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 Deep Brain Stimulation (DBS) Frequency Effects on Gait in Parkinson's Disease(PD) (NCT00993291), a na phase 1, phase 2 study. The primary outcome is Change in Stride Length From Baseline.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00993291 |
| Phase | Phase 1, Phase 2 |
| Condition | Parkinson Disease |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | Double |
| Enrollment | 20 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Vanderbilt University |
| Results posted | Yes |
2. Clinical Question
Population
People with Parkinson disease who had noted a change in their walking. The registry describes bilateral subthalamic nucleus deep brain stimulation (STN-DBS); further eligibility criteria are not reported in the registry record.
Intervention
A frequency change to 60 Hz, evaluated after the setting had been in place for one hour.
Comparator
The primary outcome description compares stride length after a frequency change with the participant’s baseline DBS frequency. A frequency change to 130 Hz is also listed as an intervention, but the registry does not describe the sequence or details of comparisons between settings.
Primary question
How does stride length change from baseline after DBS frequency is changed for one hour? The registry’s stated hypothesis concerns improved gait at 60 Hz and no worsening of the Unified Parkinson’s Disease Rating Scale (UPDRS), but outcome results are not reported in the registry record.
The clinical question is about short-term changes in gait under different stimulation-frequency settings. The registry identifies change in stride length from baseline as the primary outcome, with gait velocity and time to walk 14 meters listed as secondary outcomes. Its brief summary also describes the investigators’ hypothesis about the Stand walk sit test and UPDRS. A hypothesis is a proposed expectation, not evidence that the outcome occurred.
The record does not explain whether participants were assessed at both changed frequencies, how any order was selected, or how measurements at different settings were compared. It therefore does not establish a randomized comparison between 60 Hz and 130 Hz, nor does it describe either setting as a like-for-like control group. Details about who was masked, how masking was maintained, and whether it was successful are not reported in the registry record.
3. Trial Design
The registry describes a completed study with a single-group model and an enrollment of 20. It lists phase 1 and phase 2. The listed interventions are a procedure changing frequency to 60 Hz and a procedure changing frequency to 130 Hz. The arm description identifies baseline frequency as baseline DBS frequency. These details indicate that the primary comparison is framed around participants’ stride length at baseline and after a frequency change, rather than around separate, randomized groups.
Allocation is recorded as not applicable, and the registry explicitly flags that this is not a randomized comparison and that the arms are not a like-for-like control comparison. The record also lists double masking. It does not describe who was masked, how the masking related to the frequency changes, or whether each participant received both settings. A sequence, washout period, or other ordering procedure is not reported in the registry record and should not be inferred.
The primary outcome is change in stride length from baseline, measured in centimeters. The outcome description specifies evaluation after the DBS frequency setting had been changed for one hour, with comparison to the participant’s baseline DBS frequency stride length. Gait velocity and time to walk 14 meters are listed as secondary outcomes. The registry lists three outcome measures, but does not report their numerical results or the methods used to analyze them.
The study is marked completed, with a start date of 2009-11 and a primary completion date of 2011-08. These registry dates describe the study record; they do not establish when every participant was assessed or how long each participant took part. The protocol, eligibility details beyond the brief description, and the rationale for the enrollment target 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 | Baseline Frequency |
|---|---|
| STARTED | 20 |
| COMPLETED | 19 |
| NOT COMPLETED | 1 |
Reasons for not completing this period:
| Reason | Baseline Frequency |
|---|---|
| Withdrawal by Subject | 1 |
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 | Baseline Frequency |
|---|---|---|
| Participants analysed | 20 | |
| Age, Categorical: <=18 years | Participants | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 13 |
| Age, Categorical: >=65 years | Participants | 7 |
| Age Continuous | years | 62 (SD 5.54) |
| Sex: Female, Male: Female | Participants | 4 |
| Sex: Female, Male: Male | Participants | 16 |
| Region of Enrollment: United States | participants | 20 |
6. Primary Endpoint
The registry lists the primary outcome as Change in Stride Length From Baseline, measured over 1 hour.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Full Range |
| Unit | CM |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is change in stride length from baseline, measured in centimeters. Stride length describes the distance covered by an individual step. The registry’s primary outcome description compares the participant’s stride length at the baseline DBS frequency with stride length after a frequency setting has been changed for one hour. It identifies the parameter as a mean and the dispersion as the full range, but numerical outcome values are not reported in the registry record.
Stride length is used as a measure of gait function. It provides a quantitative way to characterize walking, complementing the secondary outcomes of gait velocity and time to walk 14 meters. A change in a gait measure can describe how an assessment differs between conditions; interpreting the size and precision of that change requires the actual outcome estimates and their variability. Those results are not reported in the registry record, so the direction, magnitude, and precision of the primary endpoint cannot be assessed from the record.
The one-hour timeframe makes the endpoint a short-term assessment following the frequency change. It does not, on its own, describe persistence of any change, effects in everyday activity, or longer-term outcomes. Those questions require data and follow-up information beyond the endpoint description. The registry also does not report a threshold for what would count as a clinically important change in stride length, or how such a threshold would be interpreted alongside the other gait and UPDRS measures.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry supplies a study description and a stated hypothesis, but not numerical efficacy results. In particular, the result for change in stride length from baseline is not reported in the registry record. Numerical results for gait velocity, time to walk 14 meters, and the UPDRS are also not reported in the registry record. It is therefore not possible to describe the observed direction or size of any change, or to assess how precisely an effect was estimated.
The hypothesis that stimulation at 60 Hz would be associated with improved gait and no worsening of UPDRS is an expectation stated in the brief summary. It should not be read as a finding. Without outcome estimates, measures of uncertainty, or reported analyses, the posted record cannot establish whether the observed data supported or contradicted that expectation. It also cannot show whether results at 60 Hz differed from results at 130 Hz.
In general, an estimate describes the effect observed in the analyzed data, while a confidence interval describes the range of values compatible with those data under the analysis assumptions. A narrow interval indicates greater precision than a wide interval; either interval must be interpreted in light of the study design and the outcome being measured. No effect estimate or confidence interval for the primary endpoint is reported in the registry record, so precision cannot be judged.
The single-group model and the registry’s note that this was not a randomized comparison matter for interpretation. A within-participant comparison can help describe how a measurement differs across conditions, but the record does not supply enough procedural detail to determine exactly how such comparisons were made. It does not specify the order of frequency settings, whether every participant experienced both settings, or the analysis used to account for the design. These omissions prevent a detailed assessment of possible order or period effects.
The study is marked completed, but completion status is not an outcome result. The registry lists an enrollment of 20; that figure alone does not establish how many participants contributed to each outcome analysis. The number analyzed, missing measurements, and reasons for missingness are not reported in the registry record. Consequently, the completeness of the outcome data cannot be assessed.
There is no reported analysis in the registry record. Without a stated statistical method, effect estimate, uncertainty interval, or test result, statistical significance and the role of potential confounding cannot be evaluated. The record supports a description of the intended question and measured outcomes, not a conclusion about the direction or reliability of the findings.
9. Statistical Methods Explained
Statistical interpretation begins with matching the analysis to the design and the question. Here, the registry identifies a single-group model and describes stride length after a frequency change relative to baseline frequency. This is not the same design as a randomized comparison in which separate groups are assigned to different settings. The registry itself notes that allocation is not applicable and that the arms are not a like-for-like control comparison. The comparison should therefore be interpreted according to the actual measurement sequence and analysis, details that are not reported in the registry record.
What does a mean describe?
In general, a mean is an average that summarizes a set of measurements. A mean change can express the average within-participant difference between a measurement after a setting change and the baseline measurement, if the analysis is based on paired observations. A mean can be useful for describing the center of a distribution, but it does not show how much individual measurements vary. The registry identifies the primary parameter as a mean, but it does not provide the mean stride-length change or explain the calculation used for the reported outcome.
Why is variability important?
In general, variability describes how spread out observations are. The registry identifies the dispersion for the primary outcome as the full range. A range gives the lowest and highest observed values, but does not by itself show the distribution of values between those points or the precision of an estimated mean. The numerical range is not reported in the registry record. There is also no reported standard error, confidence interval, or other uncertainty measure for the primary endpoint.
For repeated measurements on the same participant, the variability of within-participant differences is often important. Comparing separate summaries of measurements without accounting for pairing can fail to reflect the fact that measurements from one participant are related. The registry does not specify whether the primary analysis used paired data, how repeated measurements were handled, or whether any adjustment was made for the order of frequency settings. These are design and analysis details, not assumptions that can be recovered from the stated outcome description.
What would a confidence interval contribute?
In general, a confidence interval presents uncertainty around an estimated effect. Its width reflects the precision of the estimate under the statistical model and available data. It is not a guarantee that the true effect lies within the interval, and it does not resolve limitations in the design, measurement, or analysis. No confidence interval for stride length or the secondary outcomes is reported in the registry record. As a result, the precision of the estimates cannot be evaluated.
Why does the comparison structure matter?
A randomized comparison can balance, on average, measured and unmeasured characteristics across treatment groups, subject to the conduct of the study. This study is not described as randomized. In a single-group assessment, the interpretation depends on what conditions each participant experienced and how those conditions were ordered. If conditions are measured at different times, changes over time or effects of the order may matter. Those possibilities are general methodological considerations; the registry does not report whether they occurred or how they were addressed.
The registry lists a frequency change to 60 Hz and a frequency change to 130 Hz, and it describes the primary outcome relative to baseline DBS frequency. It does not state that one frequency served as a control for the other, nor does it describe a crossover procedure. It is therefore important not to infer a direct head-to-head estimate or a particular within-participant sequence from the intervention names alone.
How should the planning illustrations be read?
In general, a sample-size planning illustration estimates how many participants per arm might be needed under specified assumptions to detect a chosen effect with a target probability of statistical detection. The registry’s planning description says the illustrations use a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It also states that the effect to detect is a stated fraction of the observed effect. These are planning assumptions, not a description of the study’s original design or proof that the study had a particular probability of detecting an effect.
The record does not report a sample-size justification for the trial’s enrollment of 20. A planning calculation based on an observed effect is conditional on that effect estimate and its assumptions. It does not establish that the estimate is unbiased, precise, or clinically important. Such planning figures are not observed power. The registry’s planning description distinguishes participant counts per arm from total event counts for time-to-event calculations; no time-to-event primary endpoint is identified in this record.
What can be concluded when analyses are absent?
The registry records zero analyses. No statistical model, test, adjustment, estimate, or uncertainty measure is described for the outcomes. General concepts such as statistical significance, model fit, and adjustment for multiple outcomes cannot be applied to this study’s findings without reported analyses. The primary outcome description identifies what was intended to be measured, while the absent results and methods leave the numerical interpretation unresolved.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists a primary outcome of change in stride length from baseline and two secondary outcomes: gait velocity and time to walk 14 meters. The brief summary also states a hypothesis concerning the UPDRS. The record lists three outcome measures and zero analyses, but does not provide numerical findings for these measures or explain whether the UPDRS was analyzed as an outcome.
When a study examines multiple outcomes or makes multiple comparisons, the chance of finding at least one apparently unusual result can increase. In general, a prespecified analysis plan can clarify which outcomes and comparisons are primary and how multiplicity is handled. The registry does not report a multiplicity adjustment, a hierarchy among comparisons, or an analysis plan. It is not possible to determine whether such procedures were used.
Missing-data methods and analysis populations are also not reported in the registry record. The enrollment figure does not identify how many participants had usable data for each endpoint, whether measurements were missing, or how any missing values were handled. The record does not define an intention-to-treat, per-protocol, or other analysis population. Without these details, the potential effect of missing observations on the findings cannot be assessed.
These are reporting gaps, not evidence that a particular method was or was not used outside the registry record. The registry’s zero reported analyses means that statistical findings and their handling of multiplicity and missing data cannot be reconstructed from the record.
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 |
|---|---|---|---|
| Baseline Frequency | 0 | 20 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 5% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Baseline Frequency | 0 of 20 |
The registry’s adverse-event entry is for the baseline-frequency group. It reports 20 participants at risk, zero with serious adverse events, and zero with other adverse events. The number of deaths is not reported in the registry record. No top serious adverse-event terms are listed.
These figures describe the entries in the registry record; they do not establish that no adverse events occurred outside the reported group or reporting period. The record does not provide frequency-specific safety results for the 60 Hz and 130 Hz procedures, nor does it explain the safety surveillance period or methods for collecting events. The baseline-frequency counts should not be treated as a direct comparison of safety between frequency settings.
In general, a zero reported count is not proof that an event is impossible or that a procedure has no risk. Interpretation depends on who was monitored, how events were defined and collected, the duration of observation, and the completeness of reporting. Those details are not reported in the registry record. The registry entry supports only the narrow statement that the listed baseline-frequency group has zero reported serious and other adverse events.
12. What the Result Does, and Does Not, Mean
The registry record describes a study asking whether changing bilateral STN-DBS frequency is associated with short-term differences in gait measures for people with Parkinson disease who had noted a change in walking. Its primary endpoint is change in stride length from baseline after a frequency change has been in place for one hour. The listed settings are 60 Hz and 130 Hz, and the brief summary states a hypothesis involving gait and UPDRS.
The record does not report the numerical results for stride length, gait velocity, time to walk 14 meters, or UPDRS. It therefore does not establish whether any measure increased, decreased, or remained similar, nor how large or precise a change might have been. The stated hypothesis should not be mistaken for an observed result. The registry also does not report statistical analyses that could support a conclusion about statistical uncertainty or comparisons between settings.
Even if a numerical change were available, a short-term change in a measured gait outcome would not by itself establish a durable effect, an effect on daily functioning, or an effect in people outside the described study population. The registry’s one-hour assessment timeframe concerns measurement after the frequency change; longer-term outcomes are not described. The record also does not provide a threshold for clinical importance.
The single-group design and lack of randomized allocation constrain interpretation of any comparison. The registry does not report the sequence of settings, whether all participants experienced both frequency changes, or the approach used to account for repeated measurements. Those details are necessary to understand what a comparison represents. The most defensible conclusion from the registry is therefore about the study’s question and outcome definitions, not about whether a frequency setting produced a particular result.
The safety entry likewise has a narrow scope: it reports zero serious and zero other adverse events for the baseline-frequency group, while deaths are not reported. It does not provide a frequency-specific safety comparison. Neither the efficacy information nor the safety entry in the registry supports a broader claim about benefit or harm.
13. Why This Trial Matters Statistically
This study is statistically informative as an example of why design details matter when interpreting outcomes measured under different conditions. The registry describes one group and a primary comparison with baseline DBS frequency, while listing changes to 60 Hz and 130 Hz. It also explicitly notes that the study was not randomized and that its arms are not a like-for-like control comparison. Readers should therefore distinguish a description of the planned measurement from a randomized estimate of a treatment contrast.
The endpoint focuses on a measurable gait characteristic: stride length. The secondary outcomes extend the assessment to gait velocity and time to walk 14 meters. Considering several related outcomes can provide a broader description, but it also raises questions about which outcomes were prioritized, how comparisons were defined, and whether multiplicity was addressed. These analysis details are not reported in the registry record.
The record also illustrates the difference between a stated hypothesis and reported evidence. The brief summary proposes an expectation about gait at 60 Hz and UPDRS. Without outcome estimates or analyses, that expectation cannot be evaluated. For statistical interpretation, a defined endpoint is only one part of the evidence; results, uncertainty, and a clear account of the analysis are also needed.
Finally, the registry includes an enrollment figure and a limited adverse-event entry, but those details do not fill the gaps in outcome reporting. The number enrolled does not identify the number analyzed for each endpoint, and the baseline-frequency safety counts do not compare the frequency-change procedures. Recognizing what a record does and does not establish is essential to avoid turning a study description into an unsupported conclusion.
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 does not report numerical results for the primary endpoint or the listed secondary outcomes. It also does not report effect estimates, confidence intervals, or statistical tests. This prevents assessment of the direction, magnitude, and precision of the findings.
The design description is limited. The record identifies a single-group model and says the study was not randomized, but it does not describe the sequence of frequency settings, whether participants underwent each setting, or how comparisons were made. The masking status is recorded as double, but who was masked and how masking was implemented are not reported in the registry record. Without these details, the risk of order effects or other influences on repeated measurements cannot be evaluated.
Eligibility criteria beyond the brief description are not reported in the registry record. The number of participants included in each outcome analysis, missing measurements, reasons for missingness, and methods for handling missing data are also not reported. The protocol, statistical analysis plan, and sample-size justification are not reported. The registry identifies planning illustrations, but these do not establish the trial’s original design rationale or observed power.
Safety reporting is limited to the baseline-frequency group, with no frequency-specific comparison described. The observation period and event-collection procedures are not reported, and deaths are not reported in the registry record. These limitations constrain both the efficacy and safety interpretations that can be drawn from the available registry information.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Deep Brain Stimulation (DBS) Frequency Effects on Gait in Parkinson's Disease(PD) — NCT00993291.
- Registry record last updated 2012-01-27; status last verified 2011-12.
- Results first posted 2012-01-27.
- 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.
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18. Record Summary
The registry describes a completed phase 1 and phase 2, single-group study sponsored by Vanderbilt University, with an enrollment of 20. The listed interventions are frequency changes to 60 Hz and 130 Hz. The primary endpoint is change in stride length from baseline, measured in centimeters after a frequency change lasting one hour. Gait velocity and time to walk 14 meters are listed as secondary outcomes.
The record states that allocation was not applicable and flags that the study was not a randomized comparison. It records double masking but does not describe its implementation. The registry lists the study start as 2009-11 and primary completion as 2011-08.
Numerical outcome results and analyses are not reported in the registry record. The safety entry reports zero serious and zero other adverse events for the baseline-frequency group; deaths are not reported. The record describes the study question and measurements, but does not support conclusions about the observed effect or its precision.