Skip to main content
Journal of Patient-Reported Outcomes
Download PDF

Evaluation and validation of a patient-reported quality-of-life questionnaire for Parkinson’s disease

Journal of Patient-Reported Outcomes volume 6, Article number: 17 (2022) Cite this article

Abstract

Background

Parkinson’s disease (PD) is a chronic, progressive illness with a profound impact on the health-related quality of life (HRQoL). Disease-specific patient-reported HRQoL measures, such as PDQ-39 and its short version PDQ-8, are increasingly used in clinical practice to address the consequences of PD on everyday life. Due to limitations in the content, especially in non-motor symptoms and sleep disturbances of PDQ-8, PDQoL7, a 7-item, short-term, self-reported, PD-specific HRQoL questionnaire was developed.

Methods

A representative sample of 60 adults with idiopathic PD completed the PDQoL7 questionnaire and the existing validated PDQ-8 and EQ-5D-5L questionnaires (all in Greek).

Results

PDQoL7 summary index strongly correlated with PDQ-8 (rs = 0.833, P < 0.001) and EQ-5D-5L (rs =  − 0.852, P < 0.001). The correlation between PDQoL7 and EQ-5D-5L was statistically significantly stronger compared to PDQ-8 and EQ-5D-5L (rs =  − 0.852 vs rs =  − 0.789 respectively, P < 0.001). The internal consistency of PDQoL7 was not affected by item deletion (positive item to total correlations: 0.29–0.63). No redundant items (with inter-item correlation coefficients greater than 0.80) were identified. Cronbach’s α for PDQoL7 was comparable to PDQ-8 (0.804 versus 0.799 respectively). As PDQoL7 had three-dimensional structure, omega coefficient analysis confirmed its reliability (omega total: 0.88; omega hierarchical: 0.58).

Conclusions

PDQoL7 is an acceptable, easy to use, valid and reliable tool for the determination of HRQoL in PD patients that is potentially more comprehensive than PDQ-8 based on the available evidence. PDQoL7 could allow for a more thorough evaluation of the impact of PD and contribute to guiding healthcare decisions. This will be confirmed in subsequent analysis on larger patient cohorts.

Introduction

Health-related quality-of-life (HRQoL) is a broad multidimensional concept that reflects the subjective perceptions of patients on the impact of their disease on physical, mental, emotional, and social functioning and overall well-being [1, 2]. Self-reported HRQoL-tools, both generic and disease-specific, were developed over the last decades and are increasingly used as outcomes in clinical studies of chronic diseases both to quantify the burden of the disease on the patients’ everyday life, the impact of treatment and guide health policy decisions [3, 4]. HRQoL assessments are of clinical value provided that they fulfil certain requirements [5]. These include valid theoretical basis (construct validity), content validity, reproducibility, acceptability by respondents, clarity, cultural validity, inter-relatedness of items to allow for the determination of the same underlying construct (internal consistency), ability to detect changes over time in the measured construct (responsiveness), unidimensionality and in the context of clinical trials practicability and ease of use [5].

Parkinson’s disease (PD) is a chronic, progressive neurodegenerative disease that severely affects the HRQoL of patients compared to healthy controls [6]. The correlates of poor HRQoL in PD patients are multifactorial and include demographics (such as age and gender), PD clinical characteristics (such as severity of motor and non-motor symptoms, PD subtypes, disease duration), adverse effects of treatment, comorbid conditions, and psychosocial function [7,8,9]. Both generic and PD-specific HRQoL tools have been used in PD patients [3, 6, 10,11,12,13]. Among the currently available PD-specific HRQoL tools, the Parkinson’s disease questionnaire-39 item (PDQ-39) that contains 39 items that are grouped under 8 domains, and its shorter version PDQ-8 that contains 8 items, each representing a domain of the PDQ-39 are more widely used [10, 14,15,16,17]. PDQ-8 can be used as part of the original PDQ-39 questionnaire (nested) or independently [18]. Due to is brevity, PDQ-8 requires less time to complete, but has lower reliability and validity compared to PDQ-39 [12, 19,20,21]. Despite their broad use, a major limitation of PDQ-39 and PDQ-8 is the lack of clarity in some items that could lead to misconceptions as well as the lack of items on most non-motor symptoms [10, 12]. However, non-motor symptoms can have a detrimental impact on PD prognosis and the overall health status of the patients that exceeds that of motor symptoms [22,23,24,25,26,27,28]. Non-motor symptoms, such as night sleep problems, drooling, fatigue, urination problems and dizziness are independent predictors of poor QoL [11, 25, 29]. They are, however, not included in PDQ-8 items. For instance, sleep disorders stand out among non-motor symptoms, given their high prevalence and severe impact on cognitive function and HRQoL [28, 30,31,32,33]. Ιncreasing evidence suggests that sleep problems and non-motor symptom burden do not only correlate with HRQoL assessments, but can also be predictive of longitudinal ΗΡQoL change in PD patients [6, 23, 24, 34,35,36,37]. In addition, poor sleep quality in PD is associated with depression, anxiety and advanced disease [36]. Another disadvantage of the PDQ-8 tool is that the patient should answer every question recalling the last month’s events, impressions, feelings and thoughts, something not so easy taking also in account the possible cognitive impairment of the PD patient.

Thus, the need for a convenient, reliable, with short recall period, easy to answer, clear and comprehensive tool which covers the range of symptoms of PD patients could contribute towards a better HRQoL estimation. The objective of this study is the development of a content-valid PD-specific HRQoL questionnaire, PDQoL7, that maintains some of the features of PDQ-8, such as the ease of use, and contains improvements in item content to assess the impact of PD on physical, mental and social aspects.

Materials and methods

PDQoL7 development

PDQoL7 is a 7-item self-reported PD-specific HRQoL questionnaire that relies on the patient’s perception of their well-being during last week, in 7 discrete domains (one item per domain). The selection of the items that were included in PDQoL7 was based on consultation with healthcare professionals that have experience in PD patients, symptoms spontaneously reported by PD patients during routine visits to healthcare professionals (without being actively asked by healthcare professionals), as well as problems encountered by PD patients due to ambiguity in content or inability to understand some items in the existing PDQ-39/PDQ-8 tools [38]. For example, regarding question 7 of PDQ-8 “Had painful muscle cramps or spasms”, patient’s answer should focus only on the pain-accompanied muscle tone alterations (i.e., painful early morning dystonia), omitting other very common painful conditions that could exist in PD [25, 26]. The selected items that were included in PDQoL7 were also confirmed by literature review [8, 9, 11, 12, 19].

PDQoL7 was developed in Greek language. It has 7 items, each corresponding to a distinct domain with 4 possible scores (0 = never, 1 = rarely, 2 = sometimes; 3 = often, 4 = always), and assesses the frequency with which patients experience difficulties due to PD in: (1) Mobility addresses problems of mobility (difficulties with walking, moving the hands or changing position in bed) (2) Skills & Personal care addresses difficulties with activities such as working, driving, hobbies, housework, personal hygiene and getting dressed. (3) Social Life & Communication addresses perceived support from social relationships, for example, feeling isolated or having problems in communication with close relationships, family, or friends, (4) Problems from non-motor symptoms addresses the most commonly reported non-motor symptoms associated with PD, such as pain, fatigue, sialorrhea, constipation, frequent urination, orthostatic phenomena, (5) Emotional status addresses emotional problems, such as feeling depressed (6) Mental status addresses difficulties with attention or having trouble in maintaining focus and (7) Sleep addresses the presence of sleep problems, night-time sleep problems, or drowsiness during the day. For comparison purposes, the questions of PDQoL7 and PDQ-8 are provided in Additional file 1: Fig. 1).

The validity of PDQoL7 was explored by correlating it to the validated Greek versions of PDQ-8 (PDQ-8Grv) and EQ-5D-5L [21, 39]. Lower scores for both PDQoL7 and PDQ-8 represented a higher HRQoL, whereas the opposite applies for EQ-5D-5L index score (range 0–1) with higher scores indicating higher health utility. PDQ-8 was chosen for comparison purposes because the number of items and time required for completion are comparable to PDQoL7.

Study subjects

This study was conducted in the Outpatient Parkinson’s Disease practice of Mediterraneo Hospital (Athens, Greece). The study received approval from the institution’s scientific committee and all patients provided informed consent. Sixty adult idiopathic PD patients, according to the criteria of the International Parkinson and Movement Disorder Society and the UK Parkinson's Disease Society Brain Bank that did not suffer from dementia or conditions that would interfere with the study’s assessments were consecutively enrolled from June 2019 to December 2019. During a single visit, medical history and records were reviewed, the patients underwent clinical examination, and were instructed to complete PDQoL7, PDQ-8 and EQ-5D-5L QoL. All three questionnaires were completed on the same day within approximately 5 min each and were reviewed by the rater(s) for response clarity and completion. Other routine assessment tools that were completed were the MDS-UPDRS Greek official version, Part I: item 1.1 for cognitive impairment, and 1.3 for depressed mood; Part IV: items 4.1–4.4 (% off and disability due to off and % levodopa-induced dyskinesia-LID, and disability due to LID), and the non-motor questionnaire (NMSQuest) [13, 40, 41]. The collected variables also included PD staging (modified Hoehn and Yahr scale) and PD subtype (based on motor signs and PD onset) [42, 43]. Wearing-off and LID % scores were combined with weights based on the disability due to off-state and the disability due to LID, to create two indexes: Disability-Off and Disability-LID.

Statistical analysis

Categorical variables were presented as absolute (N) and relative frequencies (%) and continuous variables are presented as mean values (standard deviation: SD) and/ or median values (Interquartile Range: IQR, expressed as the 25th–75th percentile of their distribution). Floor and ceiling effects were assessed by means of frequencies. Normality of the continuous characteristics’ distribution was tested through the P-P plots and the Shapiro–Wilk test. The criterion validity (convergent validity) of PDQoL7, i.e., the extent to which it correlates with another tool that measures HRQoL in PD patients, was determined versus the Greek validated versions of the PD-specific PDQ-8 and the generic HRQoL EQ-5D-5L using Spearman’s correlation coefficient (rs) [21, 39]. EQ-5D-5L QoL questionnaire has been validated in PD patients [44]. The EQ-5D-5L is a 5-item questionnaire that measures a related, but different construct to PDQoL7/PDQ-8 by evaluating mobility, self-care, daily activities, pain/discomfort, as well as anxiety/depression on a 5-level Likert scale (no problems, slight problems, moderate problems, severe problems and extreme problems, ranging from 1 to 5 points) [45].

The internal consistency (reliability) and validity of PDQoL7 and PDQ-8 were assessed by Cronbach’s α coefficient and inter-item correlations. Cronbach’s α value > 0.70 was used for group-level comparisons. For item-total correlation each item had to correlate with the total score with r > 0.2 (Pearson’s correlation). Cronbach’s α in the range of 0.70–0.95 was considered as an adequate measure of internal consistency.

The assumption that underpins the summing of rating scale items into a total score is their unidimensionality, i.e., that the items represent a common underlying construct [5, 14]. Exploratory Factor Analysis (EFA) using the extraction method of Principal Components was applied to identify the different components of both instruments (PDQoL7, PDQ-8). The specific methodology has been chosen, as it constitutes one of the standard and most widely used statistical methodologies for demonstrating the construct validity of QoL questionnaires [46,47,48]. To ensure suitability for conducting EFA, we used the Kaiser–Mayer–Olkin (KMO) test and the Bartlett’s test of sphericity. The orthogonal rotation (Varimax method) was used to simplify the factors’ structure and to enhance their interpretability. To determine the number of factors to be kept we used the criteria of eigenvalues > 1.0 and the ‘elbow’ of the scree plot, in addition to the Monte Carlo Parallel analysis, which is an alternative technique that compares the scree plots of factors of the observed data with those of a random data matrix of the same size as the original [49,50,51]. For each factor, component loadings were interpreted using the following cut-offs (non-normal distributions): ≥ 0.5 relevant, ≥ 0.6 good, and ≥ 0.7 very good. It is noted that a sample size of at least 10 observations per item is usually required to obtain reliable high-quality factor analysis results and to avoid computational difficulties, yet as suggested in the literature, a sample size of N = 50 is considered to be a reasonable absolute minimum [52, 53]. For a sample size of 50, a loading of 0.722 was considered significant. Moreover, the omega Hierarchical was also calculated for both scores (PDQoL7 and PDQ-8 scores) so as to estimate their precision in measuring one general/ overall construct.

In addition to the EFA, the hierarchical cluster analysis based on the Ward’s linkage and the squared Euclidean distances was also applied, in order to identify the instruments’ structure and to compare it with components provided by the EFA. Finally, univariable and multivariable linear regression analysis was performed to test the impact of various demographic and clinical characteristics of the patients on the PDQoL7 and PDQ-8 scores. Stepwise multiple regression analysis was used to determine the factors that best accounted for the variance in HRQoL scores.

Results

Demographics and clinical characteristics

The basic demographic and clinical characteristics of the study patients are summarized in Additional file 1: Table 1. Patients of male:female ratio 55:45%, with mean age (± SD) 64.52 ± 9.39 years were enrolled and were equally distributed between akinetic-rigid and tremor-dominant subtypes. Most of the patients were of stage 2–3 (modified Hoehn and Yahr scale) in PD severity (73.4%), had normal cognition or up to mild cognitive impairment and were affected with 1–10 nonmotor symptoms (43.3%). Slight or up to moderate depressed mood was reported by 95% of the subjects.

Descriptive statistics of the scores for each item of PDQoL7 and PDQ8 are shown in Additional file 1: Table 2. The mean (± SD) PDQoL7 and PDQ-8 scores were respectively 14.58 ± 5.55 and 11.82 ± 6.04. There were no missing data. Furthermore, there was no evidence of floor or ceiling effects with only 3.3% and 1.7% of the study patients scoring the lowest value in PDQoL7 (score 4) and PDQ-8 (score 0) respectively, while 1.7% of the patients scored the maximum in either instrument [PDQoL7 (score = 24), PDQ-8 (score = 23)].

Correlation between PDQoL7, PDQ-8 and EQ-5D-5L

PDQoL7 and PDQ-8 were strongly correlated (Spearman’s correlation r = 0.833, P < 0.001). Either tool correlated strongly with PD duration since diagnosis, PD severity, NMSQuest score and MDS-UPDRS-assessed cognitive impairment, disability-Off index, and depressed mood (Table 1). In addition, both scores were significantly and negatively associated with the EQ-5D-5L index score, while it should also be noted that the correlation between the PDQoL7 and the EQ-5D-5L index score (rs = − 0.852; 95% CI = [− 0.909, − 0.794]) was significantly stronger (p < 0.001), when compared to the one between the PDQ-8 and the EQ-5D-5L index score (rs = − 0.789; 95% CI = [− 0.842, − 0.669]).

Table 1 Spearman’s correlation between PDQoL7/PDQ-8 questionnaire scores and demographic/clinical variables
Full size table

Both for PDQoL7 and PDQ-8, no redundant items (with inter-item correlation coefficients greater than 0.80) were identified (Table 2). PDQoL7 and PDQ-8 also had adequate internal consistency (PDQoL7 total Cronbach’s α: 0.804; intraclass correlation coefficient, 95% CI: 0.716–0.872 and PDQ-8 total Cronbach’s α: 0.799; intraclass correlation coefficient, 95% CI: 0.711–0.868). The internal consistency for either of the two questionnaires was not affected by item deletion and the reliability analysis (positive item to total correlations in the range of 0.29–0.63) was satisfactory.

Table 2 Results for reliability analysis for PDQoL7 and PDQ-8
Full size table

The degree of agreement (concordance) in responders’ assessments was low both for PDQoL7 and PDQ-8 (PDQoL7: Kendall’s Coefficient of Concordance W = 0.192, P < 0.001 and for PDQ-8 W = 0.088, P < 0.001).

Principal component factor analysis/hierarchical cluster analysis

The PDQoL7 items seemed to be related and therefore suitable for structure detection via factor analysis (Bartlett’s test of sphericity χ2 = 136.4, P < 0.001). Similar results were obtained for PDQ-8 (χ2 = 162.1, P < 0.001). Three components had eigenvalues greater than 1 accounting collectively for almost 76% of the variance in the PDQoL7 scores (Additional file 1: Table 3). For PDQoL7, component 1 included “Mobility” and “Skills & Personal-care”, component 2 “Social life & Communication” and “Emotional status” and component 3 “Cognition & Sleep”. The omega hierarchical of PDQoL7 was 0.58, while the omega total was 0.88.

For PDQ-8, 2 components accounted for almost 60% of the variance (Additional file 1: Table 4). Component 1 included the items “Mobility”, “Activities of daily living”, “Cognitions”, and “Bodily discomfort”, and component 2 the items “Social support”, “Communication”, and “Stigma”. The item “Emotional well-being” moderately correlated with both components. The omega hierarchical of PDQ-8 tool was 0.51, while the omega total was 0.87.

Hierarchical cluster analysis identified three clusters for PDQoL7 and two clusters for PDQ-8 (Additional file 1: Table 5).

Regression analysis

Univariate regression models demonstrated that the factors which significantly affected the PDQoL7 score were the number of years since diagnosis, PD severity, cognitive impairment, Disability-Off and Disability-LID indices, NMSQuest score, and depressed mood (P < 0.05) (Additional file 1: Table 6). The aforementioned factors also affected PDQ-8. Increases in PD severity or NMQuest score or depressed mood were associated with comparable increase in PDQoL7 or PDQ-8 scores (a change by 1 in these factors would increase PDQoL7 score by 4.22, 4.83 and 4.33 respectively).

The statistically significant factors that had an impact on the PDQoL7 or PDQ-8 scores are shown in Table 3. The proposed models accounted for 61.2% of the variance in the PDQoL7 score with a good fit for the data (ANOVA F-test: 32.08, < 0.001) and 53.6% of the variance in the PDQ-8 score with a good fit for the data (ANOVA F-test: 23.75, P < 0.001).

Table 3 Stepwise multiple regression analysis for PDQoL7 and PDQ-8 scores
Full size table

Discussion

This study describes the development of the PDQoL7 questionnaire for the assessment of the impact of PD on the HRQoL. This short easy to complete tool was developed mainly to cover limitations in the content of the existing PDQ-8. The validity, reliability and the overall properties of PDQoL7 were determined in accordance with scientific best practices and corresponding quality criteria by combining the gaps in existing widely used HRQoL tools for PD patients with findings from the literature review, expert clinician advice, and patient interviews [38, 54, 55]. Consequently, PDQoL7 was compared with the validated Greek versions of PDQ-8 and EQ-5D-5L for criterion validity purposes.

The current study demonstrated that PDQoL7 is an acceptable construct for the determination of HRQoL in PD patients with content validity, convergent validity, internal consistency reliability and non-redundant items that reflect the effect of PD on various aspects of patients’ life.

At first, participants’ demographic and clinical characteristics were in agreement with epidemiological data on PD, revealing that the sample was representative of the PD population [16, 40, 56,57,58,59]. Moreover, although there was a strong correlation both between the PDQoL7 and PDQ-8 summary indices and within each of these tools with the same demographic and clinical parameters, greater variance was accounted for by PDQoL7 compared to PDQ-8. The parameters that contributed to variance in PDQoL7, namely wearing-off, LID and non-motor symptoms are strong predictors of PD progression that contribute to variance in HRQoL assessments in other studies as well [8, 60,61,62,63,64,65,66,67,68,69]. Τhere was no evidence of floor or ceiling effects for PDQoL7. The item to total correlations (range of 0.29–0.63) of PDQoL7 were also satisfactory. The degree to which repeated measurements in the same patients resulted in similar answers is usually investigated in HRQoL tools at 1–2 week intervals and was not investigated in the current study due to the 1-week recall period of PDQoL7 [54].

In addition, based on Cronbach’s a value, PDQoL7 had potentially greater internal consistency and reliability than PDQ-8. The expected strong negative correlation between the EQ-5D-5L index and PDQ-8 scores that has been reported in literature (rs: -0.60 up to -0.78) was observed between EQ-5D-5L and PDQoL7 scores as well [44]. The negative correlation is expected, as PDQoL7/PDQ-8 and EQ-5D-5L scores run in opposite directions. Nevertheless, the stronger negative correlation between EQ-5D-5L and PDQoL7 index scores compared to EQ-5D-5L and PDQ-8 indicates that PDQoL7 is potentially more comprehensive than PDQ-8.

The validity of grouping the items of PDQ-39 and its 8-item short form (PDQ-8) in 8 domains and the initially proposed unidimensionality of PDQ-39 have been questioned [70, 71]. The available evidence suggests, though not confirming, that PDQ-39 may be multidimensional with 3 HRQoL domains, namely physical-functioning, cognition, and socioemotional [11, 14,15,16, 70, 72]. PDQoL7 was also found to be multidimensional with 3 domains. Based on the PDQoL7 items that cluster on the same components, we may suggest that component 1 (“Mobility” and “Skills & Personal-care”) represents physical functioning, component 2 (“Social life/Communication” and “Emotional status) represents socioemotional status and component 3 (“Cognition/Sleep”) represents cognition, bearing in mind the correlation between sleep dysregulation and cognitive decline [32, 37, 63, 73]. The clustering of sleep domain or sleep disturbances under the cognition domain has been demonstrated in other studies, too [30, 63]. In the study by Kim et al. (2014) that investigated inter-relationships between non-motor symptoms (assessed via the Non-Motor Symptoms Scale), two types of non-motor symptom clusters were identified, with sleep/fatigue clustering together with mood, attention/memory, urinary and miscellaneous symptoms (cluster 1), whereas the other cluster included perceptual problems, gastrointestinal issues, and cardiovascular symptoms (cluster 2). Although the three-dimensional structure of PDQoL7 warrants confirmation on a larger sample of patients, nevertheless, it mirrors the suggested three-dimensional structure of PDQ-39, which is more comprehensive than PDQ-8, but also an extensive and time consuming tool [7, 9, 70, 74]. Moreover, compared to the two-dimensional structure of PDQ-8, the proposed three-dimensional structure of PDQoL7 complies with the International Classification of Functioning, Disability and Health by WHO that identifies the components of health that are impacted by diseases or other health conditions and is important for healthcare decision-making purposes [7, 75]. Additionally, the three-dimensional structure of PDQoL7 accounted for greater variance that the corresponding two-dimensional structure of PDQ-8. Although reliability, which can be defined as the homogeneity in a measurement, is distinct from validity, which is associated with the accuracy of a measurement, reliability is a prerequisite for validity [76, 77]. Due to the multidimensional structure of PDQoL7, omega coefficient was also determined, because it is considered more reliable than Cronbach α coefficient for non-unidimensional tools [76, 78,79,80,81]. Omega hierarchical analysis confirmed that PDQoL7 was at least comparable to and slightly more reliable than PDQ-8. Though there is no universally accepted guideline for acceptable or adequate levels of omega reliability for clinical decision making, omega total coefficients should meet the same standards as α coefficients, with high omega total values indicating highly reliable multidimensional constructs [81]. Similarly, omega hierarchical coefficients should exceed 0.50 at a minimum [81]. Due to the lack of published evidence on the dimensionality of PDQ-8, omega coefficients have not been calculated for PDQ-8. Overall, the high omega total value as well as the omega hierarchical > 0.5 for PDQoL7 add further evidence to PDQoL7 as a reliable three-dimensional structure tool.

The study has some limitations that have to be acknowledged to logically evaluate the results. The small sample size is a limitation that may also interfere with the reliability of structure detection. Nevertheless, the purpose of this study was to provide preliminary evidence on the comparative value of PDQoL7 versus PDQ-8. The cross-sectional design is another limitation as PD is a chronic disease and test–retest reliability was not determined. The responsiveness of PDQoL7 in longitudinal studies, the determination of meaningful change threshold and its evaluation on larger cohorts of PD patients across wider geographical regions will be investigated in subsequent studies. However, the consecutive patient enrollment of unselected patients that allowed for the inclusion of PD patients with various clinical and demographic characteristics recruited from a community-based sample reduces the potential for selection bias and may contribute to the low concordance in patients’ assessments and is one of the strengths of the current study. HRQoL assessments are subjective and reflect the demographic and clinical characteristics of the patients under study as well as their health state at the time of the assessments. The assessments and questionnaires were administered to all subjects concurrently under the same conditions and were, therefore, normalized for the patients’ health state and perception of health state at the time. Besides, PD is a heterogeneous disease both in terms of symptoms and progression, thus, the heterogeneity in the patients’ clinical characteristics is anticipated [82].

Nevertheless, a strength of our study is that the questionnaires PDQ-8 and EQ-5D-5L have been validated both in PD patients and in Greek language. Furthermore, the current study confirmed existing published data on PDQ-8 [12, 16, 18, 20, 21, 72, 83,84,85], thus adding to the credibility of the results for PDQoL7. Additionally, the conduct of the study by trained neurologists specialized in movement disorders encompasses an ascertainment of a high level of accuracy in the recognition and evaluation of the different clinical symptoms and signs of the disease. The current results confirmed existing published evidence on PDQ-8, thus, adding further evidence on the validity of the results on PDQoL7. In addition to addressing the gaps of PDQ-8 in non-motor symptom burden, an advantage of PDQoL7 compared to PDQ-8 is its short recall period of 1 week. Recall bias (or memory bias) is the extent to which memory impairment can affect the assessment of a target construct, namely HRQoL, as PD patients suffer from mild cognitive impairment even before PD is diagnosed [86, 87]. Since the ability to accurately remember and report HRQoL affects the reliability and validity of the corresponding instruments and the conclusions that can be drawn, the 1-month recall period of PDQ-8 (or PDQ-39) compared to the 1-week recall period of PDQoL7 increases the potential for patient recall bias. Although the optimal recall period for HRQoL assessments has not been determined and should reflect a balance between minimizing recall bias and maximizing the generalizability of the conclusions [88, 89], PDQoL7 may be better suited for HRQoL assessments in PD patients [10, 86, 90].

Conclusion

This study demonstrates that PDQoL7 is an adequate and easy to use construct-valid tool for the determination of HRQoL in PD patients. PDQoL7 has higher convergent validity and internal consistency (based on Cronbach’s α and omega coefficient) and is more comprehensive compared to PDQ-8 based on its higher correlation with EQ-5D-5L index score. Another advantage of PDQoL7 is the coverage of a broader range of symptoms that impact on quality of life, at any stage of PD, than PDQ-8. Furthermore, the 3-dimensional structure of PDQoL7 is in line with the International Classification of Functioning, Disability and Health and resembles that of the more extensive and time-consuming PDQ-39. PDQoL7 has no floor/ceiling effects. Although the same factors contribute to variance in PDQ-8 and PDQoL7, nevertheless, greater variance is accounted for by PDQoL7. Additionally, PDQoL7 assessments are less prone to bias in assessments by memory deficits due its short recall period [86, 90]. These data warrant investigation in a larger sample of patients and suggest that PDQoL7 could be used to substitute PDQ-8 in HRQoL assessments in PD patients. PDQoL7 may be preferred in settings where a short, comprehensive and reliable HRQoL construct is required that can be regularly used for the objective assessment of motor and non-motor symptom burden across PD patients with various clinical characteristics.

Availability of data materials

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Abbreviations

AR:

Akinetic-rigid

EQ-5D-5L:

5-Level EQ-5D

HR:

Health-related

HRQoL:

Health-related quality of life

MDS-UPDRS:

Movement Disorder Society Unified Parkinson's Disease Rating Scale

LID:

Levodopa-induced dyskinesia

NMSQuest:

Non-motor symptoms questionnaire

NMSS:

Non-motor symptoms scale

PD:

Parkinson’s disease

PDQ-8:

Parkinson's disease questionnaire-8 item version

PDQ-8GrV :

Parkinson's disease questionnaire-8 item Greek validated version

PDQ-39:

Parkinson’s disease questionnaire-39 item version

PDQL:

Parkinson’s disease quality of life questionnaire

PIMS:

Parkinson’s impact scale

PLQ:

Parkinson LebensQualität questionnaire

QoL:

Quality of life

rs :

Spearman’s correlation

TD:

Tremor-dominant

References

  1. Karimi M, Brazier J (2016) Health, health-related quality of life, and quality of life: what is the difference? Pharmacoeconomics 34(7):645–649

    PubMed  Google Scholar 

  2. Healthy People (2020) R. Healthy People 2020 Framework. The Vision, Mission, and Goals of Healthy People 2020. Overarching Goals. [Web] 2020 23 Jun 2021 [cited 2021 22 Jul]

  3. Martinez-Martin P, Jeukens-Visser M, Lyons KE et al (2011) Health-related quality-of-life scales in Parkinson’s disease: critique and recommendations. Mov Disord 26(13):2371–2380

    PubMed  Google Scholar 

  4. Welsh MD (2001) Measurement of quality of life in neurodegenerative disorders. Curr Neurol Neurosci Rep 1(4):346–349

    CAS  PubMed  Google Scholar 

  5. Doward LC, Meads DM, Thorsen H (2004) Requirements for quality of life instruments in clinical research. Value Health 7(Suppl 1):S13–S16

    PubMed  Google Scholar 

  6. Zhao N, Yang Y, Zhang L et al (2021) Quality of life in Parkinson’s disease: a systematic review and meta-analysis of comparative studies. CNS Neurosci Ther 27(3):270–279

    PubMed  Google Scholar 

  7. van Uem JMT, Marinus J, Canning C et al (2016) Health-related quality of life in patients with parkinson’s disease—a systematic review based on the ICF model. Neurosci Biobehav Rev 61:26–34

    PubMed  Google Scholar 

  8. Soh S-E, Morris ME, McGinley JL (2011) Determinants of health-related quality of life in Parkinson’s disease: a systematic review. Parkinsonism Relat Disord 17(1):1–9

    PubMed  Google Scholar 

  9. Martinez-Martin P (2017) What is quality of life and how do we measure it? Relevance to Parkinson’s disease and movement disorders. Mov Disord 32(3):382–392

    PubMed  Google Scholar 

  10. Marinus J, Ramaker C, van Hilten JJ et al (2002) Health related quality of life in Parkinson’s disease: a systematic review of disease specific instruments. J Neurol Neurosurg Psychiatry 72(2):241

    CAS  PubMed  PubMed Central  Google Scholar 

  11. Martínez-Martín P, Rodríguez-Blázquez C, Forjaz MJ et al (2014) Relationship between the MDS-UPDRS domains and the health-related quality of life of Parkinson’s disease patients. Eur J Neurol 21(3):519–524

    PubMed  Google Scholar 

  12. Martinez-Martin P, Rodriguez-Blazquez C, Forjaz MJ et al (2014) Quality of life scales. In: Martinez-Martin P et al (eds) Guide to assessment scales in Parkinson’s disease. Springer, Tarporley, pp 91–102

    Google Scholar 

  13. Opara JA, Brola W, Leonardi M et al (2012) Quality of life in Parkinson’s disease. J Med Life 5(4):375–381

    CAS  PubMed  PubMed Central  Google Scholar 

  14. Hagell P, Nilsson M (2009) The 39-item Parkinson’s Disease Questionnaire (PDQ-39): is it a unidimensional construct? Ther Adv Neurol Disord 2:205–214

    PubMed  PubMed Central  Google Scholar 

  15. Hagell P, Nygren C (2007) The 39 item Parkinson’s Disease Questionnaire (PDQ-39) revisited: implications for evidence based medicine. J Neurol Neurosurg Psychiatry 78(11):1191–1198

    PubMed  PubMed Central  Google Scholar 

  16. Jenkinson C, Fitzpatrick R (2007) Cross-cultural evaluation of the short form 8-item Parkinson’s Disease Questionnaire (PDQ-8): results from America, Canada, Japan, Italy and Spain. Parkinsonism Relat Disord 13(1):22–28

    PubMed  Google Scholar 

  17. Jenkinson C, Fitzpatrick R, Peto V et al (1997) The PDQ-8: Development and validation of a short-form Parkinson’s Disease Questionnaire. Psychol Health 12(6):805–814

    Google Scholar 

  18. Franchignoni F, Giordano A, Ferriero G (2008) Rasch analysis of the short form 8-item Parkinson’s Disease Questionnaire (PDQ-8). Qual Life Res 17(4):541–548

    PubMed  Google Scholar 

  19. Martinez-Martin P, Benito-Leon J, Alonso F et al (2004) Health-related quality of life evaluation by proxy in Parkinson’s disease: approach using PDQ-8 and EuroQoL-5D. Mov Disord 19(3):312–318

    PubMed  Google Scholar 

  20. Huang TT, Hsu HY, Wang BH et al (2011) Quality of life in Parkinson’s disease patients: validation of the short-form eight-item Parkinson’s Disease Questionnaire (PDQ-8) in Taiwan. Qual Life Res 20(4):499–505

    PubMed  Google Scholar 

  21. Katsarou Z, Bostantjopoulou S, Peto V et al (2004) Assessing quality of life in Parkinson’s disease: can a short-form questionnaire be useful? Mov Disord 19(3):308–312

    PubMed  Google Scholar 

  22. Zis P, Martinez-Martin P, Sauerbier A et al (2015) Non-motor symptoms burden in treated and untreated early Parkinson’s disease patients: argument for non-motor subtypes. Eur J Neurol 22(8):1145–1150

    CAS  PubMed  Google Scholar 

  23. Santos-García D, de la Fuente-Fernández R (2013) Impact of non-motor symptoms on health-related and perceived quality of life in Parkinson’s disease. J Neurol Sci 332(1–2):136–140

    PubMed  Google Scholar 

  24. Prakash KM, Nadkarni NV, Lye WK et al (2016) The impact of non-motor symptoms on the quality of life of Parkinson’s disease patients: a longitudinal study. Eur J Neurol 23(5):854–860

    CAS  PubMed  Google Scholar 

  25. Martinez-Martin P, Rodriguez-Blazquez C, Kurtis MM et al (2011) The impact of non-motor symptoms on health-related quality of life of patients with Parkinson’s disease. Mov Disord Off J Mov Disord Soc 26(3):399–406

    Google Scholar 

  26. Huang X, Ng SY, Chia NS et al (2019) Non-motor symptoms in early Parkinson’s disease with different motor subtypes and their associations with quality of life. Eur J Neurol 26(3):400–406

    CAS  PubMed  Google Scholar 

  27. Duncan GW, Khoo TK, Yarnall AJ et al (2014) Health-related quality of life in early Parkinson’s disease: the impact of nonmotor symptoms. Mov Disord Off J Mov Disor Soc 29(2):195–202

    Google Scholar 

  28. Chen H, Zhao EJ, Zhang W et al (2015) Meta-analyses on prevalence of selected Parkinson’s nonmotor symptoms before and after diagnosis. Transl Neurodegen 4(1):1

    Google Scholar 

  29. Rahman S, Griffin HJ, Quinn NP et al (2008) Quality of life in Parkinson’s disease: the relative importance of the symptoms. Mov Disord 23(10):1428–1434

    PubMed  Google Scholar 

  30. Kim EJ, Baek JH, Shin DJ et al (2014) Correlation of sleep disturbance and cognitive impairment in patients with Parkinson’s disease. J Mov Disord 7(1):13–18

    PubMed  PubMed Central  Google Scholar 

  31. Stavitsky K, Neargarder S, Bogdanova Y et al (2011) The impact of sleep quality on cognitive functioning in Parkinson’s disease. J Int Neuropsychol Soc 18:108–117

    PubMed  PubMed Central  Google Scholar 

  32. Pushpanathan ME, Loftus AM, Thomas MG et al (2016) The relationship between sleep and cognition in Parkinson’s disease: a meta-analysis. Sleep Med Rev 26:21–32

    PubMed  Google Scholar 

  33. Chahine LM, Amara AW, Videnovic A (2017) A systematic review of the literature on disorders of sleep and wakefulness in Parkinson’s disease from 2005 to 2015. Sleep Med Rev 35:33–50

    PubMed  Google Scholar 

  34. Havlikova E, van Dijk JP, Nagyova I et al (2011) The impact of sleep and mood disorders on quality of life in Parkinson’s disease patients. J Neurol 258(12):2222–2229

    PubMed  Google Scholar 

  35. Palmeri R, Lo Buono V, Bonanno L et al (2019) Potential predictors of quality of life in Parkinson’s disease: sleep and mood disorders. J Clin Neurosci 70:113–117

    PubMed  Google Scholar 

  36. Pandey S, Bajaj BK, Wadhwa A et al (2016) Impact of sleep quality on the quality of life of patients with Parkinson’s disease: a questionnaire based study. Clin Neurol Neurosurg 148:29–34

    PubMed  Google Scholar 

  37. Zoccolella S, Savarese M, Lamberti P et al (2011) Sleep disorders and the natural history of Parkinson’s disease: the contribution of epidemiological studies. Sleep Med Rev 15(1):41–50

    PubMed  Google Scholar 

  38. Boateng GO, Neilands TB, Frongillo EA et al (2018) Best practices for developing and validating scales for health, social, and behavioral research: a primer. Front Public Health 6:149

    PubMed  PubMed Central  Google Scholar 

  39. Yfantopoulos JN, Chantzaras AE (2017) Validation and comparison of the psychometric properties of the EQ-5D-3L and EQ-5D-5L instruments in Greece. Eur J Health Econ 18(4):519–531

    PubMed  Google Scholar 

  40. Bostantjopoulou S, Katsarou Z, Karakasis C et al (2013) Evaluation of non-motor symptoms in Parkinson’s disease: an underestimated necessity. Hippokratia 17(3):214–219

    CAS  PubMed  PubMed Central  Google Scholar 

  41. MDST F (2003) The Unified Parkinson's disease rating scale (UPDRS): status and recommendations. Mov Disord 18(7):738–750

  42. Hoehn MM, Yahr MD (1967) Parkinsonism: onset, progression and mortality. Neurology 17(5):427–442

    CAS  Google Scholar 

  43. Jankovic J, McDermott M, Carter J et al (1990) Variable expression of Parkinson’s disease. Neurology 40(10):1529

    CAS  PubMed  Google Scholar 

  44. Alvarado-Bolaños A, Cervantes-Arriaga A, Rodríguez-Violante M et al (2015) Convergent validation of EQ-5D-5L in patients with Parkinson’s disease. J Neurol Sci 358:53–57

    PubMed  Google Scholar 

  45. van Hout B, Janssen MF, Feng Y-S et al (2012) Interim scoring for the EQ-5D-5L: mapping the EQ-5D-5L to EQ-5D-3L value sets. Value Health 15(5):708–715

    PubMed  Google Scholar 

  46. Fayers PM, Hand DJ (1997) Factor analysis, causal indicators and quality of life. Qual Life Res 6(2):139–150

    CAS  PubMed  Google Scholar 

  47. Watson M, Law M, Maguire GP et al (1992) Further development of a quality of life measure for cancer patients: the rotterdam symptom checklist (revised). Psychooncology 1(1):35–44

    Google Scholar 

  48. Paci E (1992) Assessment of validity and clinical application of an Italian version of the Rotterdam symptom checklist. Qual Life Res 1(2):129–134

    CAS  PubMed  Google Scholar 

  49. Kaiser HF (1960) The application of electronic computers to factor analysis. Educ Psychol Meas 20(1):141–151

    Google Scholar 

  50. Cattell RB (1966) The scree test for the number of factors. Multivar Behav Res 1(2):245–276

    CAS  Google Scholar 

  51. Horn JL (1965) A rationale and test for the number of factors in factor analysis. Psychometrika 30(2):179–185

    CAS  PubMed  Google Scholar 

  52. Comrey AL, Lee HB (1992) Interpretation and application of factor analytic results. In: A first course in factor analysis. Psychology Press

  53. de Winter JCF, Dodou D, Wieringa PA (2009) Exploratory factor analysis with small sample sizes. Multivar Behav Res 44(2):147–181

    Google Scholar 

  54. Terwee CB, Bot SDM, de Boer MR et al (2007) Quality criteria were proposed for measurement properties of health status questionnaires. J Clin Epidemiol 60(1):34–42

    PubMed  PubMed Central  Google Scholar 

  55. Patrick DL, Burke LB, Gwaltney CJ et al (2011) Content validity–establishing and reporting the evidence in newly developed patient-reported outcomes (PRO) instruments for medical product evaluation: ISPOR PRO good research practices task force report: part 1—eliciting concepts for a new PRO instrument. Value Health 14(8):967–977

    PubMed  Google Scholar 

  56. Konitsiotis S, Bostantjopoulou S, Chondrogiorgi M et al (2014) Clinical characteristics of Parkinson’s disease patients in Greece: a multicenter, nation-wide, cross-sectional study. J Neurol Sci 343:36–40

    PubMed  Google Scholar 

  57. Angelopoulou E, Bozi M, Simitsi A-M et al (2019) The relationship between environmental factors and different Parkinson’s disease subtypes in Greece: data analysis of the Hellenic Biobank of Parkinson’s disease. Parkinsonism Relat Disord 67:105–112

    PubMed  Google Scholar 

  58. Tysnes OB, Storstein A (2017) Epidemiology of Parkinson’s disease. J Neural Transm (Vienna) 124(8):901–905

    Google Scholar 

  59. Qian E, Huang Y (2019) Subtyping of Parkinson’s disease—where are we up to? Aging Dis 10(5):1130–1139

    PubMed  PubMed Central  Google Scholar 

  60. Zhang H, Gu Z, An J et al (2014) Non-motor symptoms in treated and untreated Chinese patients with early Parkinson’s disease. Tohoku J Exp Med 232(2):129–136

    PubMed  Google Scholar 

  61. Winter Y, von Campenhausen S, Arend M et al (2011) Health-related quality of life and its determinants in Parkinson’s disease: results of an Italian cohort study. Parkinsonism Relat Disord 17(4):265–269

    PubMed  Google Scholar 

  62. Schrag A, Jahanshahi M, Quinn N (2000) What contributes to quality of life in patients with Parkinson’s disease? J Neurol Neurosurg Psychiatry 69:308–312

    CAS  PubMed  Google Scholar 

  63. Rodríguez-Violante M, Cervantes-Arriaga A, Corona T et al (2013) Clinical determinants of health-related quality of life in Mexican patients with Parkinson’s disease. Arch Med Res 44(2):110–114

    PubMed  Google Scholar 

  64. Li H, Zhang M, Chen L et al (2010) Nonmotor symptoms are independently associated with impaired health-related quality of life in Chinese patients with Parkinson’s disease. Mov Disord Off J Mov Disord Soc 25(16):2740–2746

    Google Scholar 

  65. Karlsen KH, Larsen JP, Tandberg E et al (1999) Influence of clinical and demographic variables on quality of life in patients with Parkinson’s disease. J Neurol Neurosurg Psychiatry 66(4):431–435

    CAS  PubMed  Google Scholar 

  66. Gómez-Esteban JC, Zarranz JJ, Lezcano E et al (2007) Influence of motor symptoms upon the quality of life of patients with Parkinson’s disease. Eur Neurol 57(3):161–165

    PubMed  Google Scholar 

  67. Dams J, Klotsche J, Bornschein B et al (2013) Mapping the EQ-5D index by UPDRS and PDQ-8 in patients with Parkinson’s disease. Health Qual Life Outcomes 11:35–35

    PubMed  Google Scholar 

  68. Chapuis S, Ouchchane L, Metz O et al (2005) Impact of the motor complications of Parkinson’s disease on the quality of life. Mov Disord Off J Move Disord Soc 20(2):224–230

    Google Scholar 

  69. Carod-Artal FJ, Vargas AP, Martinez-Martin P (2007) Determinants of quality of life in Brazilian patients with Parkinson’s disease. Mov Disord Off J Mov Disord Soc 22(10):1408–1415

    Google Scholar 

  70. Ophey A, Eggers C, Dano R et al (2018) Health-related quality of life subdomains in patients with Parkinson’s disease: the role of gender. Parkinson’s Dis 2018:6532320–6532320

    Google Scholar 

  71. Nilsson MH, Westergren A, Carlsson G et al (2010) Uncovering indicators of the international classification of functioning, disability, and health from the 39-item Parkinson’s Disease Questionnaire. Parkinson’s Dis 20:984673

    Google Scholar 

  72. Chen K, Yang Y-J, Liu F-T et al (2017) Evaluation of PDQ-8 and its relationship with PDQ-39 in China: a three-year longitudinal study. Health Qual Life Outcomes 15(1):170

    PubMed  PubMed Central  Google Scholar 

  73. Huang J, Zhuo W, Zhang Y et al (2017) Cognitive function characteristics of parkinson’s disease with sleep disorders. Parkinson’s Dis 2017:4267353–4267353

    Google Scholar 

  74. Wood-Dauphinee S (1999) Assessing quality of life in clinical research: from where have we come and where are we going? J Clin Epidemiol 52(4):355–363

    CAS  PubMed  Google Scholar 

  75. WHO (2001) International classification of functioning, disability and health. Cited 2021 05 Oct

  76. Najera H (2019) Reliability, population classification and weighting in multidimensional poverty measurement: a Monte Carlo study. Soc Indic Res 142:887–910

    Google Scholar 

  77. Streiner DL, Norman GR, Cairney J (2015) Health measurement scales: a practical guide to their development and use, 5th ed. Health measurement scales: a practical guide to their development and use. Oxford University Press, New York, pp 399-xiii

  78. Revelle W, Zinbarg RE (2008) Coefficients Alpha, Beta, Omega, and the glb: comments on Sijtsma. Psychometrika 74(1):145

    Google Scholar 

  79. Zinbarg RE, Revelle W, Yovel I et al (2005) Cronbach’s α, Revelle’s β, and Mcdonald’s ωH: their relations with each other and two alternative conceptualizations of reliability. Psychometrika 70:123–133

    Google Scholar 

  80. McDonald R (1999) Test theory: a unified treatment, 1st edn. Psychology Press

    Google Scholar 

  81. Watkins MW (2017) The reliability of multidimensional neuropsychological measures: from alpha to omega. Clin Neuropsychol 31(6–7):1113–1126

    PubMed  Google Scholar 

  82. Greenland JC, Williams-Gray CH, Barker RA (2019) The clinical heterogeneity of Parkinson’s disease and its therapeutic implications. Eur J Neurosci 49(3):328–338

    PubMed  Google Scholar 

  83. Tan LCS, Lau P-N, Au W-L et al (2007) Validation of PDQ-8 as an independent instrument in English and Chinese. J Neurol Sci 255(1–2):77–80

    PubMed  Google Scholar 

  84. Kahraman T, Genç A, Söke F et al (2018) Validity and reliability of the Turkish version of the 8-item Parkinson’s Disease Questionnaire. Noro Psikiyatri Arsivi 55(4):337–340

    PubMed  PubMed Central  Google Scholar 

  85. Fereshtehnejad S-M, Naderi N, Rahmani A et al (2014) Psychometric study of the Persian short-form eight-item Parkinson’s disease questionnaire (PDQ-8) to evaluate health related quality of life (HRQoL). Health Qual Life Outcomes 12:78

    PubMed  PubMed Central  Google Scholar 

  86. Fengler S, Liepelt-Scarfone I, Brockmann K et al (2017) Cognitive changes in prodromal Parkinson’s disease: a review. Mov Disord 32(12):1655–1666

    PubMed  Google Scholar 

  87. Aarsland D (2016) Cognitive impairment in Parkinson’s disease and dementia with Lewy bodies. Parkinsonism Relat Disord 22(Suppl 1):S144–S148

    PubMed  Google Scholar 

  88. Clarke PM, Fiebig DG, Gerdtham UG (2008) Optimal recall length in survey design. J Health Econ 27(5):1275–1284

    PubMed  Google Scholar 

  89. Stull DE, Leidy NK, Parasuraman B et al (2009) Optimal recall periods for patient-reported outcomes: challenges and potential solutions. Curr Med Res Opin 25(4):929–942

    PubMed  Google Scholar 

  90. Weintraub D, Chahine LM, Hawkins KA et al (2017) Cognition and the course of prodromal Parkinson’s disease. Mov Disord 32(11):1640–1645

    CAS  PubMed  PubMed Central  Google Scholar 

Download references

Acknowledgements

Excelya Greece is acknowledged for medical writing support.

Funding

Not applicable.

Author information

Authors and Affiliations

  1. Department of Neurology, Mediterraneo Hospital, 8-12 Ilias Street, 16675, Glyfada, Athens, Greece

    Pantelis Stathis & George Papadopoulos

Authors
  1. Pantelis Stathis
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. George Papadopoulos
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

PS was responsible for the development of PDQoL7 questionnaire, overall study (conception, organization and execution) as well as review and critique of the statistical analysis and preparation of manuscript. GP provided clinical assistance. Both authors read and approved the final manuscript.

Authors’ information

Pantelis Stathis MD, PhD Head of the Department of Neurology of Mediterraneo Hospital, Athens, Scientific Director of Cerebral Palsy, Greece. Past member of the executive committee of the Movement Disorders Branch of the Hellenic Neurological Society. PhD from Lab of Experimental Pharmacology Medical School National and Kapodistrian University of Athens. Resident in Neurology at the Medical School of the National Kapodistrian University of Athens, at the Aeginition Hospital. Medical studies at the Medical School of the Aristotle University of Thessaloniki.

Georgios Papadopoulos MD - Consultant Neurologist. Medical School, Democritus University of Thrace, MD, 2002. Resident in Neurology Eginition Hospital, Athens November 2011 - February 2016. Medical Specialty Lisence in Neurology 2016. Consultant Neurologist Eginition Hospital, Athens March 2016 - April 2017. Consultant Neurologist Mediterraneo Hospital, Since May 2017.

Corresponding author

Correspondence to Pantelis Stathis.

Ethics declarations

Ethics approval and consent to participate

The study received approval from the Mediterraneo’s Hospital scientific committee and all patients provided informed consent.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Additional information

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary Information

Additional file 1

. Supplementary material that includes Figure 1 and Tables 1-6 can be found in the respective file submitted via the Manuscript Tracking System.

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Stathis, P., Papadopoulos, G. Evaluation and validation of a patient-reported quality-of-life questionnaire for Parkinson’s disease. J Patient Rep Outcomes 6, 17 (2022). https://doi.org/10.1186/s41687-022-00427-0

Download citation

  • Received:

  • Accepted:

  • Published:

  • DOI: https://doi.org/10.1186/s41687-022-00427-0

Keywords

  • Quality of life
  • Parkinson’s disease
  • Questionnaire
  • Patient-reported outcomes