Assessment of Self-Injurious Thoughts Using a Behavioral Test

The participants were 89 (68 female) adolescents with a mean age of 17.10 years (SD=1.92, range=12–19) who identified themselves as European American (73.0%), African American (3.4%), Hispanic (6.7%), Asian American (11.2%), or having mixed or other ethnicity (5.6%). The participants included those with a recent (past year) history of nonsuicidal self-injury (N=53) and a noninjurious comparison group (N=36). This group size provided strong statistical power (0.96) to detect the large between-group differences (d=0.80, alpha=0.05, two-tailed) required for the Self-Injury Implicit Association Test to be a useful clinical tool. Participants were recruited through announcements posted in psychiatric clinics, newspapers, community bulletin boards, and the Internet. All procedures were approved by Harvard University’s institutional review board. Written informed consent was obtained for all participants, with parental consent for those less than 18 years old.

All of the assessments were completed during one session in a behavioral research laboratory. We examined two versions of the Self-Injury Implicit Association Test: one that measures how strongly individuals associate self-injury with themselves (the identity version) and one that measures the automatic association of self-injury with evaluative positivity (the attitude version). The two versions were developed, administered, and scored according to standard procedures for the Implicit Association Test (3) . Briefly, each participant was seated alone at a desktop computer and instructed to classify stimuli that appeared in the center of the computer screen as quickly as possible by pressing two keys: “e” for stimuli to be classified on the left of the screen and “i” for stimuli classified on the right.

The identity version of the Self-Injury Implicit Association Test tested the strength of the association an individual holds between self-injury and him- or herself. The participants were presented with a series of images that were either related to self-injury (i.e., pictures of skin that had been cut) or neutral (i.e., pictures of noninjured skin) and were asked to classify these as quickly as possible as representing the concept “Cutting” or “No Cutting.” We intentionally focused only on cutting to limit variability in the experimental procedures and because prior work indicates that cutting is the primary method of nonsuicidal self-injury (9) . Of the current 53 self-injurers, 51 (96.2%) reported using cutting, among other methods, for self-injury. In the identity version of the test, participants also were presented with words that were either self-relevant (e.g., “I,” “Mine”) or other-relevant (e.g., “They,” “Them”) and were asked to classify these as quickly as possible as representing the attributes “Me” or “Not Me.” Correct classifications were followed by presentation of the next stimulus, and incorrect classifications were followed by presentation of a red “X,” which remained until the correct key press was made.

For the first critical test block (presented in random order) the participants were instructed to press the same computer key in response to both “Cutting” and “Me” stimuli (thus pairing stimuli related to self-injury and oneself) and the other computer key for “No Cutting” and “Not Me” stimuli ( Figure 1 ). For the second critical test block, the opposite sorting was performed (i.e., pairing stimuli related to noninjuring and oneself). Response latencies in these two blocks were recorded and analyzed by using a standard Implicit Association Test scoring algorithm (3) . The relative strength of the association between self-injury and oneself was indexed by calculating a standardized D score for each participant by subtracting the mean response latency for the Cutting/Me test block from the mean response latency of the Cutting/Not Me test block and dividing by the standard deviation of the response latency for all trials. Thus, positive D scores reflect faster responding (i.e., stronger associations) when self-injury and oneself are paired, whereas negative D scores reflect slower responding (i.e., weaker associations) when self-injury and oneself are paired.

Our second form of the test, the attitude version, followed the same procedures but used the categories of “Good” (e.g., “Pleasure,” “Relief”) and “Bad” (e.g., “Painful,” “Ineffective”) instead of the categories of “Me” and “Not Me.”

Demographic factors including age, sex, and race/ethnicity were assessed in face-to-face interviews. To ensure that between-group differences on the Self-Injury Implicit Association Test were not due to differences in IQ, all participants also were assessed with the Wechsler Abbreviated Scale of Intelligence (10) . Psychiatric disorders are associated with nonsuicidal self-injury (11, 12), and therefore they were assessed by using the Schedule for Affective Disorders and Schizophrenia for School-Age Children—Present and Lifetime Version (K-SADS-PL) (13) . Given their associations with self-injury, we focused specifically on disorders of mood (major depression, bipolar disorder), anxiety (panic, separation anxiety, phobias, generalized anxiety, and obsessive-compulsive disorder), impulse control (oppositional defiant, conduct, and attention deficit hyperactivity disorder), eating (bulimia nervosa, anorexia nervosa), and substance use (alcohol, drugs). Level of clinical severity was measured by using the Children’s Global Assessment Scale (14) . The presence of nonsuicidal self-injury in the past year was assessed by using the Self-Injurious Thoughts and Behaviors Interview, a structured interview with strong interrater reliability, test-retest reliability, and construct validity (Nock et al., unpublished manuscript, 2006).

Performance results on the two versions of the Self-Injury Implicit Association Test (i.e., D scores) for the two groups were compared by using t tests. The ability of the instruments to add incrementally to the prediction of nonsuicidal self-injury was tested by using two separate hierarchical logistic regression analyses (one for each test version) in which demographic factors (age, gender, race/ethnicity) were entered in the first step, psychiatric factors (full-scale IQ, presence of each class of disorder, total number of disorders, and score on the Children’s Global Assessment Scale) were entered in the second step, and D scores were entered in the third step.

Analyses revealed large and statistically significant differences between the self-injurers and noninjurers on the identity version of the Self-Injury Implicit Association Test ( Figure 2 ). As presented on the left side of the figure, those engaging in nonsuicidal self-injury showed a positive association (D score) between “Cutting” and “Me” (mean=0.18, SD=0.45), while the noninjurers showed a negative association (mean=–0.31, SD=0.34). Analyses also revealed a large and statistically significant difference on the attitude version of the test. As presented on the right side of Figure 2, both groups showed a positive association between “Cutting” and “Bad,” but the association was significantly stronger for the noninjurers (mean=–0.53, SD=0.29) than for those engaging in self-injury (mean=–0.16, SD=0.41).

In terms of incremental predictive validity, after accounting for the variance explained by the demographic (χ ² =6.00, df=3, R ² =0.09, p=0.12) and psychiatric (χ ² =38.66, df=8, ΔR ² =0.44, p<0.001) factors, we found that performance on both the identity version (χ ² =10.38, df=1, ΔR ² =0.18, p=0.001) and attitude version (χ ² =4.74, df=1, ΔR ² =0.14, p=0.03) of the Self-Injury Implicit Association Test independently and significantly improved the statistical prediction of nonsuicidal self-injury. Notably, scores on the two versions were correlated (r=0.50, N=89, p<0.001), and when entered simultaneously in the third step of the regression equation, the identity version continued to significantly predict self-injury (odds ratio=11.32, p=0.02), whereas the attitude form of the test did not (odds ratio=2.87, p=0.31).

The Self-Injury Implicit Association Test uses individuals’ response times to measure the implicit associations they hold about self-injury. Our results revealed remarkable group differences between self-injurers and noninjurers, supporting the criterion validity of this measure. Moreover, performance on two versions of this test significantly improved the statistical prediction of nonsuicidal self-injury beyond the use of demographic and psychiatric factors, suggesting that the test holds promise for improving the detection and prediction of self-injurious behaviors. This initial study introduces a novel method of assessing the nature of self-injurious thoughts that does not rely on self-report, which represents a major advance in risk assessment. Future research must demonstrate the prospective, predictive validity of the test before it can be recommended for use in clinical settings. Demonstrating that the Self-Injury Implicit Association Test improves prospective prediction beyond self-report would further highlight the utility of this measure. Future research also should test the usefulness of implicit measures for assessing other sensitive and/or stigmatized clinical behaviors, as well as the use of such measures for examining mechanisms of change during treatment (15) .

Received Sept. 14, 2006; revision received Oct. 17, 2006; accepted Nov. 17, 2006. From the Department of Psychology, Harvard University. Address correspondence and reprint requests to Dr. Nock, Department of Psychology, Harvard University, 33 Kirkland St., Cambridge, MA 02138; [email protected] (e-mail).

Both authors report no competing interests.

Supported by NIMH grants MH-076047 (Dr. Nock) and MH-57672 (Dr. Banaji) and by grants from the Milton Fund and Talley Fund of Harvard University (Dr. Nock).

The authors thank members of the Laboratory for Clinical and Developmental Research and Roy Ruhling for their assistance with this work.