Irritability: an investigation of prevalence and clinical correlates in adolescence and adulthood

Irritability is a mood that most people experience as part of a normal, healthy life. It is also a symptom or associated feature of a number of psychological disorders. There is a general belief that adolescents experience irritability to a greater degree than other age groups and high levels of irritability during adolescence are independently predictive of suicide risk and the development of internalising disorders. Irritability research has however been hampered by a lack of appropriate measures, to address this issue Stringaris et al. (2012) created the Affective Reactivity Index which has been shown to be a reliable and valid measure of irritability in adolescents in both the US and UK. Irritability is a psychological symptom that is thought to be developmentally sensitive. For example, in the DSM-5 irritability is a symptom of depressive disorders for children and adolescents but not for adults. Yet little research has been conducted examining the developmental trajectory of irritability, and no peer reviewed publications were found that compared irritability in the context of depressive disorders or other depressive symptoms between adolescence and adulthood. The present thesis, prepared as a thesis by publication, aimed to determine whether the ARI was a psychometrically sound tool for use with Australian adults and adolescents. The thesis used the ARI to investigate the associations irritability has with mental health problems, as well as any differences in irritability or its associations with mental health problems between adults and adolescents. The first paper entitled ‘Psychometric properties of the Affective Reactivity Index in Australian adults and adolescents’ has been resubmitted to Psychological Assessment after reviewer’s comments were addressed. This paper reports that the ARI is a reliable measure in both Australian adults (α = 0.80) and adolescents (α = 0.85). The measure conforms to the single factor structure proposed by Stringaris et al. (2012), although there may be some item redundancy. The validation analyses are promising with moderate correlations between the ARI and measures of psychopathology, demonstrating convergent validity. The second paper entitled ‘Irritability and psychopathology: A comparison between adolescents and adults’ has been submitted to The Australian and New Zealand Journal of Psychiatry. This paper directly compares the level of irritability and the association irritability has with depressive symptoms between adolescents and adults. Adults had higher mean irritability scores than adolescents and also higher mean depressive symptom scores. Adults who reported they experienced impairment due to their irritability were more likely to score above the clinical cut off on measures of depression and anxiety. Irritability was strongly associated with depressive symptoms in both adults and adolescents, and with anxiety symptoms in adults. The results reported in this paper indicate that the belief that adolescents are more irritable than adults may not be true, though adolescents may be more prone to experiencing impairing irritability in the absence of categorical mental health disorders than adults. Additionally there was little difference in the level of association between irritability and depressive symptoms between adolescents and adults indicating the need for further research to determine if irritability is also a salient feature of adult depressive disorders. The third paper entitled ‘Can irritability act as a marker of psychopathology?’ is under review by Journal of Adolescence. This paper examines how irritability differs between a community sample of adolescents and a clinical sample of adolescents diagnosed with psychological disorders. As expected the clinical sample reported significantly higher mean irritability scores than the community sample. The clinical sample also had a greater degree of impairment associated with their irritability than the community sample. A receiver operating characteristic (ROC) analysis found that according to self report a score of 4 on the ARI was the optimum cut off point for distinguishing between those with and without a DSM-IV diagnosis. This value resulted in an area under the curve of 0.86 (95% CI 0.76 to 0.95) with a sensitivity of 77.4% and a specificity of 77.4%. The data reported in this paper demonstrates that irritability is strongly associated with mental health problems in adolescents and due to this it may be possible to use the ARI as a screen for psychological disorder. The results presented in this thesis call into question the widely held belief that adolescents are more irritable than adults. However, the adult sample comprised mostly young adults so any conclusions drawn can only be made in terms of young adults. The results presented here also provide initial evidence that the relationship between irritability and depression may continue into adulthood. These results cannot be extrapolated to the entirety of adulthood but for young adults at least, irritability may continue to be a relevant symptom of depressive disorders.