Introduction
Occupational adaptation (OA) is a dynamic and ongoing process through which individuals modifies their participation in meaningful activities to address challenges arising from changes in their abilities, environments, or life circumstances [1]. This adaptive process holds particular significance for individuals living in chronic and progressive conditions, such as Parkinson’s disease (PD). Parkinson’s disease is a neurodegenerative disorder characterized by both motor and non-motor symptoms, presenting persistent challenges that can profoundly affect an individual’s ability to develop OA [2, 3].
Promoting OA is essential because it empowers individuals to preserve their independence by improving participation and well-being through continued engagement in meaningful daily activities.
The occupational adaptation model highlights relative mastery as a primary indicator of OA, including effectiveness, efficiency, and satisfaction [1]. The relative mastery scale (RMS) is a validated instrument for measuring relative mastery. It employed a 5-point Likert scale in conjunction with open-ended questions focusing on selected occupations [4]. The application of RMS enables clinicians and researchers to comprehensively understand an individual’s adaptive response to occupational challenges.
Literature proposes a longitudinal relationship between sleep quality, depression, and fatigue in the PD population. Zhou et al. reported that PD patients with fatigue exhibit more motor and non-motor symptoms (i.e. sleep, depression, and cognitive impairment) [5]. Moreover, psychological factors, such as depression and apathy, share a linear worsening trajectory [6, 7]. Patients with depression experience substantial disease progression, cognitive decline, and restricted participation in activities of daily living for 12 months [8]. Furthermore, a substantial increase in the fear of falling over longitudinal follow-up leads to difficulties in occupational participation [9]. 
This study investigated psychological predictors of OA in individuals with PD. We hypothesized that specific prevalent demographic and psychological symptoms in PD patients, which are most related to their quality of life, are predictors of OA scores [10-13]. Therefore, we hypothesized that some demographic and prevalent clinical variables in PD would serve as predictors of OA scores. By identifying these predictive elements, this study aimed to provide valuable insights that can inform targeted interventions, ultimately supporting OA and enhancing the participation of those living with PD.

Materials and Methods
A convenient non-probability sampling method was employed to recruit 100 individuals diagnosed with PD from neurological outpatient centers in Tehran City, Iran. The inclusion criteria included a diagnosis based on the UK Brain Bank criteria [14], demonstrating no significant cognitive impairments (as assessed by a Montreal cognitive assessment score over 24) [15], and possessing proficiency in reading and writing in Persian. The exclusion criteria included individuals with comorbid neurological conditions, and participants were given the option to withdraw from the study at any time if they expressed reluctance to continue participating.

Procedure
Demographic characteristics, including age, sex, time since PD diagnosis, Levodopa equivalent daily dose (referring to the dosing schedule) [16], Hoehn and Yahr staging scale, and living arrangements, were assessed by an occupational therapist, with breaks offered as needed. The Lille apathy rating scale (LARS) was administered. Other surveys were provided to participants in a packet, including the RMS, hospital anxiety and depression scale-depression subscale (HADS-D), Tilburg frailty indicator (TFI), Pittsburgh sleep quality index (PSQI), falls efficacy scale-international (FES-I), fatigue severity scale (FSS), and Parkinson disease questionnaire-39 (PDQ-39).
Patients were required to complete the questionnaires in their “ON” state, 1 h after levodopa intake. Participants were given 48 to 72 h to complete the questionnaires and were encouraged to highlight any concerns. At the subsequent meeting for survey collection, we addressed any issues that arose and ensured clarity and completion of all questionnaire sections.

Assessments
The relative mastery scale (RMS) was developed to assess the concept of OA in occupational activities chosen by clients. It comprises six items, each rated on a scale ranging from -2 to +2. The cumulative score on this scale ranges from -12 to +12, with higher scores indicating more significant OA. In addition to these items, the scale included three open-ended questions on performance in the selected occupational activity. The validity and reliability of the scale have been established, with a reported Cronbach’s α value of 0.94 [17]. The translation of the RMS into Persian has been completed for caregivers of patients with multiple sclerosis [18]. The research team assessed this test’s reliability in people with PD, and Cronbach’s α was 0.87. However, these results have not been reported.
The Lille apathy rating scale (LARS) measures apathy with a semi-structured interview in nine domains. The total score ranges from -15 to +15, with higher scores indicating a higher level of apathy. The minimal clinically important difference (MCID) was 2.99 points. The LARS has been validated in a PD population and used in Persian populations [7, 19].
The hospital anxiety and depression scale-depression subscale (HADS-D) measures depression and anxiety with two 7-item subscales. Each item is scored from 0 (no problem) to 3 (severe problem). The MCID for depression subscale score of this scale was 1.7 points. This scale has been extensively used in the PD population and has a Cronbach’s α (0.86, for the depression subscale) in Persian [20, 21]. 
The Tilburg frailty indicator (TFI) is a self-report questionnaire designed to measure frailty in older adults. It consists of 15 items that assess three domains: Physical, psychological, and social. Each item is scored on a 3-point scale (0=no problem to 2=severe problem). The MCID for the total score on this scale is one point. The TFI demonstrated good reliability in patients with PD and acceptable psychometric properties in Persian patients [22, 23].
The Pittsburgh sleep quality index (PSQI) evaluates sleep quality with 24 items. Items are scored from zero to three, with higher scores indicating poorer subjective sleep quality. The MCID for this scale is three points. Farrahi Moghaddam et al. reported 0.78 of Cronbach’s α for this scale in healthy people [24]. 
The falls efficacy scale-international (FES-I) evaluates fall concerns in various physical and social activities with 16 items. Items are rated on a 4-point Likert scale (1=not concerned; 4=very concerned). The total score ranged from 16 to 64, with higher scores denoting a higher fear of falling. The MCID for the total score on this scale was four points. Psychometric properties were evaluated in patients with PD, and Cronbach’s α for the Persian version was 0.94 [25, 26].
The fatigue severity scale (FSS) measures the severity of fatigue and its effect on daily life activities. This scale consists of nine items, ranging from 1 (strongly disagree) to 7 (strongly agree). The total score was calculated by summing the item scores divided by nine. Higher scores reflect higher fatigue levels. The MCID for this scale was 0.45. This scale has been used in the PD population and has an interclass correlation (ICC) of 0.93 in Iranian people [27, 28].
The Parkinson disease questionnaire-39 (PDQ-39) is a tool designed to measure the quality of life in individuals with PD. It assesses how the disease impacts daily living and well-being. The PDQ-39 includes 39 items divided into eight dimensions: Mobility, activities of daily living, emotional well-being, stigma, social support, cognition, communication, and bodily discomfort. The total score ranged from 0 to 100, with higher scores indicating worse conditions. The MCID of the total score was 1.6. This questionnaire showed acceptable validation properties in Iranian with PD [29].

Statistical analysis
The Shapiro-Wilk test was applied to evaluate the normal distribution, and descriptive statistics were used to summarize demographic and clinical characteristics. Statistical significance was set at 0.05. A stepwise regression model was employed, using correlated demographic and clinical variables (Hoehn and Yahr stages, disease duration, apathy, frailty, fatigue, fall concern, sleep quality, quality of life, and depression) as independent variables and the RMS total score as the dependent variable. All the variables were included simultaneously in the regression equation.

Results
A total of 100 individuals diagnosed with PD participated in this study. The participants had a mean age of 60.23 years, with a standard deviation of 9.27 years. The average duration of the disease since diagnosis was 7.66 years, accompanied by a standard deviation of 5.19 years. Table 1 presents detailed demographic information.




The RMS exhibited a significant (P<0.05) moderate correlation with PDQ-39 (P=-0.42), hospital anxiety and depression scale-depression subscale (HADS-D) (P=-0.37), TFI (P=-0.42), FESI (P=-0.37), and Pittsburgh sleep quality index (PSQI) (P=-0.32). Additionally, a weak correlation was observed with LARS (P=-0.29), disease duration (P=-0.20), and H and Y stage (P=-0.29). No significant correlation was observed between RMS and other explored demographic variables.
A comprehensive standard multiple regression analysis was conducted to predict OA using RMS scores. Various demographic and clinical variables were simultaneously included in the model to ensure a thorough examination of contributing factors. The analysis revealed a significant model, explaining 29.7% of the variance in RMS scores. It indicated that quality of life, frailty, apathy, and sleep quality were significant predictors of the total RMS score (P<0.05). Table 2 presents the results of the stepwise analysis.




These results highlight the multifaceted nature of occupational adaptation in individuals with PD and the importance of addressing these critical factors in clinical practice. The practical implications of these findings are substantial, and advocate a more comprehensive approach to patient care.

Discussion
Occupational adaptation is a learning process that enables individuals to develop, modify, or acquire the skills necessary to remain engaged in their desired occupations [1]. This process is particularly crucial for those dealing with chronic conditions or disabilities, such as PD. Given the essential role of OA in rehabilitation and ongoing management of PD as a degenerative condition, the ability to predict the state of OA is crucial. This study found that quality of life, frailty, apathy, and sleep quality were the leading factors that predicted relative mastery.
Stepwise regression analysis revealed that quality of life, frailty, apathy, and sleep quality were the most significant predictors of the RMS total score among patients with PD. Quality of life, the strongest predictor of OA, is a multidimensional construct encompassing various aspects of an individual’s life. These aspects include physical, psychological, and social components, and subjective life satisfaction [24]. OA involves interaction between people, their environments, and their occupations. As a comprehensive concept, quality of life incorporates all these elements.
In the context of frailty, higher levels of perceived mastery can empower older adults to better cope with their health challenges, potentially mitigating the adverse effects of frailty. Studies have indicated that older adults who perceive themselves as having more excellent mastery report better quality of life and resilience to challenges associated with frailty [25].
Apathy was another significant predictor RM. This often results in feelings of disconnection and decreases motivation for goal-directed behaviors. Individuals with apathy may not pay close attention to the outcomes of their actions or lack the desire to learn from their experiences [13]. Conversely, engaging in daily activities is essential to develop a sense of mastery in life. Since apathy typically manifests as a lack of interest or motivation to participate in these activities, fostering a sense of mastery may encourage individuals to become more involved and address their symptoms of apathy.
Poor sleep quality is a prevalent symptom of PD, which may be due to disruption of sleep-regulating pathways in this population [26]. Previous studies have demonstrated a strong correlation between poor sleep quality and disruptions in advanced cognitive processes, directly impacting the essential sub-processes for learning and fostering mastery in these individuals [27, 28].

Conclusion
The results of this study have significant implications for assessing and managing occupational adaptation in individuals with PD. This research underscores the importance of quality of life, frailty, apathy, and sleep quality as critical predictors of occupational adaptation, with quality of life emerging as the most influential factor. This understanding equips healthcare professionals, researchers, and students with knowledge of the key elements that influence occupational adaptation and their role in applying it in their work. These results have the potential to influence the field significantly, inspiring the development of more effective interventions and strategies, thereby advancing the field and improving the well-being of patients with PD.
This study has several significant limitations. First, convenience sampling was used. While this approach allowed for the inclusion of a diverse range of participants, it also meant that the study selected readily available participants, which may limit how well the results apply to all patients with PD.
This study’s focus on individuals with good cognitive health is a significant limitation. This approach may exclude patients with cognitive decline, a common feature of PD, potentially leading to findings that do not fully represent the population with PD. Furthermore, the limited number of participants in advanced stages of the disease, a crucial group for a comprehensive understanding of PD, is an area that future research should address. Another issue that warrants attention is the nearly equal gender distribution among participants. Given that PD is more prevalent in men, this could introduce a bias in the findings. Moreover, higher levels of apathy experienced by men could potentially reduce their participation. This sex imbalance underscores the need for further research to validate the conclusions in the entire population affected by PD.

Ethical Considerations

Compliance with ethical guidelines
This study was approved by the Ethics Committee of Iran University of Medical Sciences, Tehran, Iran (Code: IR.IUMS.REC.1402.101). Participants signed a form to provide informed consent. Each participant was assigned a unique code to ensure privacy and anonymity during the research.

Funding
This article extracted from the master thesis of Jafar Haj Ghani, approved by Iran University of Medical Sciences, Tehran, Iran.

Authors' contributions
Conceptualization and supervision: Ghorban Taghizadeh, Akram Azad, Seyed Amir Hasan Habibi; Data analysis: Ghorban Taghizadeh; Sample recruitment, data collection, writing article: Jafar Haj Ghani.

Conflict of interest
The authors declared no conflict of interest.

Acknowledgments
The authors would like to acknowledge Iran University of Medical Science for providing the facilities and resources necessary for this research.



References