This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Low Frequency Deep Brain Stimulation of the Subthalamic Nucleus in Parkinson's Disease (NCT03204526), a na na study. The primary outcome is Mean Reaction Time for Computerized Color Naming Stroop Task.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT03204526 |
| Phase | NA |
| Condition | Parkinson Disease, Cognitive Impairment |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 15 |
| Arms in the primary outcome | n/a |
| Lead sponsor | University of California, Davis |
| Results posted | Yes |
2. Clinical Question
Population
The study concerns patients with advanced Parkinson’s disease and cognitive impairment. The registry describes participants as people who had already undergone deep brain stimulation (DBS) implantation surgery as part of routine care for motor manifestations of Parkinson’s disease. Enrollment was 15. The record does not report further eligibility details or describe the characteristics of the participants who enrolled.
Intervention
The intervention was temporary low-frequency deep brain stimulation of the subthalamic nucleus. The brief summary specifies the ventral subthalamic nucleus. The study sought to determine the effects of this stimulation on cognition in people whose DBS implants had been placed for motor care. Details such as stimulation settings and the precise schedule of assessments are not reported in the registry record.
Comparator
The record describes a single-group study and lists no like-for-like control arm. Allocation is recorded as not applicable, and masking is listed as none. Consequently, the registry information does not establish a randomized comparison between low-frequency stimulation and another stimulation condition, or between stimulation and no stimulation. The analysis structure used to assess changes within participants is not reported in the registry record.
Primary question
The primary outcome was mean reaction time, in seconds, on a computerized color-naming Stroop task, with a timeframe of 2 days. The study question was whether temporary low-frequency stimulation was associated with a change in cognitive task performance. The registry explains that the Stroop test assesses the ability to inhibit interference between stimulus features. It does not report the reaction-time result, its confidence interval, or a statistical test, so the observed direction, magnitude, and precision cannot be assessed from the registry record.
3. Trial Design
This was a prospective, single-group trial of low-frequency deep brain stimulation in people with advanced Parkinson’s disease. The registry lists enrollment as 15 and status as completed. The study started in 2015-06, and primary completion was recorded as 2019-11. Its stated focus was safety and feasibility of using low-frequency stimulation of the subthalamic nucleus to improve cognitive performance.
Participants had DBS implants placed as part of their routine care for motor manifestations of Parkinson’s disease. The study applied a temporary period of low-frequency stimulation to examine its effects on cognition. The intervention is named as a device intervention; the listed arm is low-frequency stimulation. The registry does not describe a separate control arm, random allocation, or masking. Allocation is marked not applicable, and masking is listed as none.
These features matter when interpreting any apparent change. Without a like-for-like control group, a before-and-after difference, if one were reported, would not by itself distinguish a stimulation effect from other explanations such as changes over time, task familiarity, or variation in measurement. Whether participants were assessed repeatedly, and how any repeated measurements were analyzed, is not reported in the registry record. The record also does not report a protocol for treatment assignment or a detailed account of the stimulation schedule.
The registry identifies four outcome measures and lists no analyses. It names the primary measure as mean reaction time on the computerized color-naming Stroop task, with a 2-day timeframe. It also names secondary measures concerning worsening depression and motor worsening. Results for these outcomes are not reported in the registry record. The listed phase is not applicable. Details of the sample-size rationale and a prespecified statistical analysis plan are not reported in the registry record.
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
| Stage | Low Frequency Stimulation (LFS) |
|---|---|
| STARTED | 15 |
| COMPLETED | 15 |
| NOT COMPLETED | 0 |
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.
| Characteristic | Unit | Low Frequency Stimulation (LFS) |
|---|---|---|
| Participants analysed | 15 | |
| Age, Continuous | Year | 62.18 (SD 6.42) |
| Sex: Female, Male: Female | Participants | 2 |
| Sex: Female, Male: Male | Participants | 13 |
| Race and Ethnicity Not Collected | Participants | — |
| Race and Ethnicity Not Collected | Participants | — |
| Disease Duration | Year | 7.73 (SD 3.38) |
6. Primary Endpoint
The registry lists the primary outcome as Mean Reaction Time for Computerized Color Naming Stroop Task, measured over 2 days.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | 95% Confidence Interval |
| Unit | seconds |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is mean reaction time, measured in seconds, on a computerized color-naming Stroop task. The registry gives a 2-day timeframe and describes the Stroop Color and Word Test as a neuropsychological test used to assess the ability to inhibit cognitive interference. Such interference arises when processing one feature of a stimulus impedes the simultaneous processing of another feature. The registry refers to this as the Stroop Effect.
Reaction time is a continuous measure: it records how long a response takes rather than placing each participant into a category. A mean can summarize the response times within an analysis group or condition. In general, reaction-time tasks are used because they quantify task performance in a way that can be compared across assessments or conditions. The interpretation depends on how the assessments were conducted and analyzed, details not reported in the registry record.
The registry does not report the mean reaction time, a confidence interval, or a comparison between assessments. Therefore, it is not possible to determine from the record whether reaction times changed, how large any change was, or how precisely it was estimated. The stated timeframe alone does not establish the timing of all measurements or the method used to form the reported mean.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record identifies a clinically relevant cognitive performance question, but it does not provide the numerical primary outcome result. It lists mean reaction time on the computerized color-naming Stroop task as the primary endpoint and gives a 2-day timeframe. No mean, confidence interval, test statistic, or p-value is reported. Accordingly, the record does not allow an assessment of the direction or magnitude of the primary outcome, nor of the uncertainty around an estimate.
The study’s single-group design also constrains what any within-study change could establish. The registry does not list a randomized or masked control comparison. Even if a pre-to-post change were available, a single-group comparison would not, by itself, separate an effect of low-frequency stimulation from other changes associated with time, assessment, or the study context. The exact measurement and analysis structure is not reported in the registry record, so it is not possible to say whether the primary analysis used repeated observations or another approach.
The record names secondary outcomes concerning worsening depression using Beck’s Depression Index and motor worsening using the Unified Parkinson’s Disease Rating Scale (UPDRS-III). It does not report their results. The absence of those results in the registry record should not be read as evidence that the outcomes did not change; it means their observed values cannot be evaluated from this record.
The completed status indicates that the registry marks the study as completed. It does not supply evidence about the primary endpoint’s findings. Likewise, the enrollment figure describes study enrollment, not the number of participants with complete data for every outcome. Outcome-specific analysis populations and missing-data information are not reported in the registry record.
In general, a confidence interval communicates the range of estimates compatible with the data and the stated statistical procedure. Without the endpoint estimate and its reported interval, precision cannot be judged. Statistical significance, clinical importance, and reproducibility also cannot be assessed from the outcome information available in the registry record. The defensible reading is therefore limited: the study was designed to examine cognition during temporary low-frequency stimulation, but the posted registry information does not show the primary or secondary outcome results.
9. Statistical Methods Explained
The primary measure is continuous: mean reaction time in seconds on a computerized Stroop task. For a continuous outcome, the mean describes the central level of the measured values. Its interpretation depends on which observations are included and how those observations are grouped. The registry identifies the measure and its unit, but it does not report the actual mean or explain the analysis population used to calculate it.
What does a confidence interval communicate?
The registry specifies a 95% confidence interval as the dispersion measure for the primary outcome. In general, a confidence interval expresses statistical uncertainty around an estimate under the assumptions of the analysis method. A narrower interval indicates greater precision than a wider interval, while the estimate itself indicates the location of the result. The interval is not a guarantee that the true value lies within its bounds. Because the registry record does not report the mean or interval limits, neither the result nor its precision can be interpreted.
What does the study design permit?
The trial is listed as single-group, with allocation marked not applicable and no masking. In general, random allocation to a comparison group can help distinguish intervention effects from factors that affect both groups, while masking can reduce certain forms of expectation-related influence. Those protections are not described for this study. The record does not identify a like-for-like control group or explain whether each participant contributed measurements under more than one stimulation condition. It is therefore not appropriate to assume a particular paired, repeated-measures, or between-group analysis.
A within-participant comparison can be useful in general when measurements are made on the same people under different conditions, because each participant can serve as a reference for their own measurements. However, the registry record does not state that this was the analysis used. Even when repeated measures are collected, changes can reflect factors other than the intervention, and the interpretation depends on timing, task procedures, and the analysis plan.
What can be inferred from the sample-size description?
The registry describes a planning illustration based on an observed effect. It states that this illustration uses a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect to detect expressed as a fraction of the observed effect. Those are assumptions for a hypothetical planning exercise, not a description of the actual single-group trial design. The registry record does not provide numeric planning results or the observed effect needed to interpret such an illustration. These planning assumptions must not be treated as an observed power calculation or as evidence that the trial had a particular ability to detect an effect.
In general, sample-size planning depends on the outcome variability, the effect considered important to detect, the statistical test, and the desired error rates. A planning calculation cannot establish what the trial found. Here, the available record gives the enrollment figure but does not report a sample-size justification, a target effect, or the assumptions used in the original trial design.
How should multiple outcomes be considered?
The registry lists four outcome measures and no analyses. When several outcomes are examined, the chance of at least one apparently notable finding can increase if results are interpreted without accounting for the number of comparisons. General approaches include prespecifying a primary outcome, adjusting for multiple tests, or treating secondary analyses as exploratory. The registry identifies a primary endpoint and names secondary outcomes, but the multiplicity strategy and the analysis plan are not reported in the registry record. No claim about adjustment or the intended status of secondary analyses can therefore be made.
What is missing for a full statistical assessment?
The registry record does not report the primary estimate, its confidence interval, a hypothesis test, or outcome-specific analysis counts. It also does not describe missing-data handling, model specification, covariate adjustment, or diagnostics. General statistical interpretation depends on these details: for example, model assumptions determine whether an estimate and its uncertainty are appropriately characterized. For count outcomes, over-dispersion can matter when observed variability exceeds what a simpler count model assumes; however, the primary outcome is continuous, and the registry does not report an analysis model for any outcome. No specific model or diagnostic procedure should be inferred.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists four outcome measures: the primary mean reaction time on the Stroop task and secondary measures concerning worsening depression and motor worsening. It reports no analyses. Although a primary outcome is identified, the registry record does not report whether the secondary outcomes were treated as confirmatory or exploratory, whether any multiplicity adjustment was planned, or how multiple tests would be interpreted.
In general, examining several outcomes creates multiple opportunities for a result to appear noteworthy by chance. A prespecified outcome hierarchy or an adjustment procedure can help control that issue. The presence of a named primary endpoint does not establish that an adjustment was used for secondary outcomes. The analysis plan is not reported in the registry record, so no such procedure can be attributed to this study.
The record does not give outcome-specific numbers analyzed, explain whether any observations were missing, or state how missing measurements were handled. Enrollment does not necessarily indicate that complete outcome data were available for every participant. It is also not reported whether the analysis used all enrolled participants or a subset defined by another rule. No analysis population can be inferred from the registry information.
These omissions limit assessment of both bias and precision. Missing outcome data can affect an estimate if the likelihood of missingness is related to participants’ outcomes or characteristics; general methods for handling missing data rely on assumptions that should be stated. Without results, analysis counts, and a missing-data approach, neither the sensitivity of the findings nor the robustness of any estimate can be evaluated. The registry record does not report these details.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Low Frequency Stimulation (LFS) | 0 | 15 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Low Frequency Stimulation (LFS) | 0 of 15 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Low Frequency Stimulation (LFS) | 0 of 15 |
For the low-frequency stimulation group, the registry lists 15 participants at risk for serious adverse events and records zero serious adverse events affecting participants. It also records zero deaths. The registry lists 15 at risk for other adverse events and records zero participants affected in that category. No serious adverse event terms are listed.
These are registry safety counts, not a complete description of how safety was assessed. The record does not report the event-collection procedures, observation period for adverse events, definitions used, or whether any events led to withdrawal or changes in stimulation. It also does not provide detailed event-level information beyond the listed counts.
Zero recorded events in this study does not establish that the intervention has no risk. In general, safety findings depend on the number of people observed, the duration and completeness of follow-up, and how events are collected and classified. With no comparison group listed, the counts also do not provide a controlled estimate of whether events were more or less common under stimulation. The appropriate interpretation is limited to what the registry records: no serious adverse events, deaths, or other adverse events affecting participants are listed for this group.
12. What the Result Does, and Does Not, Mean
The registry record describes a prospective study of temporary low-frequency stimulation of the subthalamic nucleus, focused on cognitive performance in people with advanced Parkinson’s disease. It identifies a primary Stroop reaction-time measure and describes the cognitive process that the task is intended to assess. It also records a completed study and lists enrollment as 15.
However, the registry record does not report the primary outcome result or results for the secondary outcomes. There is no reported mean reaction time, confidence interval, or statistical test. As a result, the record cannot establish whether task performance changed, the size or direction of a change, or the precision of an estimate. It also cannot support a conclusion about the secondary measures concerning depression or motor worsening.
The design is single-group, with no randomized control arm listed and no masking. In general, a change observed in one group over time is not enough by itself to attribute that change to an intervention. A controlled comparison can help address alternative explanations, but no such comparison is described in the registry record. The precise assessment sequence and analysis structure are also not reported.
The listed absence of recorded adverse events is a description of the registry safety counts, not proof that no risk exists. The record does not give the detail needed to assess the completeness of event ascertainment or to compare safety with another condition.
Thus, the registry information establishes what the study set out to examine and provides limited design and safety details, but it does not provide the outcome evidence needed to judge the observed cognitive results. This distinction is important: a study’s purpose and completion status do not substitute for reported estimates and their uncertainty.
13. Why This Trial Matters Statistically
This trial raises a statistical question about measuring cognitive task performance in a clinical setting where participants already have DBS implants for motor care. Its primary endpoint is a continuous reaction-time measure from a Stroop task, and the registry links that task to the ability to inhibit cognitive interference. That makes the endpoint relevant to the study’s stated cognitive focus, while also requiring careful interpretation of what a task-based measure represents.
The single-group design is important statistically because it limits causal interpretation. A within-group change, if reported, could be consistent with an intervention effect, but without a like-for-like control comparison it would also remain compatible with other explanations. The registry record does not report the analysis structure, so it is not possible to assess whether repeated observations or another comparison was used.
The record also illustrates why an endpoint definition and an outcome result are different kinds of information. It gives the measure, unit, timeframe, and confidence-interval type, but not the estimate or interval. Without those results, readers cannot evaluate magnitude, direction, precision, or statistical evidence. The listed secondary outcomes further make it important to know how multiple analyses were planned and interpreted; that information is not reported.
Finally, safety counts are informative only within their scope. The record lists no adverse events affecting participants, but does not report event-collection details or a comparison group. The statistical value of the study record therefore lies in its description of the question and design, while its ability to answer that question is limited by the absence of posted outcome analyses.
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.
Several trial-specific limitations follow from the registry information. First, the design is described as single-group, and no randomized comparison arm is listed. This limits the ability of any observed change to distinguish a stimulation effect from other changes over time or from the process of repeating a cognitive task. The registry does not report whether participants completed more than one assessment condition or how observations were compared.
Second, the outcome results are not reported. The primary Stroop reaction-time estimate and its confidence interval are absent, as are the results for the listed secondary outcomes. The record lists no analyses, so there is no basis for evaluating effect size, precision, statistical evidence, or outcome-specific analysis populations.
Third, the registry does not report key analysis details, including the statistical model, missing-data handling, multiplicity strategy, or prespecified analysis plan. These details matter for judging whether estimates are robust and whether multiple outcomes were interpreted appropriately. The sample-size description is a planning illustration with assumptions that include two-arm equal allocation, rather than a report of the actual single-group design; numeric planning outputs and the trial’s own sample-size justification are not reported.
Finally, the record provides limited safety detail beyond counts. Event definitions, ascertainment procedures, and relevant follow-up information are not reported. The enrolled population is described broadly, and further participant characteristics and eligibility details are not reported in the registry record. These limitations restrict interpretation of both the study’s generalizability and the meaning of its safety information.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Low Frequency Deep Brain Stimulation of the Subthalamic Nucleus in Parkinson's Disease — NCT03204526.
- Registry record last updated 2021-06-23; status last verified 2021-06.
- Results first posted 2021-06-23.
- 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.
Continue through the Clinical Biostats statistical pathway
Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
18. Record Summary
The registry record describes a completed prospective, single-group study of temporary low-frequency deep brain stimulation of the subthalamic nucleus in patients with advanced Parkinson’s disease. Enrollment was 15. The primary outcome was mean reaction time in seconds on a computerized color-naming Stroop task, with a 2-day timeframe. The registry explains that the test assesses inhibition of cognitive interference.
Allocation is listed as not applicable, and masking as none. The record names secondary outcomes concerning worsening depression and motor worsening. It reports no analyses and does not provide primary or secondary outcome results. For the low-frequency stimulation group, it lists zero serious adverse events, zero deaths, and zero participants affected by other adverse events. The registry does not report the statistical analysis plan, missing-data handling, or detailed safety ascertainment methods.