Motivation for Psychiatric Treatment in Outpatients with Severe Mental Illness

The main aim of the current thesis was to empirically test and compare three current theoretical models of motivation for treatment in the context of outpatient psychiatric care for patients with severe mental illness (SMI). In a literature review (Chapter 2), we argued that Self-Determination Theory (SDT)64, the TransTheoretical Model (TTM)44 and the Integral Model of Treatment Motivation (IM)37 provided unique yet complementary frameworks that could be useful as the basis for health care interventions in outpatients with SMI. A cluster randomised controlled trial was designed (Chapter 3) to test whether a Motivation Feedback intervention was effective at improving treatment engagement and outcomes, and data from the trial were used to empirically test the three motivation theories. As the testing of theories is founded on the proper assessment of theoretical constructs, assessment methods were first investigated. Using structural equation modelling, assessment instruments from SDT were found to be valid and reliable (Chapter 4). Subsequently, support was found for the hypotheses from SDT and the model was found to be stable across time and different diagnostic patient groups, and was able to explain 18% to 36% of variance in clinical outcomes (i.e. treatment engagement, psychosocial functioning and quality of life) (Chapter 5). Similar empirical tests were performed to evaluate the applicability of the IM (Chapter 6) and the TTM (Chapter 7). Although the assessment of motivation was found to be reliable for the IM, the basic hypotheses from IM were not supported, nor was the model similar across time and patient groups. The IM constructs did explain between 22% and 86% of variance in clinical outcomes, depending on the timing of the assessment. Regarding the TTM, two different assessment methods for the stages of change were found to show low convergence and partially showed the expected associations with other TTM constructs and with treatment engagement. The TTM stages of change explained 3% to 16% of variance in clinical outcomes. Regarding the trial, it was expected that Motivation Feedback (MF) based on SDT, which was provided additional to treatment as usual (TAU), would induce more awareness regarding motivation for treatment and aid the internalization of the patient’s motivation resulting in a higher level of treatment engagement, compared to TAU only. After one year of treatment, however, no differences between the intervention group and control group on treatment engagement, psychosocial functioning and quality of life were found (Chapter 8). An evaluation of internal validity, including nonresponse bias, information bias, implementation issues and differential effects between patients with psychotic disorders and personality disorders, largely explained why MF was not able to improve outcomes. Finally, it was found that the accuracy by which clinicians were able to estimate patient ratings of motivation ranged from low to moderate (Chapter 9). It is concluded that a negotiated approach on motivation is needed, yet the use of Motivation Feedback is insufficient to improve motivation and treatment engagement in patients with SMI.