Transcranial Direct Current Stimulation for Freezing of Gait: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Transcranial Direct Current Stimulation for Freezing of Gait (NCT02266004), a na na study. The primary outcome is Change in Walking Speed.

2. Clinical Question

The clinical question concerns change during treatment, not a direct comparison between the combined program and a control intervention. The primary measure is walking speed in m/s, recorded using sensors during a 90 second walk. The stated assessment times are baseline and 3 weeks.

The brief summary says the study was intended to evaluate tDCS in combination with locomotor training in patients with Parkinson’s disease and freezing of gait. Since there is no separate control group, a change from baseline would describe the observed course among participants with available measurements. By itself, such a change would not separate intervention effects from other explanations, including natural variation over time or changes associated with participation in locomotor training.

The registry record reports that collected sensor data could not be retrieved for 5 participants who completed the study because of a sensor malfunction. It does not give a primary walking-speed estimate or describe the available participants’ result. Accordingly, the record does not allow the size or precision of the observed change to be assessed.

3. Trial Design

This was an interventional study with a single-group model and no randomization listed. Allocation is recorded as NA, and masking is listed as NONE. The record describes an arm receiving tDCS plus locomotor training; it does not describe a separate control arm. The study is listed as terminated, with enrollment of 9 participants.

The arm description states that tDCS plus locomotor training was given 3x per week for 3 consecutive weeks. The listed primary outcome was change in walking speed, with assessments at baseline and 3 weeks. Other named outcomes include motor scores measured using the Unified Parkinson’s Disease Rating Scale, stride length, postural sway, Timed Up-and-Go time, motor threshold, glutamate/GABA ratio, backward digit span, and Trail Making Test time. The record lists 12 outcome measures overall.

The study began on 2014-09-12, and the primary completion date is 2018-06-27. The reason for termination is not reported in the registry record. The record does not state a phase beyond NA. It also does not report a trial-specific sample-size justification, a prespecified statistical analysis plan, or whether interim analyses were planned.

Because the study has no listed comparison group, the design can describe changes over time within the treated group but cannot directly estimate a difference between treatment strategies. That distinction matters when interpreting any baseline-to-follow-up change: a within-group pattern is not the same as a controlled estimate of what would have happened under another intervention or without the combined program.

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: Unable to retrieve collected data on the other 5 participants who completed the study due to a malfunction in the sensors.

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 Change in Walking Speed, measured over baseline, 3 weeks.

The primary endpoint is change in walking speed, measured in m/s. The registry describes using sensors during a 90 second walk and identifies baseline and 3 weeks as the assessment times. Walking speed is a continuous measure: its mean describes the average observed speed, while its standard deviation describes how spread out individual measurements are around that mean.

Walking speed is used as a direct measure of walking performance. Measuring it at baseline and again after the intervention gives a way to describe whether the group’s recorded walking speed changed over the study period. The measure is distinct from other listed outcomes such as stride length, postural sway, and Timed Up-and-Go time; each captures a different aspect of movement or mobility.

The endpoint description notes that collected data on 5 other participants who completed the study could not be retrieved because of a sensor malfunction. No group mean, standard deviation, change estimate, or uncertainty interval for the primary endpoint is reported in the registry record. Consequently, the statistical size and precision of any walking-speed change cannot be evaluated from the record.

In general, repeated measurement can describe change within participants, but the interpretation depends on the availability and quality of measurements at each time. A change estimate would not, in this single-group design, by itself establish that the intervention caused the change.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The outcome is a continuous measurement, so a mean is a natural way to describe the group’s average walking speed or average change. A standard deviation describes the spread of participant measurements around a mean. These summaries answer different questions: the mean gives a central value, while the standard deviation describes variability among the observed values. The registry identifies the primary parameter as a mean and the dispersion measure as a standard deviation, but does not report the corresponding results.

What does a change estimate represent?

For a repeated-measure outcome, change is based on measurements made at different assessment times. A group mean change would summarize the average within-participant difference for those included in the calculation. It would not convey how much individual participants varied in their changes; that requires information about the distribution of changes or an uncertainty measure. Neither a mean change nor its variability is reported for walking speed in the registry record.

In general, using paired measurements can account for the fact that two observations belong to the same participant. An analysis that treats those measurements as unrelated would not reflect that pairing. The registry does not report the method used to analyze walking-speed measurements, whether paired data were available for all included participants, or how incomplete pairs were handled.

How should uncertainty be read?

In general, a confidence interval gives a range of values compatible with the data under the statistical model used. Its width reflects the precision of an estimate, and its interpretation depends on the analysis assumptions. A point estimate alone does not show how uncertain the result is. The registry record reports no confidence interval for the primary endpoint, so the precision cannot be determined from the record.

A hypothesis test addresses whether the data are sufficiently inconsistent with a specified null hypothesis under its assumptions. A p-value is not the probability that the null hypothesis is true, and it does not measure the size or clinical importance of an effect. No primary-outcome test statistic or p-value is reported in the registry record. The study’s prespecified testing approach is also not reported there.

What do the planning calculations describe?

In general, sample-size planning asks how many participants may be needed to detect a chosen effect with a chosen error rate under stated assumptions. The planning illustrations associated with the posted material are described as using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is stated as a fraction of the observed effect. These calculations are illustrations, not the trial’s reported design justification. They do not represent observed power, and their two-arm allocation assumption does not match the single-group design recorded for this study.

Power is a design quantity tied to assumed effects and variability. It is not a measure of whether an observed finding is valid, and it cannot recover missing endpoint data. The trial’s own sample-size justification and the statistical plan are not reported in the registry record. No sample-size illustration can replace a reported estimate and its uncertainty.

Why can over-dispersion matter?

In general, over-dispersion occurs when outcome variability is greater than a statistical model assumes. When a model understates variability, standard errors may be too small and uncertainty may be understated. The relevance of this issue depends on the outcome and analysis model. The primary endpoint is continuous, and the registry record does not identify a model or report a variability estimate that would allow an assessment of over-dispersion. It would therefore be inappropriate to assert that over-dispersion occurred or that a particular correction was needed.

The main statistical limitation is not a reported conflict between analyses; it is the absence of posted primary outcome estimates and methods. The registry records 0 analyses, and the analysis population, missing-data method, and handling of multiple outcomes are not reported. Without these details and the endpoint results, readers cannot reproduce an estimate, assess assumptions, or gauge its precision.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("tDCS+ LT")
n   <- c(2)
m   <- c(0.169)
sp  <- c(0.244)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  tDCS+ LT  2  0.169  0.244  -2.023  2.361

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 12 outcome measures, including walking speed as the primary outcome and several motor, gait, balance, cognitive, and laboratory measures. When multiple outcomes are examined, the chance of at least one apparently notable result can increase if each is tested separately without an appropriate plan. In general, statistical approaches can address multiplicity, but the choice depends on which outcomes are primary, how tests are organized, and the intended interpretation.

The registry record reports 0 analyses and does not report a multiplicity adjustment, a hierarchy of tests, or a broader statistical analysis plan. It is therefore not possible to determine how the outcomes were intended to be interpreted together. Results for the listed secondary outcomes are not reported in the registry record.

Missingness is directly relevant to the primary outcome: the record says sensor data on 5 participants who completed the study could not be retrieved because of a sensor malfunction. It does not state how many usable primary measurements remained, whether all available measurements were analyzed, or how missing data were handled. The reason for missing data is described, but the record does not establish whether the missing measurements could be related to the outcome values.

The analysis population is not reported in the registry record. It is also not reported whether the analysis included all enrolled participants, only participants with usable sensor data, or another defined group. These omissions prevent assessment of how much the primary result might depend on the handling of unavailable observations.

12. 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 serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: dizziness (11.1%).

The safety record lists 9 participants at risk in the tDCS plus locomotor training group. It records 1 participant affected by a serious adverse event and 1 participant affected by an other adverse event. Deaths are recorded as 0. The registry lists dizziness as the top serious adverse-event term, at 11.1%.

These figures describe events recorded in the registry; they do not, by themselves, show whether an event was caused by the intervention. Serious adverse events and other adverse events are separate reporting categories. The record does not clarify whether the participants counted in those categories were the same or different, so the counts should not be combined or treated as distinct individuals.

The dizziness percentage is reported as 11.1%; it should be read as the registry’s listed percentage rather than as an independently verified rate. Safety findings are also difficult to generalize beyond the study group, given the enrollment of 9 participants and the absence of a comparator group. The registry record does not provide further detail about event timing, severity beyond the serious classification, or causal attribution.

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

The record describes a study intended to evaluate tDCS combined with locomotor training in patients with Parkinson’s disease and freezing of gait. It identifies walking-speed change as the primary outcome and names baseline and 3 weeks as assessment times. It also documents that sensor data on 5 participants who completed the study could not be retrieved because of a malfunction.

What the record does not provide is an estimate of the primary outcome. There is no posted average walking speed, average change, measure of variability, confidence interval, or test result. As a result, the direction and size of a walking-speed change, and how precisely it was estimated, cannot be determined from the registry record.

Even if a within-group change estimate were available, this design would not establish a comparative treatment effect. There is no separate control group described, and tDCS was combined with locomotor training. A change over time could not isolate the contribution of either component or distinguish an intervention-related change from other explanations.

The record’s safety counts document reported adverse-event categories in the study group, including a serious adverse event and an other adverse event, with 0 deaths recorded. Those counts do not establish causation or provide a controlled safety comparison.

Overall, the registry record establishes the intended intervention, design, endpoint, and important data-retrieval limitation. It does not report enough outcome or analysis information to support a conclusion about the size, precision, or cause of changes in walking speed or the other outcomes.

14. Why This Trial Matters Statistically

This study is statistically informative because it illustrates the gap between a clearly named clinical endpoint and an interpretable outcome result. The registry specifies walking speed, its measurement unit, the sensor-based measurement approach, and the assessment times. Yet it does not report the endpoint estimate or its uncertainty, and it documents a sensor malfunction that prevented retrieval of data on 5 participants who completed the study.

The single-group design also makes the target of inference important. A within-group change can describe what happened among participants with available data, but it cannot supply the direct comparison that a control group would support. Since tDCS and locomotor training were delivered together, the design also cannot separate their contributions.

The record lists a range of secondary outcomes and 12 outcome measures overall, while recording 0 analyses. Without posted results and a reported analysis strategy, readers cannot assess whether outcome selection, multiplicity, or missing data influenced interpretation. These are not merely technical details: they determine what an estimate represents and how much confidence can be placed in it.

Finally, planning calculations should be kept distinct from trial results. Illustrative sample-size calculations based on an observed effect are not observed power and do not replace a reported outcome estimate. The study’s own sample-size justification is not reported in the registry record. Together, these features make clear why design details, data completeness, analysis methods, and uncertainty need to be read alongside the clinical endpoint.

15. 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 key trial-specific limitation is incomplete access to the primary sensor data. The registry states that data on 5 participants who completed the study could not be retrieved because of a sensor malfunction, but does not report the resulting analysis population or the amount of usable walking-speed data. The primary outcome estimate and its precision are not reported.

The single-group model and absence of a separate comparator limit causal interpretation. Any available baseline-to-follow-up change would not establish what would have happened under another intervention or without the combined program. Because tDCS and locomotor training were combined, their individual contributions could not be distinguished by this design.

The record lists 12 outcome measures but reports 0 analyses. The analysis plan, missing-data approach, multiplicity handling, and analysis population are not reported in the registry record. The reason for study termination is also not reported. These omissions restrict assessment of how outcomes were selected, how incomplete measurements were treated, and whether the analyses followed a prespecified approach.

The enrollment of 9 participants also means the findings would describe a small study group, even if complete endpoint results were available. The registry’s adverse-event counts are not a controlled comparison, and the record does not report causal attribution. These limitations should be considered separately from the lack of a posted primary outcome estimate.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Transcranial Direct Current Stimulation for Freezing of Gait — NCT02266004.
• Registry record last updated 2020-06-30; status last verified 2020-06.
• Results first posted 2020-06-16.
• 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.

19. Record Summary

NCT02266004 is a terminated, single-group study of tDCS combined with locomotor training in patients with Parkinson’s disease and freezing of gait. The arm description specifies treatment 3x per week for 3 consecutive weeks. Enrollment was 9, masking was listed as NONE, and allocation was recorded as NA.

The primary outcome was change in walking speed, measured with sensors during a 90 second walk at baseline and 3 weeks. The registry notes that collected sensor data on 5 participants who completed the study could not be retrieved because of a malfunction. No primary outcome estimate or analysis is reported in the registry record. The record lists 12 outcome measures and 0 analyses.

The safety record lists 1 serious adverse-event participant, 1 other adverse-event participant, 0 deaths, and dizziness at 11.1% as the top serious term. The reason for termination and the trial’s own statistical analysis and sample-size plans are not reported in the registry record.