360 (29.0)
226 (44.2)
0.5
e
(0.4 -0.6)
Thigh
399 (22.4)
327 (26.1)
72 (13.7)
2.1
e
(1.5- 2.9)
Stomach
257 (14.4)
194 (15.7)
63 (12.3)
1.2 (0.9-1.7)
Calves/ankle
242 (13.6)
209 (16.9)
33 (6.5)
3.6
e
(2.3-5.5)
Finger
192 (10.8)
132 (10.6)
60 (11.7)
0.8 (0.6-1.2)
Sex differences in NSSI in a college population 26
Table 3 (cont) Logistic Regression of Male and Female Self-Injury on Secondary NSSI Characteristics
and Help-Seeking
a
No. (%)
Odds Ratio
Characteristic
c
Total
(n=1776)
Female
(n=1254)
Male
(n=522)
Multivariate Model
b
Initial motivation
Upset and decided to try it
658 (37.0)
513 (40.9)
145 (27.8)
1.6
e
(1.3-2.1)
Angry at self
644 (36.2)
435 (34.7)
209 (40.0)
0.8 (0.7-1.1)
Accidentally discovered it
322 (18.1)
244 (19.5)
78 (14.9)
1.4 (0.9-1.9)
Angry at someone else
301 (17.0)
192 (15.3)
109 (20.9)
0.6
e
(0.4-0.8)
So someone would notice
183 (10.3)
149 (11.9)
34 (6.5)
1.6
g
(1.1-2.7)
To shock or hurt someone
83 (4.7)
66 (5.3)
17 (3.3)
1.2 (0.6-2.2)
Because of being drunk or high
77 (4.3)
30 (2.4)
47 (9.0)
0.2
e
(0.1-.4)
Routines and habits
Always injures in private
1131 (63.7)
879 (70.1)
252 (48.2)
2.5
e
(1.9-3.2)
Does not feel much pain when injuring
468 (26.3)
356 (28.4)
112 (21.5)
1.3 (0.9-1.7)
Experiences phases of high and low
self-injury activity
332 (18.7)
272 (21.7)
60 (11.5)
2.1
e
(1.5-3.1)
Sometimes injures while under the
influence of drugs and/or alcohol
328 (18.4)
187 (14.9)
141 (27.1)
0.4
f
(0.3 - 0.7)
Sex differences in NSSI in a college population 27
Table 3 (cont) Logistic Regression of Male and Female Self-Injury on Secondary NSSI Characteristics
and Help-Seeking
a
No. (%)
Odds Ratio
Characteristic
c
Total
(n=1776)
Female
(n=1254)
Male
(n=522)
Multivariate Model
b
Has friends who self-injure
310 (17.5)
247 (19.7)
63 (12.1)
1.4
g
(1.1-2.1)
Prefers to be in a particular room or
Place
182 (10.2)
149 (11.9)
33 (6.3)
1.8
f
(1.2-2.9)
Sometimes injures in the presence of
Others
186 (8.8)
94 (7.5)
64 (12.3)
0.4
f
(0.3-0.6)
Follows a regular routine
118 (6.6)
96 (7.7)
22 (4.2)
1.6 (0.9-2.8)
Has injured another as part of a self-
injury routine
69 (3.9)
35 (2.8)
34 (6.5)
0.2
e
(0.1-0.5)
Sometimes lets others cause injuries
58 (3.7)
31 (2.5)
27 (5.2)
0.3
e
(0.1-0.5)
Perceived dependency
d
Is difficult to control the urge to self-
Injure
448 (25.2)
345 (27.5)
103 (19.7)
1.9
e
(1.3-2.7)
Believes self-injury is a problem in
his/her life
655 (36.9)
500 (39.9)
155 (29.6)
1.9
e
(1.4-2.6)
Unintended severity
Hurt more severely than expected
351 (20.0)
240 (19.2)
114 (21.9)
0.6
e
(0.5-0.9)
Sex differences in NSSI in a college population 28
Table 3 (cont) Description of Secondary NSSI Characteristics and Help-Seeking by Sex*
No. (%)
Odds Ratio
Characteristic
c
Total
(n=1776)
Female
(n=1254)
Male
(n=522)
Multivariate Model
b
Of those hurt more severely than
intended (n=351), under the
influence of drugs or alcohol when
injury occurred
71 (20.2)
41 (17.1)
30 (26.3)
0.5
e
(0.3-0.9)
Have inured self so badly should have
been seen by a medical professional
139 (7.8)
95 (7.6)
44 (8.4)
1.9 (0.6-1.5)
Have sought medical treatment for
injuries caused
89 (5.0)
70 (5.6)
19 (3.6)
2.2
e
(1.1-4.4)
Disclosure and help-seeking
No one knows about self-injury
Practices
403 (22.6)
266 (21.2)
137 (26.2)
1.1 (0.7-1.8)
Has been to therapy for any reason
941 (52.3)
724 (57.7)
217 (41.6)
2.0
e
(1.6-2.6)
Of those who have been to therapy for
any reason (n=941), has discussed
self-injury with mental health
professional
159 (16.9)
158 (16.8)
160 (17.0)
0.9 (0.5-1.8)
NSSI = Non-suicidal self-injury
a
Derived from multivariate logistic regression analysis with secondary NSSI characteristics entered as
predictors of dichotomously coded NSSI. All multivariate models were conducted with sexual
orientation, international student status and ethnicity held constant. CI denotes confidence interval.
Sex differences in NSSI in a college population 29
b
Base = Males.
c
Respondents could select more than one so proportions will total greater than 100%.
d
Sum of subgroup numbers may not be equal to total N as a result of missing data.
e
P<.001.
f
P<.01.
g
P<.05.
