This study aimed to further explore the recent conceptualisation of depression and suicidality as related yet independent constructs. Our findings revealed that approximately one-third of individuals with lifetime suicide attempts and over one-third of individuals with lifetime suicidal ideation did not have a history of depressive disorder, providing support for the emerging theory of these conditions as separable states. This concurs with previous research conducted in an urban Australian population [5
], which found strong evidence for depression and suicidality as independent constructs. This indicates a similarity in psychological mechanisms across geographical areas. On a univariate basis, lifetime depressive disorder was strongly related to suicidal ideation and suicide attempts, producing approximately a six-fold increase in the likelihood of an individual experiencing either of these phenomena.
Importantly, all of our participants who met diagnostic criteria for lifetime depression did so even when the DSM-IV suicidality item (item 9) was removed. Therefore the association observed between depression and suicidal ideation was not solely attributable to the inclusion of suicidal ideation in the symptom criteria for depressive disorder. However we acknowledge that the CIDI focuses on the participants’ most severe lifetime depressive episode, which is likely to explain this finding. That is, as the CIDI focuses on the episode for which the most symptoms were endorsed, removing one of these symptoms may not have had as great an impact on meeting diagnostic criteria as it would have when focusing on a less severe episode.
In both univariate and multivariate analyses, depression was the strongest predictor of suicidal ideation. However, in addition to depressive disorder, a variety of other factors were associated with thoughts of suicide. Significant multivariate effects were observed for both PTSD and anxiety disorder, while being unmarried was also associated with an increased likelihood of experiencing lifetime suicidal ideation. Marital status serves as an important proxy for social support, and our findings emphasise the moderating role of interpersonal relationships for individuals who may be at risk of suicide despite having no depressive history. Therefore, programs aimed to enhance social support among rural communities may be an effective public health approach for the reduction of rural suicide. The finding that younger participants were more likely to endorse lifetime suicidal ideation and attempts has been observed in previous Australian community-based research, both for suicidality [33
], and for other psychological conditions such as depression, anxiety, and alcohol use [34
]. This suggests that there may be a cohort effect, in that psychological conditions may be becoming increasingly common in younger generations, or this may be a survivor effect. Alternatively this may be due to a bias in lifetime recall, since older participants may be less likely to remember suicidal thoughts and behaviours if they occurred many years ago. Consistent with previous evidence [19
], we also detected a small proportion of individuals experiencing suicidal ideation in the absence of any psychiatric diagnosis. Indicators of the clinical severity of suicidality (e.g. age at first suicidal thoughts and attempt, number and severity of suicide attempts) did not differ among participants with or without a lifetime diagnosis of depression.
When data were back-weighted to match the entire ARMHS sample, our results for suicidal ideation remained largely unchanged. The back-weighted data continued to support the finding that additional demographic factors and psychological diagnoses may contribute to suicide risk when depression is accounted for.
While a strong univariate relationship was observed between depression and lifetime suicide attempts, the multivariate association was weaker, and reached only marginal significance. Unlike suicidal ideation, depression was not the strongest correlate of lifetime suicide attempts on either a univariate or multivariate basis. This indicates an important additional role of secondary psychiatric diagnoses.
Both lifetime drug use and anxiety disorders showed a strong relationship with lifetime suicide attempts, and are important risk factors. There was also a significant interaction for suicide attempts between depression and PTSD; among individuals with depression, a comorbid diagnosis of PTSD greatly increased the odds of a suicide attempt. An increased awareness of the additional potential for suicidal behaviours among this group is warranted. These results were replicated even when data were back-weighted, indicating that these findings may be applicable to larger populations, and were not skewed by our over-representation of people with elevated psychological distress.
Our ROC analyses revealed that depression alone is somewhat limited in its predictive power for both suicidal ideation and suicide attempts. Our analysis indicated the necessity to assess a wider range of psychological conditions in evaluating suicidality.
The main implications of these findings are likely to apply in treatment settings. At present, the consideration of suicidality primarily as a product of a depressive episode has resulted in it frequently being treated as such. During assessments by clinicians, if no evidence is found for the primary symptoms of depression, assessment of “secondary” symptoms such as suicidality may not be undertaken [6
], and therefore these individuals may not be referred for further treatment. Clinicians may feel less equipped to assist individuals who experience thoughts of suicide independently of a depressive illness. Where diagnostic criteria for depression are met, suicidality is generally considered as just one factor contributing to an overall diagnosis, and may not be highlighted as a focus of concern above other, less severe, symptoms [6
]. Considering recent findings that suicidality and depression may be relatively independent constructs [5
], the assumption that treating the overall depressive state extends to effective treatment of individual symptoms such as suicidality may be somewhat unfounded. In particular, people presenting with comorbid psychiatric conditions (especially PTSD) may require integrated treatments for these conditions in order for their suicide risk to be reduced [36
]. Our findings highlight the potential need to consider different risk factors for individuals depending on their depressive history and personal circumstances.
The present research is limited by low participant numbers, which may have restricted our power to detect effects, particularly for the interactions. Due to the restricted sample size, it is possible that the present study underestimates characteristics that may distinguish between individuals who experience suicidality within and outside of the context of a depressive episode. Similarly, we had insufficient numbers of participants with a psychotic disorder to include this as a predictor, despite the likely impact of this condition [15
]. Our sample was entirely non-metropolitan, and therefore is not representative of urban residents. Our analyses focused primarily on lifetime diagnoses of psychiatric disorders, which have been found to be subject to inaccuracy of recall [37
], therefore our findings may be biased towards the null. Additionally, the use of lifetime diagnoses did not allow us to determine whether depression preceded suicidality in participants who experienced both of these conditions. It is possible that among participants who met criteria for both depression and suicidal thoughts or behaviours during their lifetime, the suicidality may still have occurred in the absence of a depressive episode. Future research utilising a larger sample may enable collection of sufficient data to focus on 12-month diagnoses, which may be of greater relevance. By assuming that participants without suicidal ideation also did not have a lifetime suicide attempt, impulsive attempts were not able to be detected in our analysis. Therefore it is likely that this study underestimates the total number of suicide attempts, and overstates the contribution of depression to such attempts. This may be addressed in future by using a less structured assessment which allows for the exploration of suicide attempts among individuals with no history of ideation. Future research may also benefit from the inclusion of a measure of impulsivity, as this is likely to contribute to suicide attempts among individuals experiencing suicidal ideation [38