Acceptance-Based and Traditional Cognitive-Behavioural Stress Management in the Workplace: Investigating the Mediators and Moderators of Change

This thesis describes three intervention studies that were designed to investigate the mediators and moderators of change in worksite stress management training (SMT) programmes. In the first study (Study I), 154 local government employees were randomly assigned to one of three conditions: 1) a training programme based on acceptance and commitment therapy (ACT); 2) stress inoculation training (SIT); or 3) a waist-list control group. The ACT and SIT interventions were delivered to small groups of employees via three training sessions spread over three months. Outcome and process of change measures were administered at baseline (Time 1), three months after two sessions of training (Time 2), and again in three months after a final session of training (Time 3). Both ACT and Sit resulted in large improvements in general mental health across the six month assessment period. Further analyses indicated that the beneficial impact of ACT on mental health was mediated by an increase in psychological flexibility, while the impact of SIT was mediated (at least in part) by a decrease in dysfunctional cognitions. Study II used a similar methodology to investigate the impact of ACT on the frequency of dysfunctional thinking, and on learning at work. In this second study, 81 local government employees were randomly assigned to an ACT group or to a wait-list control group. The ACT intervention resulted in a significant improvement in employee well-being across a seven month period. As predicted, these improvements mental health were mediated by an increase in psychological flexibility but not by a reduction in the frequency of dysfunctional thinking. Psychological flexibility also served as the mechanism by which ACT increased work-related learning. In the final study (Study III), participants’ initial level strain was examined as a potential moderator of change in the ACT and SIT interventions. The data from the two previous studies were merged for this final analysis. Results indicated that initial level of strain moderated the effects of these two interventions on employees’ mental health. Moreover, approximately 70% of the initially high strain ACT and SIT participants improved to a clinically significant degree by the final assessment point. The general discussion focuses on the theoretical and practical implications of this research, and highlights the utility of using worksite SMT programmes to test underlying cognitive-behavioural theories of change