Neurobiological Drivers of Mobility Resilience: The Dopaminergic System - Placebo-Controlled Arm: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Neurobiological Drivers of Mobility Resilience: The Dopaminergic System - Placebo-Controlled Arm (NCT06219915), a randomized phase 1, phase 2 study. The primary outcome is Average Gait Speed.

2. Clinical Question

The study focuses on the proposed relationship between dopamine and walking performance in older adults with parkinsonian signs. Its rationale describes age-related walking changes and prior observations about dopamine and walking, but those background statements are not outcomes of this randomized comparison. The trial’s primary endpoint is average gait speed. Other listed outcomes concern cognitive rating and performance on the Stroop Color Word Stepping Test.

The registry describes the trial as randomized, quadruple-masked, and parallel-group. The record reports enrollment of 13, but does not provide outcome results or explain the analysis population. Consequently, the clinical question can be described from the trial design, while the size, direction, and precision of any primary treatment difference cannot be assessed from the registry record.

3. Trial Design

This is a completed randomized, parallel-group study sponsored by the University of Michigan. The registry lists both phase 1 and phase 2. The start date is 2024-03-15, and the primary completion date is 2024-05-30. The record lists enrollment of 13 and describes the study as quadruple-masked. It does not specify which groups of people were masked, or explain how masking was maintained.

Participants were assigned to carbidopa monotherapy and carbidopa-levodopa or to placebo. The active-treatment description begins with carbidopa 25 mg taken three times per day for 3 days. On day four, it describes adding carbidopa-levodopa 25/100 mg, and on day seven, increasing the amount to 1.5 tablets. The description ends mid-sentence, so the complete medication schedule is not reported in the registry record. The placebo description likewise begins with a placebo tablet three times per day, adds a separate placebo tablet on day four, and describes an increase on day seven; its full schedule is also not reported.

The primary endpoint is average gait speed, measured at baseline and post-intervention, 7-13 days after beginning the supplement. Measurements are described as using wearable sensors and a sensor mat. Three secondary outcomes are listed: the Parkinson's Disease Cognitive Rating Scale Score, the mean number of incorrect responses on the Stroop Color Word Stepping Test, and mean reaction time during that test.

The registry identifies 4 outcome measures, but reports no analyses. It does not state a primary-outcome estimate, a comparison between groups, a confidence interval, or a p-value. The enrollment figure describes the trial record and should not be read as evidence about the precision or reliability of an effect estimate; no such estimate is reported.

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: Participants were considered "enrolled" once they signed a consent form. While thirteen participants were consented and therefore enrolled, two failed their screening post-consent. Eleven were randomized and participated in the study.

Overall 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.

6. Primary Endpoint

The registry lists the primary outcome as Average Gait Speed, measured over Baseline and post-intervention (7-13 days after beginning supplement).

The primary endpoint is average gait speed, a continuous measure recorded in meters per second. The registry describes measurements at baseline and post-intervention, with the latter scheduled 7-13 days after beginning the supplement. Wearable sensors and a sensor mat are named as measurement methods. The endpoint description does not report the precise processing rules used to derive the average, or say how measurements from the two devices were combined.

Gait speed is used in this study to quantify walking performance. As a continuous measure, it can reflect both the magnitude and direction of change rather than classifying participants into categories. A comparison of post-intervention values, or of change from baseline, could describe whether the groups followed different average patterns. Which comparison was intended for the primary analysis is not reported in the registry record.

General statistical context: a mean summarizes the central value of a continuous measure across observations. A standard deviation describes how spread out individual measurements are around that mean; it is not a measure of uncertainty in the mean itself. Estimating a treatment-group difference with adequate precision requires the group summaries and an analysis that accounts for the trial design and the measurements being compared.

The registry names the mean and standard deviation as the summary form for this outcome. It does not post either group’s gait-speed summary, a change estimate, or an uncertainty interval. Therefore, the endpoint’s clinical and statistical interpretation remains limited to what it was designed to measure and when the measurements were scheduled.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does randomization contribute?

The registry classifies the study as randomized, which means assignment to the parallel groups was intended to use a random process. General statistical context: random assignment can help balance prognostic characteristics across groups on average and supports interpreting a between-group comparison as an estimate of the effect of assignment. It does not guarantee that groups are identical, especially in a small trial. The method used to generate the allocation sequence, conceal assignments, or handle deviations is not reported in the registry record.

What does quadruple masking tell readers?

The registry labels masking as quadruple. This signals that masking was recorded as part of the study design, but the record does not identify the four groups or roles that were masked. It also does not describe how medication and placebo were made indistinguishable, whether masking was assessed, or whether it was maintained. The study summary calls the study double-blinded, while the design field records quadruple masking; further detail resolving the terminology is not reported in the registry record.

How should a continuous endpoint be summarized?

Average gait speed is continuous and is expressed in meters per second. The registry identifies the mean as the summary measure and the standard deviation as the dispersion measure. General statistical context: the mean conveys the center of a distribution, while the standard deviation describes how far individual values tend to vary around that center. These describe different features of the data. A standard deviation is not a standard error or confidence interval and does not, by itself, quantify the precision of a treatment comparison.

A complete report would ordinarily make clear the group summaries, the comparison being estimated, and uncertainty around that estimate. For a baseline and post-intervention measure, analysts may use different reasonable approaches, including comparing post-intervention values while accounting for baseline or comparing change from baseline. The record does not report the primary analysis method, so readers cannot determine which approach underlies a result.

What would a confidence interval add?

General statistical context: a confidence interval communicates uncertainty around an estimated effect under the chosen statistical model. It helps readers judge which effect sizes remain compatible with the observed data and method. The interval’s width is informative about precision, while its position relative to no difference can be relevant to statistical testing. Neither property replaces judgment about clinical importance. No confidence interval for the primary endpoint is reported in the registry record.

Why might variability and model choice matter?

Gait measurements can vary among people and across measurements. General statistical context: greater variability tends to make a group comparison less precise if other features are unchanged. Repeated measurements also require attention to how within-person association is handled. The registry does not report the observed standard deviations, the correlation between baseline and post-intervention values, or the statistical model used. There is therefore no basis in the record to assess those aspects of the analysis.

General statistical context: over-dispersion is a concern for some count-data models when the observed variation exceeds what a basic model assumes. It is not a central feature of a mean gait-speed outcome, which is continuous. The record lists secondary outcomes involving counts of incorrect responses, but does not report their distributions or analyses; whether over-dispersion was relevant to those outcomes cannot be determined from the registry record.

What do the planning assumptions mean?

The registry describes planning illustrations based on the observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. It says that the effect to detect is a stated fraction of the observed effect, and that sample-size illustrations for non-time-to-event outcomes are expressed as participants per arm for 80% or 90% power. These are planning assumptions, not results from an observed trial analysis. The posted record does not report an observed primary effect estimate or the numerical planning illustrations, so no sample-size value or effect size can be interpreted from this information.

General statistical context: power is a design quantity describing the probability of detecting a specified effect under assumptions if that effect is true. It is not a measure of whether an observed result is reliable, and a planning illustration is not observed power. When a planning calculation uses an observed effect, its value can depend on the estimate used as the planning input. Here, the registry does not give the effect estimate needed to evaluate such an illustration.

What analysis details remain unknown?

The registry reports 0 analyses and does not state whether the primary comparison used an intention-to-treat population, a per-protocol population, or another analysis set. It does not report how missing measurements were handled, whether outliers or protocol deviations were addressed, or whether the treatment effect was adjusted for baseline values. The significance level in the planning assumptions should not be mistaken for confirmation of the test used for the primary outcome. The inferential statistical plan is not reported in the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome, average gait speed, and three secondary outcomes: the Parkinson's Disease Cognitive Rating Scale Score, mean number of incorrect responses on the Stroop Color Word Stepping Test, and mean reaction time during that test. It also identifies 4 outcome measures overall. The record does not describe a multiplicity strategy, such as a hierarchy of outcomes or an adjustment to account for multiple statistical tests. Because no outcome analyses are reported, it is not possible to determine which tests, if any, were carried out or how their results were interpreted.

General statistical context: when many outcomes or comparisons are tested, the chance of at least one apparently unusual result can increase unless the analysis plan addresses multiplicity. Adjustments may affect the threshold for interpreting results or the uncertainty estimates. Whether such adjustments are appropriate depends on the study’s aims and prespecified plan; that plan is not reported in the registry record.

Missing-data handling and analysis populations are also not reported. The record does not state how many participants completed each gait assessment, whether any endpoint measurements were unavailable, or what methods would be used for missing values. It does not identify whether all randomized participants were included in an analysis or whether exclusions occurred. These omissions matter because the analyzed population and missingness approach can influence the meaning and precision of an estimate.

General statistical context: missing measurements can reduce precision and may bias results if their absence is related to participant characteristics or outcomes. The appropriate response depends on why data are missing and on the analysis plan. No missing-data assumptions or sensitivity analyses are reported in the registry record, so their adequacy cannot be evaluated.

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 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry reports serious adverse events in 0 participants in the carbidopa monotherapy and carbidopa-levodopa group, with 6 at risk, and 0 participants in the placebo group, with 5 at risk. Deaths are reported as 0 in each group. Other adverse events are reported in 3 participants in the active-treatment group, with 6 at risk, and 3 participants in the placebo group, with 5 at risk.

These are reported counts, not estimates of comparative risk. No serious adverse-event terms are listed. The record does not provide descriptions of the other adverse events, their severity, timing, duration, or whether investigators considered them related to study treatment. It also does not explain the distinction used between serious and other adverse events beyond reporting them in separate categories.

General statistical context: a zero count in a group does not establish that an event is impossible, and counts from small groups can be imprecise. The event counts should be read alongside the number at risk and the limited reporting detail. They do not establish a causal relationship between treatment and any event, and they do not substitute for the missing primary-outcome analysis.

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

The registry record establishes that a randomized, placebo-controlled study of a dopaminergic regimen and average gait speed was completed. It describes a baseline and post-intervention assessment, gives a post-intervention timeframe of 7-13 days after beginning the supplement, and lists gait speed as the primary outcome. It also documents several secondary outcomes and reports adverse-event counts.

It does not establish whether the active-treatment group had a higher, lower, or similar average gait speed compared with placebo. No group means, treatment-effect estimate, confidence interval, or p-value for gait speed is reported. The record therefore cannot show the magnitude or precision of a primary-outcome difference. A completed status is not a substitute for an outcome analysis, and the absence of posted results should not be interpreted as a finding of no effect.

Likewise, the secondary outcomes are named but their findings are not reported. The background rationale discusses walking, aging, and dopamine, but those statements do not provide results from this randomized comparison. The record does not describe whether any observed changes were clinically important or how they might relate to participants’ everyday function.

General statistical context: a statistically detectable difference, if reported, would not automatically establish that the difference is meaningful to patients. Interpretation would depend on the effect estimate, uncertainty, measurement properties, and clinical context. None of those primary-outcome results is available in the registry record. The reported safety counts are also limited: they do not detail event types or attribution and cannot alone characterize the overall balance of benefits and harms.

The most defensible interpretation is therefore descriptive. The record outlines the trial design and reports limited safety counts, but it does not report the analyses needed to answer the primary comparative question. Any conclusion about the relative effect of the medication regimen on average gait speed would go beyond the information reported in the registry record.

13. Why This Trial Matters Statistically

This trial is statistically notable for linking a continuous functional measure to a randomized, placebo-controlled comparison. Average gait speed can be summarized on its original measurement scale, and the design includes a baseline and post-intervention assessment. These features make the intended comparison understandable, but interpretation still depends on the reported analysis and its uncertainty.

The registry record also illustrates the difference between a completed study and a fully interpretable result. It records enrollment, group design, endpoint timing, and adverse-event counts, yet does not report primary-outcome estimates or analyses. Without those results, readers cannot judge effect magnitude, precision, or compatibility with clinically meaningful differences. This gap is especially important when a record’s background rationale is detailed: rationale is not a replacement for comparative outcome evidence.

General statistical context: small studies can be useful for characterizing feasibility, measurement procedures, or early signals, but estimates from small samples may be uncertain. The registry lists enrollment of 13; it does not report the actual analysis population or variability of the primary outcome. It is not possible to quantify precision or determine what effects the study could reliably distinguish from the record alone.

The record’s planning assumptions also highlight why design illustrations should be distinguished from observed evidence. Sample-size calculations based on an observed effect are planning exercises; they do not constitute evidence that the effect is established, and they are not observed power. Since the registry does not report the observed gait-speed effect or numerical planning illustrations, those considerations cannot be assessed further.

Overall, the statistical importance lies in recognizing what the design can ask and what the posted record can answer. It describes a clear randomized comparison and a continuous primary endpoint, but leaves the central treatment-effect estimate and its uncertainty unreported.

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 primary limitation for interpreting this trial is that the registry record reports no outcome analyses. It contains no group-level gait-speed summaries, treatment-effect estimate, confidence interval, or significance test. This prevents assessment of the primary comparison’s direction, size, or precision. The record is marked completed, but does not provide results that resolve the research question.

Important analysis details are also absent. The record does not identify the statistical model, the exact primary comparison, the analysis population, or the handling of missing measurements. It does not explain whether the baseline measurement was incorporated into the analysis or how protocol deviations were addressed. These are not reported in the registry record, so the robustness of a primary estimate cannot be assessed.

The intervention descriptions are incomplete in the registry record. The active-treatment and placebo schedules include dose changes on day seven, but the text ends before the full regimen is described. The record also does not provide detailed eligibility criteria or clarify which roles were masked under the quadruple-masking designation. These gaps limit the ability to reproduce the design from the registry description alone.

The available enrollment figure does not reveal how many participants contributed data to each outcome. The registry does not report outcome-specific completeness, the variability of gait speed, or the number of participants included in any analysis. No inference about precision should be made from enrollment alone.

Safety reporting is similarly limited. The registry gives counts for serious and other adverse events and deaths, but does not describe event types, timing, severity, or attribution. Finally, although secondary outcomes are listed, neither their analyses nor a multiplicity approach is reported. These limitations make the record useful for describing the registered design and reported counts, but insufficient for a full efficacy or safety assessment.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Neurobiological Drivers of Mobility Resilience: The Dopaminergic System - Placebo-Controlled Arm — NCT06219915.
• Registry record last updated 2025-06-17; status last verified 2025-06.
• Results first posted 2025-06-17.
• 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

The registry describes a completed, randomized, quadruple-masked, parallel-group study sponsored by the University of Michigan, with enrollment of 13. The listed phases are phase 1 and phase 2. The study compares carbidopa monotherapy followed by carbidopa-levodopa with placebo in older persons with parkinsonian signs.

Average gait speed, measured in meters per second, is the primary outcome. The planned assessments are at baseline and post-intervention, 7-13 days after beginning the supplement, using wearable sensors and a sensor mat. Three secondary outcomes are listed: a Parkinson's disease cognitive rating score, incorrect responses on a Stroop Color Word Stepping Test, and reaction time during that test.

The record reports no outcome analyses or primary treatment-effect estimate. Serious adverse events and deaths are reported as 0 in both groups; other adverse events are reported in 3 participants in each group. The event details are limited, and the registry record does not report a statistical analysis plan, missing-data approach, or multiplicity strategy.