The interpersonal-psychological theory of suicidal behavior (Joiner, 2005
) proposes that an individual will not die by suicide unless he/she has both the desire and the capability to do so. The theory specifies that suicidal ideation results from the joint presence of two emotionally painful psychological states—low belongingness and perceived burdensomeness—and that acquired capability for suicide results from exposure and attendant habituation to the pain and fear involved in physical self-harm. Results of two studies presented here were consistent with this view.
Study 1 tested the prediction that the interaction of low family support (cf. low belongingness) and low mattering to others (cf. perceived burdensomeness) would predict severity of suicidal ideation. Results were consistent with this prediction and indicated that individuals with low levels of both family support and mattering to others experienced the most severe levels of suicidal ideation. Notably, both six-month and lifetime histories of depression were included as covariates, indicating that the theory’s variables predicted suicidal ideation above and beyond the contribution of depression. These findings, consistent with the theory, suggest that when people hold two psychological states in their minds simultaneously—low belongingness and perceived burdensomeness—dangerous forms of suicidal ideation are likely to emerge.
Results of Study 1 (i.e., a significant interaction between indices of low belonging and perceived burdensomeness in the prediction of suicidal ideation) are consistent with previous findings (Van Orden et al., 2008
) and build upon these findings due to strengths of the current study’s sample and methods. Strengths of Study 1 include: 1) the use of an ethnically diverse sample, which supports the generalizability of the results; 2) the covariance of lifetime and six-month histories of major depressive disorder, which supports the specificity of the results (i.e., results are not merely due to depression); 3) the use of scales to measure low belongingness and perceived burdensomeness designed by research groups other than our own (i.e., effects are not dependent on the Interpersonal Needs Questionnaire used by Van Orden et al., 2008
), which supports the construct validity of our results.
Study 2 tested the linchpin hypothesis of the interpersonal-psychological theory, namely, that the outcome of lethal or near-lethal suicidal behavior depends on the joint presence of low belongingness, perceived burdensomeness, and acquired capability for suicide. Results were in line with predictions and indicated that the three-way interaction of low belongingness, perceived burdensomeness, and levels of acquired capability (measured by number of past suicide attempts) predicted whether or not participants’ suicidal crises involved suicide attempts versus suicidal ideation. Results indicated that the combination of high levels of both failed belongingness and perceived burdensomeness was most likely to translate into suicide attempts in the presence of higher levels of acquired capability (indicated by greater numbers of past attempts). Results were obtained above and beyond the contribution of numerous documented risk factors for suicidal behavior, including depression, hopelessness, and borderline personality disorder features. In line with the theory, these results suggest that individuals experiencing both low belongingness and perceived burdensomeness are most likely to act on suicidal ideation (i.e., attempt suicide) in the presence of the acquired capability to overcome self-preservation motives and to engage in suicidal behavior.
Interestingly, in a recent study conducted by Huth-Bocks, Kerr, Ivey, Kramer, and King (2007)
, the SPS outperformed measures of suicidal ideation, depression, and hopelessness (namely, the Suicidal Ideation Questionnaire-Junior, Reynolds Adolescent Depression Scale, and Beck Hopelessness Scale) in predicting future suicidal ideation and attempts in a sample of hospitalized adolescents. According to Huth-Bocks and colleagues, this may be because the SPS assesses a broad range of constructs theoretically related to suicidality. We would suggest, given the present findings and in light of the interpersonal-psychological theory, the roles of belonging and burdensomeness, in particular, might be the key constructs being assessed that may partially account for the SPS's strong predictive validity.
Strengths of Study 2 include the use of a sample with severe suicidal symptoms and a dependent measure that allowed for a rigorous test of the theory (i.e., differentiating between severe suicidal ideation/planning and suicide attempts). Results of Study 2 are consistent with previous findings (Van Orden et al., 2008
) and extend previous findings by including all three components of the theory (i.e., low belonging, perceived burdensomeness, and acquired capability). This is the first study to test the three-way interaction between all three components of the theory and to include suicide attempts as an outcome; thus, the current study represents the most rigorous test thus far of the hypothesis that serious suicidal behavior (i.e., lethal or near lethal suicide attempts) is more likely when an individual simultaneously experiences failed belongingness, perceived burdensomeness, and acquired capability for lethal self-injury. Given the difficulty in predicting suicidal behavior due to the low base rates of non-lethal and lethal suicide attempts, theoretical advances that allow for the generation of increasingly precise predictions are especially useful. Results of the current studies suggest that the interpersonal-psychological theory represents one such theoretical advance, as it may improve the field’s precision in the prediction of suicidal behavior.
The current studies, while consistent with the interpersonal-psychological theory, were limited by several factors that suggest directions for future research. As stated above, all of our results are cross-sectional, which was also a limitation of the Van Orden et al. (2008)
studies. The interpersonal-psychological theory specifically predicts that acquired capability, perceived burdensomeness, and low belongingness are all jointly necessary and sufficient proximal causes
of serious suicidal behavior. Although the current study does provide evidence of these constructs as non-spurious correlates of suicidal behavior (i.e., we controlled for key variables, such as depressive symptoms, family history of suicide, other mood disorders, etc.), the case for causality is weakened without evidence for temporal precedence. Our results provide a firm foundation for future work that aims to examine this three-way interaction longitudinally.
Another limitation is our use of proxy variables for some of the constructs (e.g., past attempts for acquired capability). For the current studies, we did not have access to measures specifically designed to assess the interpersonal-psychological theory’s constructs. However, as mentioned above, results conformed to predictions using measures other than the Interpersonal Needs Questionnaire (Van Orden et al., 2008
) and the Acquired Capability Scale (Van Orden et al., 2008
), indicating that previous findings are not specific to measures designed by our laboratory and thereby supporting the construct validity of the theory. However, our use of past suicide attempts as an indicator of acquired capability in Study 2 warrants attention as a direction for future research. The interpersonal-psychological theory specifies that acquired capability for lethal self-injury is the proposed mechanism for the documented link between past and future suicidal behavior (e.g., Joiner et al., 2005
). As such, the number of past attempts is not a “pure” measure of acquired capability, although it remains a potent predictor of the presence of the acquired capability. This stems from the proposition that, according to the theory, there exists a plethora of possible pathways that may increase the level of acquired capability for suicide—past suicide attempts is just one. Furthermore, even within the domain of suicide attempts alone, not all attempts will have an equal effect on the level acquired capacity, given that suicide attempts will vary on important parameters such as intent, means, and severity of outcome. Future research is needed to disentangle the complex relations between suicide attempts, acquired capacity, and future episodes of suicidal behavior.
Relatedly, Study 2 was also limited by the lack of information available on prior combat exposure, which, in conjunction with past suicide attempts, might have resulted in a better approximation of the level of acquired capability in the sample. Indeed, according to the theory, combat exposure would certainly be a potential source for habituating to painful and provocative experiences and, consequently, acquiring the capability to enact lethal self-injury. Given its salience to acquired capability, future studies using similar populations to examine this construct should include measures of prior experiences in combat.
An additional limitation—and direction for future research—involves our examination of non-lethal suicidal behavior (i.e., attempts, ideation) rather than death by suicide. The interpersonal-psychological theory, unlike many other theories of suicidal behavior, is unique in that it attempts to differentiate individuals likely to engage in lethal or near-lethal suicide attempts from those who desire suicide or make low-lethality attempts. Thus, the ultimate goal of this theory is to prevent death by suicide by determining more sensitive and specific predictors of it. Studies examining failed belongingness, perceived burdensomeness, acquired capability, and death by suicide are needed to fully test the theory.
A final limitation involves relatively small effect sizes. Although our effect sizes are, in some cases, small, our results conformed to stringent, a priori hypotheses, persisted after controlling for numerous, clinically relevant variables, and were similar in some cases to effects for variables with traditionally strong effects.
In closing, we consider clinical implications of our findings as well as future directions for research on clinical applications of the interpersonal-psychological theory. Results of Study 2—that the three-way interaction of low belonging, perceived burdensomeness, and acquired capability significantly predicted suicide attempt status—suggest that it would be advisable for clinicians to be cognizant of their patients’ levels of belongingness, burdensomeness, and acquired capability (especially previous suicide attempts), as this knowledge may aid clinicians in the task of suicide risk assessment. Regarding low belongingness, clinicians should assess the degree to which patients feel connected to—and cared about—by others, being especially alert for instances in which belonging is completely absent. Patients can be asked if they have someone to call when they are upset, if they live alone, how often they see friends, etc. Regarding perceived burdensomeness, clinicians can pose the following to patients: “Sometimes my patients tell me they think, ‘the people in my life would be better off I was gone.’ Do you ever think that?” To further assess these two constructs clinicians may wish to administer questions from the Suicide Probability Scale (Cull & Gill, 1988
), which was used to assess levels of burdensomeness and belongingness in Study 2, or the Interpersonal Needs Questionnaire (Van Orden et al., 2008
We suggested above that studies demonstrating the temporal precedence of low belongingness, perceived burdensomeness, and acquired capability are needed to corroborate the hypothesis of the theory that these constructs are proximal causes of serious suicidal behavior. A clinically relevant method to examine temporal precedence involves examining mechanisms of change in therapeutic interventions for suicidal behavior. For example, studies could examine the hypothesis that targeting low belongingness and perceived burdensomeness in therapy will lead to reductions in suicidal ideation. Such interventions could use a cognitive therapy approach; for example, targeting the potentially fatal cognitive distortion, “my death will be worth more than my life to family, friends, society, etc.” (cf., perceived burdensomeness). Interventions could also take a behavioral approach and encourage suicidal patients to engage in activities likely to foster social connections as well as activities that involve helping others (Linehan’s 
Dialectical Behavior Therapy Skills Training Manual lists 176 pleasant activities that are helpful in this regard). If reductions in suicidal ideation following these interventions are found to be due to alleviations in low belongingness and perceived burdensomeness, these findings would support the causal role of the theory’s constructs, as well as the utility of addressing these constructs in interventions for suicidal behavior.
In support of these clinical applications of the theory, the only intervention that has been shown in a randomized controlled trial to be effective in preventing deaths by suicide is an outreach intervention that involved mailing letters expressing concern to high-risk individuals who refused further treatment after hospitalization (Motto & Bostrom, 2001
). Although not directly tested by Motto and Bostrom (2001)
, it may well be that increasing belongingness is the mechanism whereby the intervention prevented deaths by suicide; indeed, it was Motto and Bostrom’s view that this was so. Our results regarding the interactive nature of the theory are consistent with the (potentially) life-saving role of increasing belongingness in this intervention and suggest that altering even just one of the three constructs (i.e., low belonging, perceived burdensomeness, or acquired capability) may substantially reduce risk for suicide.