• AAQ-II
• Experiential Avoidance
• longitudinal study
• negative affectivity
• predictive role
• Psychological Flexibility

Psychological Flexibility is the core psychological construct of Acceptance and Commitment Therapy (ACT) and Relational Frame Theory (RFT). Over the last years an increasing and promising body of research has suggested that Psychological Flexibility may play a key role in the maintenance of Psychological Well-being and in the prevention of the development of psychosocial problems. Unfortunately, the most widely used instrument to assess Psychological Flexibility, the Acceptance and Action Questionnaire (AAQ), has never been validated in Italian, and thus its use in the Italian population is only partially legitimated. Moreover, the vast majority of observational studies carried out on the RFT/ACT psychopathological model are cross-sectional in nature. At the moment, only one observational longitudinal study has explored the predictive role of Psychological Flexibility in a general population sample. Yet this kind of studies is extremely important, being one of the best methodological instruments to assess whether a psychological construct can be considered a vulnerability factor. For these reasons the first aim of the present thesis was to validate the AAQ-II in Italian and to explore its psychometric properties. The second aim of the thesis was to explore, by means of a longitudinal design with one-year follow-up performed in a general population sample, the predictive role of Psychological Flexibility on various outcome measures and the effects of the interaction of Psychological Flexibility with age on the levels of Depression and Anxiety.
The Italian validation of the AAQ-II was conducted on a sample of 255 University students and their relatives and friends. Results of the Principal Component Analysis suggested a single factor solution as the best one to fit the data. The internal consistency and the temporal stability at one year were good. Higher AAQ-II scores were found to be associated with lower levels of psychopathology and higher levels of Eudaimonic Well-being. Moreover, higher AAQ-II scores were associated with lower levels of Experiential Avoidance, Thought Suppression, Anxiety Sensitivity, Trait Anxiety, and Alexithymia, and with higher levels of Mindfulness. The AAQ-II remained significantly associated with Depression, Anxiety, and Eudaimonic Well-being after controlling for Experiential Avoidance, Thought Suppression, Anxiety Sensitivity, Trait Anxiety, Alexithymia, and Mindfulness, thus confirming that Psychological Flexibility is something that goes beyond these conceptually related constructs.
Results of the series of hierarchical regression analyses, performed in order to evaluate the predictive role of Psychological Flexibility, showed that basal levels of AAQ-II were able to predict the levels of Anxiety, Depression, Social Anxiety, Relations with self and others, and Daily living and Role functioning skills at one year follow up, even when the basal levels of Anxiety and/or Depression and the basal level of the outcome measure were controlled. Psychological Flexibility accounted for 10-17% of the variance in follow-up levels of the outcome measures. Results thus support the belief that a lack of Psychological Flexibility represents a broad vulnerability factor for the development of psychopathology and the reduction of Quality of Life.
Finally, as far as follow-up Depression levels are concerned, an interaction effect between age and AAQ-II was observed, suggesting that age could moderate the effects of Psychological Flexibility on Depression levels one year later.