The Effects of Dual Task Training in Individuals With Parkinson's Disease: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Effects of Dual Task Training in Individuals With Parkinson's Disease (NCT02538029), a randomized na study. The primary outcome is Step Length During Gait.

2. Clinical Question

3. Trial Design

The Cleveland Clinic sponsored this completed study, registered as NCT02538029. The record describes a randomized, single-masked, parallel design and lists Parkinson's disease as the condition. The recorded enrollment is 45. The study is listed as not applicable for phase. Its recorded start is 2015-08, and primary completion is dated 2017-08-16.

The brief description separates the work into two phases. Phase 1 involved in-depth gait analysis using the Computer Assisted Rehabilitation Environment (CAREN), a virtual reality system with integrated 3-D motion capture. The stated purpose was to characterize gait and postural control under specific dual-task conditions. The project description says Phase 1 involved 15 individuals. Phase 2 was described as the clinical translation of those findings, with N=20 and two intervention groups: a dual-task clinical group and a single-task group. Each group was described as including N=10.

The interventions were behavioral. The dual-task group performed activities simultaneously; the single-task group performed motor and cognitive activities individually. Both were described as exercising 3x/week for 8 weeks. The record says outcomes were assessed at the beginning and end of the intervention to evaluate feasibility and efficacy. The primary outcome timeframe also lists an assessment at end of treatment +4 weeks for Phase 2.

The registry identifies single masking but does not report who was masked. The method used to generate the random allocation, allocation concealment, and any stratification are not reported in the registry record. The record does not report a protocol-level sample-size justification or details of the statistical plan. Although the study is marked completed, completion status alone does not supply evidence about the intervention's outcomes.

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.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Two participants (one in Phase 1 and one in Phase 2) were unable to complete the required cognitive assessments, and thus were excluded from all analyses.

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: Two participants (one in Phase 1 and one in Phase 2) were unable to complete the required cognitive assessments, and thus were excluded from all analyses.

6. Primary Endpoint

The registry lists the primary outcome as Step Length During Gait, measured over Phase 1: baseline; Phase 2: baseline, end of treatment (8 weeks), and end of treatment +4 weeks.

The primary endpoint was step length during gait, expressed in meters. It was defined as the average distance from heel strike of the less affected leg to heel strike of the more affected leg. The record states that higher values indicate a longer step length.

Step length is a continuous measure of walking performance. In general, continuous outcomes retain information about the measured amount rather than reducing it to a category. A mean can describe the average observed step length, while a standard deviation describes how much individual measurements vary around that average. The registry identifies the outcome parameter as a mean and its dispersion as a standard deviation, but does not report the numerical means or standard deviations.

The outcome was planned for different assessment schedules across the phases. Phase 1 included baseline measurement. Phase 2 included baseline, end of treatment (8 weeks), and end of treatment +4 weeks. Those time points could address different descriptive questions, such as the starting measurement, the measurement at treatment completion, and the later measurement. However, the registry does not report the results at any of these times or specify a single primary contrast among them. The record therefore supports understanding what was intended to be measured, but not the observed change, between-group difference, or uncertainty around either.

The record notes that two participants could not complete the required cognitive assessments and were excluded from all analyses. It does not explain whether or how this exclusion affected the step-length endpoint beyond that stated exclusion.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a randomized, parallel-group study with single masking. In general, randomization assigns participants to study groups using a chance-based process, which is intended to support a fair comparison by reducing systematic differences at assignment. A parallel design means groups receive their assigned approaches during the same study period rather than crossing over between interventions. The record does not report the randomization method, concealment procedures, or the identity of the masked party, so those aspects cannot be evaluated from the registry entry.

What does a mean and standard deviation describe?

The primary outcome is continuous and is summarized in the registry as a mean with standard deviation. In general, the mean describes the central average of measurements, while the standard deviation describes their spread around that average. These quantities answer different questions: the mean concerns the average level, and the standard deviation concerns variation among measurements. Neither alone establishes a treatment effect. To compare groups, readers would need the reported group results and an appropriate estimate of the contrast, ideally with its uncertainty. Numerical means and standard deviations are not reported in the registry record.

Why does timing matter?

Phase 2 lists baseline, end of treatment (8 weeks), and end of treatment +4 weeks. In general, baseline measurements describe starting status, while later measurements can describe outcomes during or after an intervention. A comparison can be framed around the final measurement, change from baseline, or differences in change between groups; these are not interchangeable analytical choices. The statistical plan identifying the intended comparison is not reported in the registry record. Phase 1 is described as a gait-characterization phase with a baseline timeframe, so it should not automatically be treated as the same intervention comparison as Phase 2.

What can a confidence interval tell readers?

In general, a confidence interval gives a range of values compatible with an estimate under the method used. A narrow interval indicates greater precision than a wide interval, while both the estimate and interval are needed to understand the direction and plausible size of an effect. A confidence interval does not remove design limitations or establish clinical importance by itself. No confidence interval or treatment-effect estimate is reported in the registry record, so precision cannot be assessed for the study's primary outcome.

Why can variability affect analysis?

General statistical methods account for outcome variability when estimating uncertainty. If observations vary more than a model assumes, standard errors and tests based on that model may not describe uncertainty well. For count outcomes, over-dispersion means variation exceeds what a simple count model expects; methods that account for it may be needed. The primary endpoint is continuous rather than a count, and the registry does not report a model or evidence of over-dispersion. This general concept should not be mistaken for a claim that over-dispersion occurred in this study.

What does the registry's analysis status mean?

The record lists zero analyses. That indicates no analyses are posted in the registry record; it does not establish that investigators performed no analysis outside the registry. No p-value, model specification, covariate adjustment, handling of repeated measurements, or inferential method is reported in the registry record. The statistical plan, including any interim analyses, is also not reported in the registry record.

The record includes a sample-size planning illustration based on an observed effect, with stated assumptions of a two-sided significance level of 0.05, equal allocation, and a normal approximation. Such planning illustrations are not observed power and do not describe the trial's own sample-size justification. A protocol-level sample-size justification is not reported in the registry record. The planning assumptions do not supply missing outcome results or resolve the absence of a posted analysis.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists several outcome domains and gives multiple time points for the primary step-length outcome in Phase 2. When a study considers several outcomes, time points, or comparisons, multiplicity can arise: the more statistical questions examined, the greater the chance that an apparently notable result occurs by chance if each is treated as an independent confirmatory test. General approaches include prespecifying a primary contrast, adjusting inference for multiple testing, or clearly labeling secondary analyses as exploratory. The registry record does not report a multiplicity strategy or identify a single comparison for the primary outcome.

The record identifies five secondary outcome names: the 2 Minute Walk Test, Quality of Life in Neurological Disorders Questionnaire, Activities-specific Balance Confidence Scale, Trail Making Test, and Reaction Time. Their inclusion describes planned measurement domains, not reported findings. The analyses count is zero, and numerical results for these outcomes are not reported in the registry record. Whether all were assessed, analyzed, or treated as confirmatory is not reported in the registry record.

The primary outcome description states that two participants, one in Phase 1 and one in Phase 2, could not complete the required cognitive assessments and were excluded from all analyses. The registry does not report the analysis population beyond this statement, the amount or pattern of missing outcome data, or whether any other participants had incomplete measurements. It also does not report an imputation method, sensitivity analysis, or comparison of included and excluded participants.

In general, missing-data methods depend on why measurements are missing and what information remains available. Excluding participants can affect interpretation if the people excluded differ from those analyzed in ways related to the outcome. This is a general concern, not evidence that such a bias occurred. Because the registry gives no outcome estimates and little detail about missingness, the potential effect of the stated exclusions cannot be quantified.

11. Safety Results

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

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

Most frequent non-serious adverse event terms

The registry lists serious adverse events as zero in Phase 1, Phase 2: Dual Task, and Phase 2: Single Task. It separately lists other adverse events as one in Phase 1, one in Phase 2: Dual Task, and zero in Phase 2: Single Task. Deaths are listed as zero in each of those groups. These are the posted counts; they are not measures of treatment effect and do not by themselves establish a difference in safety between groups.

The record gives the numbers at risk for the listed event categories as 24 for Phase 1, 10 for Phase 2: Dual Task, and 11 for Phase 2: Single Task. The adverse-event section does not provide descriptions of the non-serious events, their timing, severity, relationship to intervention, or the method used to collect them. Serious-event terms are not listed. The event figures should therefore be read as registry entries with limited clinical and statistical detail, rather than as a complete account of each event.

In general, an observed count depends on the number of participants monitored and the duration and completeness of follow-up. The registry does not report additional information needed to assess those factors or to compare event rates with precision. The listed counts do not support a conclusion that one approach is safer or less safe.

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

The record establishes that a completed randomized study was registered to examine gait and other outcomes in people with Parkinson's disease. It describes two related phases: gait characterization and clinical comparison of dual-task with single-task exercise. It also defines step length and names the other outcome domains. These details clarify the study's aims and planned measurements.

What the record does not establish is the effect observed. Numerical results for step length and the secondary outcomes are not reported in the registry record. There is no posted estimate of the difference between groups, no reported uncertainty interval, and no analysis result. Thus, the study entry cannot show whether the groups differed, how large any difference was, or how precisely it was estimated.

In general, an estimate's statistical precision and its practical importance are distinct. Precision concerns uncertainty around an estimate; practical importance concerns whether the estimated difference matters in context. Neither can be evaluated without outcome estimates and relevant interpretation. The registry does not report a threshold for an important step-length difference or other contextual criteria.

The study's randomized design is relevant to how a comparison could be interpreted, but design labels alone do not guarantee that all sources of bias or uncertainty are resolved. The record lacks details about allocation procedures, masking, the analysis plan, multiplicity, and handling of missing data. The stated exclusions for incomplete cognitive assessments also bear on how the analyzed population was defined, but further details are not reported in the registry record.

Accordingly, the defensible conclusion is limited: the registry describes the research question, interventions, outcome schedule, and some event counts, but it does not provide the results needed to draw an efficacy or comparative safety conclusion. This is a statement about what the registry record reports, not a claim about analyses or findings that may exist elsewhere.

13. Why This Trial Matters Statistically

This study raises several statistical issues that are common in rehabilitation research. Its primary outcome is a continuous gait measure, while its stated aims span motor, cognitive, and quality-of-life domains. That breadth makes it important to distinguish the primary endpoint from secondary outcomes and to identify which comparisons are intended to answer confirmatory questions. The registry names outcomes but does not report a statistical plan or multiplicity approach.

The project also combines a gait-characterization phase with an intervention phase. These phases have different stated purposes, so a statistical interpretation should not treat them as interchangeable. Phase 1 was intended to describe gait and postural control under specific dual-task conditions; Phase 2 was intended to translate those observations into a clinical intervention. The registry does not report analyses that connect the two phases or quantify the treatment comparison.

Repeated assessment is another relevant issue. Phase 2 includes baseline and follow-up measurements, which raises the general question of whether analysis should compare endpoint values, changes, or trajectories over time. Those choices can lead to different estimates and require clear specification. The intended approach is not reported in the registry record.

Finally, the record illustrates why completion status, outcome definitions, and safety counts should not be mistaken for evidence of an effect. Without posted estimates and their uncertainty, readers cannot assess the magnitude, precision, or robustness of a comparison. Clear reporting of analysis populations, missing-data handling, and planned contrasts would be necessary for a fuller statistical appraisal.

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 main limitation of the registry record for statistical interpretation is the absence of posted outcome analyses. Although the study is marked completed and the primary endpoint is defined, numerical results are not reported in the registry record. The record lists zero analyses, leaving no treatment-effect estimate, interval, or test result to assess.

The study description covers two phases with different aims and assessment schedules. The record does not explain how results from those phases were intended to be combined or kept analytically distinct beyond their descriptions. The Phase 2 primary outcome has multiple listed time points, but the specific contrast designated for inference is not reported in the registry record.

Details needed to evaluate risk of bias and reproducibility are also limited. The record identifies randomization and single masking, but the allocation procedure, concealment, and identity of the masked party are not reported. The statistical plan, covariate adjustments, interim analyses, and sample-size justification are not reported in the registry record.

The primary outcome description states that two participants who could not complete required cognitive assessments were excluded from all analyses. Further details about missing outcome data, other exclusions, and analysis populations are not reported. The record also does not describe whether all named secondary outcomes were collected or how multiple outcomes were addressed.

Safety information is limited to event counts and numbers at risk. Event descriptions, timing, severity beyond the serious/non-serious distinction, attribution, and follow-up completeness are not reported. These limitations restrict both outcome interpretation and appraisal of the study's statistical methods; they do not establish that the study was conducted improperly.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: The Effects of Dual Task Training in Individuals With Parkinson's Disease — NCT02538029.
• Registry record last updated 2019-05-03; status last verified 2019-02.
• Results first posted 2019-05-03.
• 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

NCT02538029 is listed as a completed, randomized, single-masked, parallel study sponsored by The Cleveland Clinic. The registry describes Phase 1 gait analysis and Phase 2 comparison of dual-task and single-task exercise in people with Parkinson's disease. Both intervention groups were described as exercising 3x/week for 8 weeks.

The primary outcome was mean step length during gait, measured in meters, with assessment times specified for each phase. The registry also names secondary outcomes involving walking, quality of life, balance confidence, cognitive testing, and reaction time. It reports zero posted analyses, and numerical outcome results are not reported in the registry record. Serious adverse event counts are listed as zero in each group; other adverse event counts and deaths are also recorded. The absence of posted results prevents assessment of the intervention comparison's magnitude or precision.