Ires Ghielen

170 Chapter 9 their lives. Practical suggestions for improvement in the BEWARE study, both for the treatment and study design, resulted from qualitative assessments in which patient researchers from the Dutch Parkinson Patient Association (Parkinson Vereniging) performed interviews with the participating patients. We incorporated these suggestions to improve the BEWARE treatment and our study design. To date, the BEWARE study is the only RCT that investigated a treatment for anxiety in PD patients and is anxiety still considered to be an ignored but important aspect of PD [19]. Because of the co-occurrence of motor and mental symptoms, we recommend treating anxiety in PD in a multidisciplinary manner, increasing effectiveness using a holistic approach. In this way, we can break through the vicious cycle of subsequent motor and anxiety symptoms. For PD patients that experience wearing-off related anxiety, one can imagine this makes the wearing-off experience less stressful and increases psychological wellbeing [6]. Methodological considerations The methodological strengths and limitations were discussed in each individual chapter. Here we summarize and further discuss important strengths and limitations of the research in this thesis. A major strength of this thesis is the use of different statistical techniques that together provide important insights in the complex relationships between motor and non-motor symptoms, mainly anxiety, in PD. The different symptom dimensions of anxiety were first investigated in a large patient sample ( chapter 2 ) and were replicated in a patient sample with considerable neuropsychiatric symptoms ( chapter 3 ), which improves the generalizability of our findings. Cross-sectional associations were investigated in large patient samples ( chapters 2, 3, and 4 ) using principal component analyses and network analysis, from which we gained insights in these associations on the level of anxiety dimensions and on single symptom-level. The principal component analyses address the shared variation amongst symptoms, while the network analysis shows unique symptom-to-symptom variations within different patient groups [38]. The longitudinal study design in chapter 5 allowed us to draw conclusions regarding temporal relationships and the influence of possible confounders between motor and anxiety symptoms in PD. Another major strength of this thesis is that we investigated the first multidisciplinary treatment combining ACT and physical therapy using an RCT design ( chapters 7 and 8 ). Moreover, it is the first and only RCT investigating a treatment for anxiety in PD to date. In this RCT, we collaborated closely with patient researchers of the Dutch Parkinson Patient