Ires Ghielen

171 General discussion Association (Parkinson Vereniging) which enabled us to systematically involve the patients to further improve the BEWARE training. Nonetheless, there are some methodological limitations that are important to discuss. First of all, the BAI was used in three of our studies, in which we investigated the cross-sectional associations ( chapters 2 through 4 ). The BAI is considered not the most reliable measure of anxiety in PD patients, since it contains mainly items measuring episodic forms of anxiety, disregarding non-episodic forms of anxiety such as generalized anxiety disorder, which is the most common anxiety disorder in PD [39, 40]. For future research, it is therefore recommended to use, for example, the Parkinson Anxiety Scale (PAS) developed by Leentjens and colleagues [41], which includes items referring to both episodic and non-episodic forms of anxiety. Also, it includes avoidance behaviours, which is an important part of anxiety [8]. In chapter 5 we used the Hospital Anxiety and Depression Scale to assess anxiety symptoms on multiple time points to investigate longitudinal relationships. Measurements were three weeks apart, which did not allow us to investigate the motor – anxiety interactions over shorter periods of time (e.g. minutes or hours), which might be more interesting in PD patients with fluctuations. In addition, the questionnaires that were used inquired about symptoms over different time periods, e.g. one versus four weeks, which resulted in average scores over different time periods and refrained us from drawing causal conclusions about symptom interactions. The associations investigated in chapters 2 through 5 showed that motor and anxiety symptoms can co-occur, however, the interactions might be better investigated using time-series data in which symptom measurements are performed in much shorter time intervals (e.g. multiple times a day) using, for example, expierence sampling method. Regarding anxiety diagnoses, the diagnosis that patients received in chapter 3 was not assessed through a structural clinical interview, but through psychiatric evaluation in daily clinical practice. Although the primary diagnosis was correctly reported, secondary diagnoses of anxiety might not always have been reported, mainly in cases with a primary psychiatric disorder that could also explain the present anxiety symptoms (e.g. psychotic disorder, parkinson’s disease dementia). A structured interview might have resulted in more secondary anxiety diagnoses. Unfortunately, in the PD patient sample used in chapter 4 , data on psychiatric diagnoses were not available to divide our patient group on whether or not patients had an anxiety disorder. We divided the patient group into high- versus low-anxious 9