Experiential Avoidance as a Transdiagnostic Mediator in the Relationship Between Intolerance of Uncertainty, Maladaptive Perfectionism, and Psychiatric Symptoms: Structural and Causal Mediation Analyses in a Clinical Sample.

Anxiety- and depression-related disorders rank among the most prevalent psychological conditions globally. Intolerance of uncertainty (IU), perfectionism, and experiential avoidance (EA) are recognized as transdiagnostic factors contributing to the development and maintenance of these emotional disturbances. However, their interplay remains insufficiently understood and has not been examined within a single research design across clinical samples with varying psychiatric diagnoses. Investigating the relationships and clinical significance of these key transdiagnostic processes in the maintenance of psychiatric symptoms represents a research priority. This study examined the mediating role of EA in the relationship between IU, maladaptive perfectionism (MP), and psychiatric symptoms (PS) using structural equation modeling (SEM) and causal mediation analyses. The sample included 221 participants (18-65 years) with a range of anxiety- and depression-related diagnoses. SEM results showed that EA fully mediated the relationships between IU, MP, and PS. Increased IU and MP were linked to heightened EA, which, in turn, was associated with greater symptom severity. The model explained 54.5% of the variance in EA and 62.5% in PS. Causal mediation analyses showed that EA fully mediated the relationships between IU and PS and MP and PS in two separate models. EA explained 1.254 standard deviations in the IU-PS relationship and 0.871 standard deviations in the MP-PS relationship. Sensitivity analyses (ρ = -0.1) supported the robustness of these effects against potential confounders. These findings underscore the potential utility of assessments and interventions targeting EA to more effectively address the relationship between MP, IU, and anxiety- and depression-related disorders. SUMMARY: This study is among the first to examine the role of EA in the relationship between intolerance of uncertainty (IU), MP, and PS in individuals with anxiety- and depression-related disorders. IU and MP are associated with psychiatric PS severity through EA. Causal mediation analyses confirmed EA as a key mechanism linking IU and MP to PS, with results remaining robust after controlling for potential confounders. Avoidance behaviors appear to contribute to the maintenance and reinforcement of MP traits and IU, as their direct associations with PS were fully mediated by EA, resulting in increased symptom burden. In individuals with anxiety- and depression-related disorders, assessing and addressing avoidance strategies may help reduce symptom burden in those with high IU and MP tendencies.