Real-PD Trial: Development of Clinical Prognostic Models for Parkinson's Disease: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Real-PD Trial: Development of Clinical Prognostic Models for Parkinson's Disease (NCT02474329), a registered phase not stated study. The primary outcome is Parkinson's Disease Symptoms.

2. Clinical Question

These aims are related but not identical. The baseline MDS-UPDRS characterizes participants’ symptoms; by itself, a baseline measurement does not show how symptoms change over time. Sensor and app measures are intended to describe activity, falls, tremor, medication annotations and mood reports. The registry record does not provide results that establish how completely participants used the devices or how those measures related to symptom burden.

3. Trial Design

Real-PD is recorded as a completed, population-based study of Parkinson’s disease. Its description identifies the study as observational and says Dutch patients were to be recruited across the country. The registry lists enrollment of 304. The brief summary describes an intended enrollment of 1000 patients with Parkinson’s disease and 250 physiotherapists; how that planned enrollment relates to the recorded enrollment is not explained in the registry record.

The study description combines a short version of the Parkinson’s Progression Markers Initiative protocol with remote monitoring. Trained physiotherapists were to perform a standardized clinical assessment, including the MDS-UPDRS. Participants were also described as using a Pebble smartwatch, a fall detector and the Fox Insight Android app during 13 weeks. The stated monitoring interests include physical activity, falls and tremor, as well as self-reported medication intake and mood.

The record describes five geographic cohorts, with locations in different Dutch regions. These are not presented as randomized intervention groups, and no treatment allocation is stated. A comparison between the regions should therefore not be treated as a randomized estimate of a treatment effect. The registry record does not explain whether regional differences were intended for formal statistical comparison.

The primary outcome is a baseline MDS-UPDRS total score, reported in units on a scale with the median and full range specified as the summary format. Although the study summary discusses monitoring over time, the primary endpoint itself is explicitly a one-point baseline assessment. The record does not report further scheduled primary-outcome measurements or a longitudinal primary analysis.

The record gives a start date of 2015-07, a primary completion date of 2016-11 and a completed status. It does not report the recruitment process in enough detail to assess selection, nor does it give a statistical analysis plan or explain the intended handling of regional clustering.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: After changing the inclusion process for one cohort only, a total of 347 eligible PD patients were invited to participate. Among those invited, 43 refused to participate. The main refusal reasons were "Study protocol seems too burdensome" (44%, n = 19), followed by "Personal circumstances" (33%, n = 14). A total of 304 patients (enrolment rate = 88%) were enrolled.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: We have analysed data from all participants who completed the study.

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

Population: Inclusion was changed from 5 cohorts (total of 100 participants) to 1 cohort only.

6. Primary Endpoint

The registry lists the primary outcome as Parkinson's Disease Symptoms, measured over Baseline.

The primary endpoint is the total MDS-UPDRS score at baseline. The MDS-UPDRS revises the Unified Parkinson’s Disease Rating Scale and is intended to characterize several aspects of Parkinson’s disease, including non-motor and motor experiences of daily living and motor complications. The registry says the total is formed by summing scores from its four subscales, covering parts I through IV. The scale ranges from 0 to 272, with higher scores indicating greater disease severity and burden.

The endpoint is useful for describing symptom burden across participants at the assessment point. A median gives the middle of the observed score distribution and is less affected by extreme values than a mean. The full range conveys the observed spread from the lowest to the highest value, although it does not show how densely observations cluster between those extremes. These are general properties of the chosen summaries.

The registry specifies one baseline assessment, rather than a change score or a repeated-measures endpoint. It can therefore characterize the participants assessed, but it cannot alone quantify progression or improvement over time. The actual median and full range are not reported in the registry record, so the posted record does not permit a numerical description of baseline symptom burden.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry specifies a median and full range for the primary MDS-UPDRS score. These summaries describe different features of a distribution. The median is its central value: half of the observations are at or below it and half are at or above it, allowing for ties. The range records the lowest and highest values. As a general statistical point, the range is sensitive to extreme observations and does not describe how scores are distributed between its endpoints. The record does not provide the actual median or range, so these definitions cannot be applied to a numerical result.

What does the MDS-UPDRS total represent?

The registered total is the sum of scores from the four MDS-UPDRS parts. The registry describes the measure as covering non-motor and motor experiences of daily living and motor complications. Its possible total scores range from 0 to 272, with higher scores indicating more severe disease burden. A sum compresses multiple domains into one score, which can make an overall description convenient, but it does not show each domain’s separate contribution. The registry record does not report subscale results.

Why does the baseline timing matter?

The primary endpoint is explicitly measured at baseline in a one-point assessment. A single assessment can characterize participants at that point, but it does not measure within-participant change. General analyses of progression require measurements over time and a defined approach to comparing them. Although the study summary describes device and app monitoring during 13 weeks, the primary outcome is not described as a repeated MDS-UPDRS measure. The registry record does not report a longitudinal analysis of the primary endpoint.

What does an observational design imply?

In an observational study, exposures or monitoring experiences are not assigned through a stated randomized treatment allocation. This limits the interpretation of group comparisons: characteristics that differ between groups may also be associated with an outcome. Random allocation is one general method for balancing such factors across groups, but the registry does not define a randomized comparison. The regional cohorts should therefore be understood as cohort descriptions, not as evidence of treatment groups with exchangeable participants. No adjustment strategy for differences among cohorts is reported.

How should planning calculations be read?

The registry describes sample-size illustrations based on a stated fraction of an observed effect. It specifies a two-sided significance level of 0.05, equal allocation between two arms and a normal approximation. These are planning assumptions, not a description of the observational study’s reported analysis. The registry record does not report the observed effect value used for the illustrations or a trial design based on a two-arm comparison. Any participant counts in such calculations are hypothetical planning quantities; they are not observed power and do not demonstrate that the study had a particular probability of detecting an effect.

In general, a sample-size calculation asks what sample size would be needed under specified assumptions. Its result depends on the effect to detect, the variability or event rate, the significance threshold and the allocation and analysis assumptions. A calculation based on a fraction of an observed effect is especially dependent on that chosen effect. The record’s description of calculation assumptions does not substitute for a prospective sample-size justification, which is not reported in the registry record.

Why does over-dispersion matter for counts?

Several registered measures are counts, including falls and app annotations. In general, a simple count model may assume that variability is linked to the mean in a particular way. Over-dispersion means the observed variability is greater than that model allows; ignoring it can make uncertainty estimates too small and statistical evidence appear stronger than it is. Alternative models or robust uncertainty estimates can address this issue, depending on the data and design. The registry record does not report the count models, distributional checks or variance adjustments used.

The record reports no analyses and does not provide outcome estimates, standard errors, confidence intervals or p-values. Consequently, it is not possible to assess which statistical models were applied, how uncertainty was quantified, or whether model assumptions were checked. General descriptions of statistical methods explain what those methods can do; they do not establish that a particular method was used in Real-PD.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists 11 outcome measures and names several secondary measures, including falls, mood reports, medication annotations, activity and questionnaire scores. When multiple outcomes are tested, the chance of at least one false-positive result can increase. General approaches include defining a primary outcome in advance, adjusting for multiple tests, or treating secondary analyses as exploratory. The registry record does not report a multiplicity strategy, a hierarchy among secondary outcomes, or an analysis plan for multiple comparisons. Since no analyses are posted, there are no reported p-values whose multiplicity adjustment can be assessed.

The primary-outcome population is described as all participants who completed the study. The number of completers and the number with an observed MDS-UPDRS score are not reported in the registry record. The record does not say how missing outcome measurements were handled, whether reasons for missingness were collected, or whether any imputation or sensitivity analysis was used. General statistical practice distinguishes missingness from an observed value; the missing-data mechanism can affect how representative a complete-case analysis is, but that mechanism cannot be evaluated from the record.

The registry does not provide an intention-to-treat population, a per-protocol population or other analysis-population definitions. Because no randomized allocation is stated, an intention-to-treat treatment comparison is not established by the study description. The record’s safety entry reports 291 at risk, but does not explain how that denominator relates to the outcome population or to completeness for individual device and app measures. Those analysis-population details are not reported in the registry record.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The registry safety entry lists 291 participants at risk for the reported group. It records 0 serious adverse events and 0 other adverse events. These are the counts entered in the safety fields; they should be read alongside the recorded denominator and the limits of the registry entry.

The group is labeled Cohort 1, with a note that the study included one cohort. Elsewhere, the study description identifies five geographic cohorts. The registry record does not explain this difference in presentation, so the safety entry’s group label should not be taken as a clear account of how safety data were organized across all geographic groups.

The death field is null, which means deaths are not reported in the registry record; it is not a reported zero. The absence of recorded adverse-event counts does not establish that no events occurred outside the entered safety data, nor does it describe how events were collected or monitored. The record does not provide event definitions, surveillance details or a safety analysis. These figures describe what is entered in the registry and do not support broader conclusions about safety.

12. What the Result Does, and Does Not, Mean

Real-PD’s registry record describes a study designed to combine clinical assessment with wearable and app-based monitoring in people with Parkinson’s disease. It identifies a baseline MDS-UPDRS total score as the primary outcome and names multiple measures related to activity, falls, medication, mood and other health characteristics. These features show the study’s measurement aims, but the record does not report numerical outcome results.

The listed enrollment is 304, and the study status is completed. Completion and enrollment describe study conduct; neither alone gives the number with complete outcome data or demonstrates that the intended monitoring was feasible or well tolerated. The record does not report device adherence, app-use completeness or the proportion of participants contributing particular measurements. Those questions cannot be answered from the study status alone.

The record also does not show whether the sensor measures corresponded to clinical symptom burden, whether mood or medication annotations were associated with activity, or whether any of these measures changed over the monitoring period. Such conclusions require reported analyses, including estimates and information about uncertainty. No analyses are posted in the registry record.

The observational design is important to interpretation. The study does not define a randomized treatment comparison, so it cannot provide a randomized estimate of the effect of a treatment. Regional cohorts do not by themselves serve as controls. Even if group values were available, differences could reflect differences in participant characteristics or other factors, and the record does not describe an adjustment plan.

The result record therefore supports a description of the intended measures, design and reported enrollment, but not a conclusion about clinical effectiveness, progression, feasibility rates or the strength of associations. This distinction is not a judgment about the study’s value; it reflects the difference between registering a measurement plan and reporting analyzed outcome data.

13. Why This Trial Matters Statistically

Real-PD raises a statistical question that is increasingly relevant to clinical research: how to turn continuous streams from wearable devices and self-report apps into interpretable measures. Activity, falls, tremor, medication annotations and mood reports differ in how they are recorded and in how often observations may be available. A useful analysis needs clear definitions of each measure, a specified observation period and a transparent approach to incomplete or irregular data. The registry describes several intended measures but does not report these analytic details.

The study also pairs remote monitoring with a standardized clinical assessment. That combination can be valuable for research because sensor-derived measures and clinician-rated scales capture different kinds of information. A baseline MDS-UPDRS total can characterize symptom burden, while device data may describe behaviors during daily life. Whether the measures agree, complement each other or reflect distinct domains must be examined empirically; the registry record does not report such findings.

Statistically, feasibility and outcome association are separate questions. Feasibility concerns whether participants can and do use the devices and app as intended. Association concerns how measurements relate to clinical characteristics or outcomes. A completed study alone does not answer either question. Reporting participant-level completeness, distributions, uncertainty and the handling of repeated observations would be important for interpreting those aims.

The registry’s lack of posted analyses also illustrates why outcome definitions and results need to be read separately. A specified endpoint tells readers what was intended to be measured; it does not reveal the observed value or how precise an estimate is. Here, the primary measure is described clearly, but its median and range are not reported.

14. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The registry record leaves several trial-specific limitations unresolved. The study summary describes planned participation by 1000 patients and 250 physiotherapists, while the enrollment field records 304. The record does not explain whether this reflects a change in recruitment plans, differences in what was counted, or another reason. It is therefore not possible to assess the enrollment against the original target from the record alone.

The primary outcome is a baseline assessment, although the broader study aims include learning about disease patterns and monitoring behavior. A single baseline score cannot describe change in symptom burden. The brief study description refers to monitoring during 13 weeks, but the registry does not report how much sensor or app data were available for each participant or whether the monitoring period was completed as intended.

The record describes geographic cohorts but does not state how regional differences were to be analyzed or whether recruitment and measurement procedures were comparable across locations. It also does not report participant characteristics, actual primary-outcome summaries, secondary-outcome estimates, a statistical analysis plan or methods for missing data. These omissions prevent assessment of selection, representativeness, precision and robustness.

Finally, the safety entry’s single-cohort label is not reconciled with the five geographic cohorts described elsewhere, and the death field is not reported. These registry entries limit interpretation of the safety denominator and do not permit an assessment of event ascertainment.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Real-PD Trial: Development of Clinical Prognostic Models for Parkinson's Disease — NCT02474329.
• Registry record last updated 2021-12-06; status last verified 2017-10.
• Results first posted 2021-12-06.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

18. Record Summary

NCT02474329 is the registry record for the Real-PD Trial: Development of Clinical Prognostic Models for Parkinson’s Disease, sponsored by Radboud University Medical Center. The study is marked completed, with a start date of 2015-07, a primary completion date of 2016-11 and enrollment of 304. It is described as an observational, population-based study involving clinical assessment and wearable and app-based monitoring.

The primary outcome is the baseline MDS-UPDRS total score, summarized by median and full range. The registry record describes the scale and its interpretation but does not report the observed primary outcome value. It lists secondary measures related to falls, mood, medication annotations, activity and other assessments, but no analysis results are posted. The record describes intended enrollment of 1000 patients and 250 physiotherapists in its summary, without explaining how those targets relate to the recorded enrollment.