Parkinson’s Disease Quality of Life Questionnaire

Abstract

The Parkinson’s Disease Quality of Life questionnaire (PDQL) is a specialized Quality of Life (QoL) assessment tool designed specifically for patients diagnosed with Parkinson’s disease. This self-report or interviewer-assisted instrument measures the impact of the disease on daily functioning and well-being over the preceding three months. The PDQL consists of 37 items structured across four essential subscales, providing a comprehensive profile of the patient’s lived experience. Higher scores on the PDQL are indicative of a better perceived quality of life.

Keywords

Parkinson’s disease, Quality of life, PDQL, QoL assessment, neurological disorder, self-report, psychometrics, subscales, emotional functioning, social functioning.

Authors

de Boer AGEM, et al. (1996)

Purpose

The primary purpose of the PDQL is to provide a reliable and clinically relevant measure of health-related Quality of Life (HRQoL) specifically tailored to the unique challenges faced by individuals suffering from Parkinson’s disease (PD). It is intended for use in clinical trials, outcome measurement studies, and routine clinical practice to monitor disease progression and the efficacy of therapeutic interventions.

The instrument’s focus on the preceding three months allows clinicians and researchers to establish a stable baseline of functioning, mitigating the influence of transient symptoms. By incorporating patient perspectives, the PDQL ensures that assessments of care and treatment outcomes reflect genuine improvements in the patient’s overall well-being, encompassing physical, emotional, and social domains.

Construct

The PDQL measures the multidimensional construct of health-related Quality of Life as experienced by patients with Parkinson’s disease. This construct is operationalized through four distinct subscales, which capture the diverse manifestations of the disease beyond purely motor symptoms. The 37 items collectively assess the extent to which PD impacts physical comfort, emotional state, and social integration.

The four identified domains are: Parkinson symptoms (motor function and physical discomfort), Systemic symptoms (non-motor physical complaints), Emotional functioning (mood, anxiety, and psychological distress), and Social functioning (social activities, relationships, and perceived stigma). This structure ensures a holistic evaluation of the patient’s personal factors and their interaction with the movement system and socio-social life.

Validity

Initial validation studies conducted by the authors in 1996 established the strong psychometric properties of the PDQL. Evidence for construct validity was demonstrated through correlations with established measures of general health status and specific Parkinsonian disability scales, showing that the PDQL measures the intended construct and differentiates between groups with varying levels of disease severity.

Furthermore, discriminant validity was confirmed by showing low correlations between the PDQL and measures assessing unrelated constructs. The scale exhibits good known-groups validity, successfully distinguishing between patients classified by different stages of the Hoehn and Yahr scale, thereby confirming its utility as a sensitive measure of disease progression impact on QoL.

Reliability

The PDQL demonstrates high levels of internal consistency across its four subscales and for the total scale score. Internal consistency, typically measured using Cronbach’s alpha, generally exceeds 0.80 for the total score, indicating that the items within the scale reliably measure the same underlying construct. This robust internal structure supports the clinical application of the instrument.

Test-retest reliability has also been established, confirming the stability of the measure over short periods in clinically stable patients. High test-retest coefficients suggest that changes in PDQL scores over time are likely attributable to genuine changes in the patient’s quality of life or disease status, rather than measurement error. These properties are crucial for using the PDQL as an outcome measure.

Factor Analysis

The original development of the PDQL utilized factor analysis to confirm the theoretical structure of the instrument. Exploratory and confirmatory factor analysis techniques supported the hypothesized four-factor model, corresponding precisely to the four subscales: Parkinson Symptoms, Systemic Symptoms, Emotional Functioning, and Social Functioning. This statistical validation confirmed that the 37 items appropriately cluster into meaningful domains.

Subsequent cross-cultural validation studies have generally replicated the four-factor structure, although minor variations in item loadings may occur depending on the specific population and language used. The consistent factor structure across diverse samples underscores the PDQL’s robust theoretical foundation and its suitability for international research.

Instrument

Test Type: Questionnaire / Self-report Inventory

Format: 37 items, using a Likert-type response format (usually concerning frequency or severity over the past three months). The scale can be self-administered or interviewer-assisted.

Language Available: Originally developed in Dutch, widely translated and validated in numerous languages (e.g., English, German, Spanish, Chinese).

Population Group: Patients diagnosed with Parkinson’s disease.

Age Group: Adults and the Elderly.

Population Details: Individuals undergoing assessment or treatment for Parkinson’s disease, covering functions related to the movement system, personal factors, and socio-social life.

Test Methodology: The scale measures problems experienced over a retrospective period of three months. A higher total score indicates a higher perceived Quality of Life. The scoring system aggregates scores across the four subscales to yield an overall QoL index.

The original explanatory form (Toelichtingsformulier) for the instrument can be downloaded here: PDQL-form.pdf

Keywords

HRQoL, Parkinson symptoms, systemic symptoms, emotional functioning, social functioning, psychometric assessment, movement disorder, neurological scale, factor analysis, clinical outcomes.

Authors

Author ORCID Identifier: N/A (Information not provided in source material)

Affiliation Email addresses: N/A (Information not provided in source material)

Correspondence Address: N/A (Information not provided in source material)

Permissions & Fee and Test Year

The PDQL was first published and documented in 1996 by de Boer AGEM and colleagues. Information regarding current usage permissions and associated fees should be directed to the original authors or the publishing institution that holds the copyright for the specific language version being utilized.

The scale is recognized globally for its contribution to measuring outcomes in PD research. Researchers and clinicians should verify licensing requirements, as many translations and adaptations may require specific permissions for commercial or large-scale academic use.

Reference’s

• de Boer AGEM, et al. (1996). Development of a disease specific quality of life questionnaire for patients with Parkinson’s disease. Journal of Neurology, Neurosurgery, and Psychiatry, 61, 470–476.
• Additional references detailing cross-cultural validation and responsiveness to change are available in subsequent literature focusing on Parkinson’s disease outcome measures.

Items of the Parkinson’s Disease Quality of Life questionnaire

IMPORTANT: The following scale items must be preserved in their original language and must not be changed in any way.

The PDQL is comprised of 37 items distributed across four subscales:

• Parkinson symptomen
• Systemische symptomen
• Emotioneel functioneren
• Sociaal functioneren