Parkinson’s Disease Questionnaire (PDQ-39)
A 39-item self-reported quality-of-life questionnaire for Parkinson’s disease.
By Claire White
- Self-administered on paper. Takes 10 to 20 minutes. No training needed to give it.
- 39 items across 8 areas of life, from mobility to bodily discomfort.
- Each item is scored 0 to 4. Each area is then standardised to a 0 to 100 score, where lower means better quality of life.
- A single summary index, the PDSI, is the average of the 8 area scores.
- Distributed by Oxford University Innovation.
Psychometrics
Ranges across the eight scales, from Hagell and Nygren (2007), a postal survey of 202 people with Parkinson's. Higher is better.
What does the PDQ-39 measure?
Health-related quality of life, as the person living with Parkinson’s reports it, rather than the severity a clinician observes. It asks how often each of 39 problems has affected you, grouped into eight areas of life. Mobility and daily activities cover the practical side. Emotional well-being, stigma, social support, and cognition cover the parts a motor examination never reaches. Communication and bodily discomfort cover the rest.
| Area | Items |
|---|---|
| Mobility | 10 |
| Activities of daily living | 6 |
| Emotional well-being | 6 |
| Stigma | 4 |
| Cognition | 4 |
| Social support | 3 |
| Communication | 3 |
| Bodily discomfort | 3 |
What does a PDQ-39 score mean?
Each area is standardised to run from 0 to 100, and lower is better. That is the reverse of the MDS-UPDRS and the most common source of misreading, so it is worth saying once plainly. A rising PDQ-39 score is bad news. The summary index averages the eight areas into one number on the same 0 to 100 scale.
The literature publishes no agreed severity bands for the PDQ-39, so there is no table of mild, moderate, and severe here. It is designed to be read as change over time in the same person. What the literature does publish is how much change counts. Across 985 paired assessments in 365 people, 4.72 points of improvement and 4.22 points of worsening on the summary index were the smallest differences that were clinically meaningful.
Two limits are worth stating plainly. The questionnaire has an average floor effect of 15%, so it separates people less well at the mild end. And a formal re-analysis found the item grouping into these eight areas is only partly supported, with scaling success averaging 56.2%, which is a reason to read the summary index rather than lean hard on any one area score. Results are reference information for you and your care team, not a diagnosis.
How the PDQ-39 is administered
- Administered by
- The person, as a self-completed questionnaire
- Time to administer
- 10 to 20 minutes
- Equipment
- A paper copy and a pen
- Cost
- Free to take here.
- Published by
- Oxford University Innovation
- Training required
- None
- Age range
- Adults
Which conditions is the PDQ-39 used for?
Related instruments
- MDS-UPDRSThe clinician's rating of Parkinson's severity, which the PDQ-39 is usually read alongside
- MDS-UPDRS Part IIDaily function rather than quality of life, also reported by the person
- EQ-5DGeneric health-related quality of life, for comparing Parkinson's against other conditions
- EORTC QLQ-C30The same idea built for cancer, if you want to see how disease-specific quality-of-life scales are constructed
PDQ-39 questions, answered
How is the PDQ-39 scored?
In two steps. You rate each of the 39 items from 0 to 4 for how often the problem affected you. For each of the eight areas, the item scores are added, divided by the highest score that area could reach, and multiplied by 100, which puts every area on the same 0 to 100 scale even though they have different numbers of items. The summary index, the PDSI, is those eight area scores added and divided by 8.
What is a good PDQ-39 score?
A low one. 0 means no reported problem in that area and 100 means the maximum, so the direction is the opposite of most rating scales. There are no agreed severity bands for the PDQ-39, so a single score is read against your own earlier scores rather than against a published cutoff. It is also worth knowing the questionnaire has an average floor effect of 15%, meaning it separates people less well when things are going comparatively well.
How much change in the PDQ-39 is meaningful?
About 4 to 5 points on the summary index. In 985 paired assessments across 365 people, 4.72 points of improvement and 4.22 points of worsening were the smallest changes that registered as clinically meaningful. Smaller movements than that are within the noise of the instrument.
How long does the PDQ-39 take?
10 to 20 minutes. You fill it in yourself, on paper, and no training is needed to give it to you. That makes it one of the easier Parkinson's instruments to complete before an appointment rather than during one.
Is the PDQ-39 free?
Yes. It is free to take here. The questionnaire itself is distributed by Oxford University Innovation, which is who to approach about administering it in your own practice.
What is the PDQ-8?
A short form of the same questionnaire, with eight items instead of 39, reported as its own summary index. It trades detail for speed. Its meaningful-change thresholds are wider than the PDQ-39's, at 5.94 points for improvement and 4.91 for worsening, which is the cost of the shorter form.
Evidence, psychometrics and provenance
Developed at Oxford by Peto, Jenkinson, Fitzpatrick and Greenhall, who built the item pool from interviews with people who had Parkinson’s and then refined it against postal survey data. The 39-item questionnaire with its eight scales was published in 1995. Two years later the same group factor-analysed those eight scales, found a single underlying factor in two separate samples, and added the summary index on that basis.
- Meaningful improvement (summary index)
- 4.72 points, from 985 paired assessments (Horvath et al., 2017)
- Meaningful worsening (summary index)
- 4.22 points, from the same cohort (Horvath et al., 2017)
- Item grouping
- Scaling success averaged 56.2%, so the current eight-scale grouping is not fully supported (Hagell and Nygren, 2007)
- Floor effects
- 15% on average, so the questionnaire discriminates less well at the mild end (Hagell and Nygren, 2007)
References
- 1.Peto V, Jenkinson C, Fitzpatrick R, Greenhall R. The development and validation of a short measure of functioning and well being for individuals with Parkinson's disease. Qual Life Res. 1995;4(3):241-248.
- 2.Jenkinson C, Fitzpatrick R, Peto V, Greenhall R, Hyman N. The Parkinson's Disease Questionnaire (PDQ-39): development and validation of a Parkinson's disease summary index score. Age Ageing. 1997;26(5):353-357.
- 3.Hagell P, Nygren C. The 39 item Parkinson's disease questionnaire (PDQ-39) revisited: implications for evidence based medicine. J Neurol Neurosurg Psychiatry. 2007;78(11):1191-1198.
- 4.Horvath K, Aschermann Z, Kovacs M, et al. Changes in quality of life in Parkinson's disease: how large must they be to be relevant? Neuroepidemiology. 2017;48(1-2):1-8.
- 5.Shirley Ryan AbilityLab. Rehabilitation Measures Database: Parkinson's Disease Questionnaire-39. Administration, cost, the eight dimensions and their item counts, and the scoring formulae.
This assessment uses a validated instrument and is reference information, not a diagnosis.