Development and validation of the illness perceptions questionnaire for youth anxiety and depression (IPQ-Anxiety and IPQ-Depression)

Background: The Revised Illness Perceptions Questionnaire (IPQ-R) is a well-established measure for measuring illness representations with sound psychometric properties. However, one limitation is that it provides a generic measure of illness representations and lacks specificity to individual health conditions, making it difficult to capture the nuances of illness beliefs for different populations. Objective: The aim of this study was to develop reliable and valid versions of the IPQ-R for young people with anxiety and depression to better understand how they perceive and cognitively represent the course, severity, impact, and treatability of their anxiety and depression. Methods: This mixed-methods study consisted of a qualitative study, involving semi-structured interviews (n = 26) followed by think-aloud interviews (n = 13), and a quantitative study (n = 349), resulting in the development of the IPQ-Anxiety (IPQ-A) and IPQ-Depression (IPQ-D). Item development is reported, along with the psychometric properties of the measures. Concurrent validity was assessed by correlating the IPQ-A and IPQ-D with the Brief Illness Perceptions Questionnaire (B-IPQ) across equivalent dimensions. Results: Results suggest that the IPQ-A, IPQ-D, B-IPQ-A and B-IPQ-D are valid and reliable tools for measuring mental illness representations. The measures show acceptable model fit, high factor loadings, and good to excellent internal consistency, test – retest reliability across subscales and concurrent validity with mental health measures. Conclusions: The development of these measures represents an important step in the field of youth mental health by providing the opportunity for reliable assessment of young people’s conceptualisations of their anxiety and depression. Better understanding of young people’s illness beliefs has the potential to open a range of intervention possibilities by prioritising illness perceptions over the supposed objective condition severity and trajectory