Pilot Study of Transcranial Stimulation (tDCS)to Relieve Neuropathic Pain in Cancer Patients: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Pilot Study of Transcranial Stimulation (tDCS)to Relieve Neuropathic Pain in Cancer Patients (NCT01948050), a randomized na study. The primary outcome is Pain Intensity.

2. Clinical Question

The clinical question concerns short-term change in pain intensity after a brief course of stimulation. The endpoint is measured on an 11 point numerical rating scale, with 0 representing no pain and 10 representing the worst pain possible. The registry defines positive change as a decrease in pain intensity and negative change as worsening.

The posted mean changes are 1.66 points for real tDCS and 1.6 points for sham tDCS. These are descriptive arm-level results. The record does not post an estimable two-arm comparison, so the figures do not establish whether the difference between arms is compatible with chance variation or represents a reliable treatment contrast. The registry describes this as a pilot designed to collect preliminary safety and efficacy data, which is distinct from a definitive test of comparative effect.

3. Trial Design

NCT01948050 is a completed, randomized, double-masked, parallel-group pilot study sponsored by Beth Israel Medical Center. The registry lists the phase as NA and enrollment as 24. The study started in 2009-01 and had primary completion in 2012-11. The listed condition is pain.

The registry describes the intended population as cancer patients with neuropathic pain in an affected area after a surgical intervention, radiation therapy, or chemotherapy. The intervention is non-invasive transcranial direct current stimulation (tDCS). Participants in the real-stimulation arm are described as receiving 2mA for 20 minutes at each session on five consecutive days. In the sham arm, the description specifies 30 seconds of stimulation at 2mp and 19 minutes and 30 seconds at 0mp, also on five consecutive days.

Randomization indicates that allocation was intended to use a chance-based process, while the double-masked designation indicates that the registry classifies the study as double-masked. The identities of the people masked, the allocation sequence method, and procedures for maintaining concealment are not reported in the registry record. A parallel design compares separate groups assigned to real or sham stimulation rather than having each participant receive both interventions.

The posted group sizes are 16 for real tDCS and 8 for sham tDCS. Although enrollment and the arm counts are recorded, participant flow, withdrawals, adherence, and the number contributing data at each assessment are not reported in the registry record. The record also does not report a sample-size justification or detailed protocol information. The pilot designation and posted counts describe the study context, but do not by themselves establish whether the design had adequate precision for a definitive comparison.

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: 38 subjects consented; 8 screen failures; 6 never started; 24 were randomized. 1 subject withdrew after undergoing 4 of 5 tDCS/sham sessions. 23 completed randomized study.

Overall Study

Reasons for not completing this period:

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 Pain Intensity, measured over Assessed at baseline and post tDCS stimulation day 5.

The primary outcome is pain intensity, measured in points on an 11 point numerical rating scale. Its anchors are 0 = no pain and 10 = worst pain possible. The registry defines the endpoint as change from baseline to the assessment after tDCS stimulation day 5. Under that definition, a positive change represents decreased pain intensity; a negative change represents worsening pain intensity.

Change from baseline is used to describe how the measured symptom differs after the stimulation period from its starting value. It gives a direct summary of direction and magnitude in the scale's points. In a randomized comparison, the central comparative question is whether the change differs between the assigned arms, not merely whether either arm has a positive mean change. The posted arm means are 1.66 for real stimulation and 1.6 for sham stimulation.

The registry identifies the summary measure as a mean and reports standard errors. A mean summarizes the average change in an arm, while the standard error describes the precision of that estimated mean. It is not a description of the range of individual participant responses. The registry does not post confidence limits for either arm, or an estimable result for the between-arm comparison. Thus the arm summaries describe the endpoint, but do not alone quantify the precision of the treatment contrast.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: it is a score measured in points, and the registry summarizes it using a mean. For each arm, the mean change gives the average baseline-to-post-stimulation day 5 change under the registry's sign convention. Positive values indicate decreased pain intensity, and negative values indicate worsening. The arm means are 1.66 for real tDCS and 1.6 for sham tDCS.

What does a standard error describe?

A standard error describes uncertainty in an estimated quantity, such as an arm mean. It is not the same as the standard deviation of individual participants' scores, and it does not show the full range of experiences. A smaller standard error generally corresponds to a more precisely estimated mean, while a larger one signals greater uncertainty in that estimate. Here the posted standard errors are 0.49 for real tDCS and 0.74 for sham tDCS. Because the arm counts are 16 and 8, respectively, the summaries should be considered alongside those group sizes; they do not reveal the individual-level distribution.

Why is the between-arm comparison central?

In a randomized parallel-group study, the comparative effect is assessed by comparing outcome changes between assigned arms. A positive mean change in an arm is a description of that arm's average change, not proof that the intervention caused the change. The sham arm provides a concurrent comparison, helping account for changes that may occur over the same period for reasons unrelated to active stimulation. The question of interest is whether the changes differ between the arms and how precisely that contrast is estimated.

The registry says the continuous endpoint values are missing or not estimable for a two-arm comparison. It posts no analysis result for this contrast. Therefore, the arm means and their standard errors cannot substitute for a formal comparative estimate, its confidence interval, or a test result. The registry does not report an adjusted analysis or an unadjusted recalculation of the comparison.

What would a confidence interval add?

In general, a confidence interval describes the uncertainty around an estimated effect under a specified statistical method. Its range can show which effect sizes remain reasonably compatible with the observed data and analysis assumptions. For a comparative study, an interval around the between-arm effect is more directly informative about the treatment contrast than separate uncertainty summaries for each arm. No such interval is reported for this endpoint's comparison in the registry record, so the precision of the comparative effect cannot be read from the posted means alone.

Why can small pilot groups limit inference?

General statistical principle: estimates from smaller groups can be imprecise, particularly when participant outcomes vary. An imprecise estimate can be consistent with a range of possible effects, making conclusions about a between-arm difference uncertain. The posted arm sizes are 16 and 8. Those counts and the standard errors describe the amount of outcome information recorded, but they do not establish whether the design was planned to detect a particular difference. The sample-size justification is not reported in the registry record.

What is over-dispersion?

General statistical principle: over-dispersion means observed variability is greater than a statistical model expects. It is especially relevant to count outcomes, where an overly restrictive variability assumption can make uncertainty look too small. This primary outcome is continuous and summarized as a mean with a standard error, so the registry record does not provide a count-model analysis to assess. Individual outcome distributions and modeling details are not reported in the registry record; no conclusion about over-dispersion can be drawn from the arm summaries alone.

How should planning calculations be read?

General statistical principle: sample-size planning calculations illustrate how many participants might be needed under specified assumptions to detect a chosen effect with a chosen error criterion. The registry describes its planning illustration as based on the observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation; the target effect is expressed as a fraction of the observed effect. Such calculations are conditional on the stated assumptions and the estimated effect used. They are not observed power, do not show what the trial actually achieved, and do not establish that the original enrollment target was justified by those assumptions. The original protocol's sample-size rationale and statistical plan are not reported in the registry record.

The distinction between descriptive summaries, comparative estimates, and planning illustrations is essential to interpreting this pilot. The posted means describe observed arm-level change. The registry does not report an estimable contrast or its uncertainty, while any planning illustration answers a hypothetical design question rather than the primary clinical comparison.

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("Real tDCS Stimulation", "Sham tDCS")
n   <- c(16, 8)
m   <- c(1.66, 1.6)
sp  <- c(0.49, 0.74)
sd  <- sp * sqrt(n)      # standard errors converted to SDs
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  Real tDCS Stimulation  16  1.660  1.960  0.616  2.704
CARM  Sham tDCS  8  1.600  2.093  -0.150  3.350

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome measure, pain intensity, and no posted secondary outcome results. A single listed primary measure limits the visible scope of outcome testing, but the statistical plan, prespecified outcome hierarchy, and any multiplicity adjustment are not reported in the registry record. It is not possible to determine from the posted record whether additional outcomes or analyses were planned but not reported.

Missing data and analysis populations affect how outcome summaries should be interpreted. The registry records enrollment of 24 and arm counts of 16 for real stimulation and 8 for sham. It does not report participant flow, reasons for missing assessments, withdrawals, exclusions, adherence, or the number analyzed at each assessment. The analysis population—such as whether participants were analyzed according to their randomized allocation—is not reported in the registry record.

The primary outcome is defined as change from baseline to after stimulation day 5, but the registry does not describe how missing baseline or post-stimulation measurements were handled. It also does not report imputation methods, sensitivity analyses, or adjustments for baseline values. With no estimable two-arm comparison posted, the available summaries cannot resolve how missingness or analysis choices might affect the comparative result.

These omissions do not establish that data were missing or that a particular analysis method was used. They mean that the registry record does not give enough detail to assess those issues. Interpretation should remain limited to the posted arm-level means and standard errors, with no claim about an unreported analysis population or missing-data procedure.

12. Safety Results

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

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: exacerbation of shortness of breath (12.5%), exacerbation of pain due to rectal cellulitis (12.5%), transient change in mental status (12.5%).

The safety summaries list serious adverse events for 1 of 16 participants at risk in the real tDCS group and 1 of 8 participants at risk in the sham group. These counts describe participants with serious adverse events, using the reported at-risk group sizes as denominators. They do not establish that stimulation caused an event, and the registry does not provide a comparative statistical analysis of these counts.

The registry also reports other, non-serious adverse events for 10 of 16 participants in the real-stimulation group and 5 of 8 in the sham group. These are separate from the serious-event counts. The posted summary does not provide a statistical comparison, event-level timing, or information that would establish attribution to the assigned intervention. Death counts are not reported in the registry record.

The listed serious adverse event terms are “Exacerbation of shortness of breath,” “Exacerbation of Pain due to rectal cellulitis,” and “Transient change in mental status,” each reported as 12.5%. The registry lists these terms and percentages but does not provide enough detail to interpret their relationship to treatment or to establish a comparative risk. Safety counts in a pilot study should be read as descriptive observations, not as proof that an intervention is safe or unsafe.

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

The registry record describes a randomized, double-masked pilot comparing real and sham tDCS in cancer patients with neuropathic pain. For the primary outcome, it posts mean changes from baseline to after stimulation day 5 of 1.66 points for real stimulation and 1.6 points for sham stimulation. Both values are positive under the registry's definition of change, so each represents a mean decrease in pain intensity within its arm.

Those figures do not establish a difference between the assigned interventions. The registry states that values are missing or not estimable for a two-arm comparison of this continuous endpoint, and it posts no comparative confidence interval or test result. The arm-level results should not be presented as a statistically established treatment effect, nor do they show whether any change persisted beyond the assessment after day 5.

The posted safety counts document serious and other adverse events in both groups. They are descriptive counts and do not establish whether an event was caused by stimulation or whether the groups differ in risk. No advice about care or treatment follows from these registry summaries.

The study was explicitly described as a pilot intended to collect preliminary safety and efficacy data. Its record can inform readers about the study's design, short-term outcome definition, posted arm summaries, and safety counts. It cannot answer questions that require an unreported comparative estimate, longer-term follow-up, individual participant data, or detailed information on missing observations and analysis populations. The sample-size planning illustrations are conditional calculations, not observed power and not a substitute for an inferential result.

14. Why This Trial Matters Statistically

This study illustrates a key distinction in clinical trial interpretation: within-arm change is not the same as a randomized comparison. The registry reports positive mean changes in both the real and sham groups. Those values describe average change in each arm, but the primary comparative question concerns whether the changes differ between arms. Because the record does not post an estimable two-arm comparison, the distinction directly limits what can be concluded.

The endpoint's sign convention also matters. Positive change is defined as a decrease in pain intensity, while negative change indicates worsening. Clear interpretation depends on applying that convention consistently rather than treating the sign as self-explanatory. The measurement is a numerical rating scale score, so the mean change is expressed in scale points, not as a percentage or a count of participants who improved.

The study also demonstrates why uncertainty measures need context. Standard errors are posted for each arm, but separate standard errors do not supply the uncertainty around the treatment contrast. The unequal posted group counts—16 and 8—are relevant to the precision of the summaries, but do not determine the adequacy of the original design or replace an analysis of the randomized comparison.

Finally, a pilot study can provide useful descriptive information while remaining insufficient for a definitive comparative conclusion. The record identifies a short-term outcome, intervention schedules, arm-level summaries, and safety counts. At the same time, the absence of an estimable comparison and details about analysis populations and missing data shows why transparent reporting of methods and contrasts is important in interpreting clinical trial results.

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 principal limitation for interpreting effectiveness is that the registry does not report an estimable two-arm comparison for the primary continuous outcome. It gives arm means and standard errors, but no comparative estimate, confidence interval, or test result. The numerical similarity of the posted arm means is descriptive and cannot be converted into a conclusion about statistical significance or treatment effect using the registry information.

The outcome is assessed at baseline and after stimulation day 5. The record does not report longer-term follow-up, so durability of change cannot be assessed. It also does not report participant flow, withdrawals, adherence, missing-assessment handling, or analysis populations. These details are important for understanding how closely the posted results represent the randomized groups and how missing observations could affect interpretation.

The registry labels the study a pilot, lists 24 participants enrolled, and posts arm counts of 16 and 8. A sample-size justification, target effect, and detailed statistical analysis plan are not reported in the registry record. Information on allocation concealment, the people masked, and masking procedures is also not reported. The record lists the study as double-masked, but that designation alone does not describe how masking was implemented or assessed.

Safety reporting is also limited to the posted counts and serious-event terms. The registry does not provide a comparative safety analysis or details sufficient to establish event attribution. Secondary outcome results are not posted. These limitations support a cautious, descriptive reading of the record rather than a definitive assessment of effectiveness or safety.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Pilot Study of Transcranial Stimulation (tDCS)to Relieve Neuropathic Pain in Cancer Patients — NCT01948050.
• Registry record last updated 2014-07-14; status last verified 2014-06.
• Results first posted 2014-07-14.
• 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

NCT01948050 is a completed randomized, double-masked, parallel-group pilot sponsored by Beth Israel Medical Center. It enrolled 24 participants and compared real tDCS with sham tDCS in cancer patients with neuropathic pain. The listed phase is NA; the study started in 2009-01 and had primary completion in 2012-11.

The primary outcome was change in pain intensity from baseline to after stimulation day 5, measured on an 11 point numerical rating scale. Mean changes were 1.66 for real stimulation and 1.6 for sham, with standard errors of 0.49 and 0.74, respectively. The registry does not post an estimable two-arm comparison. Serious adverse events were reported for 1 of 16 participants in the real-stimulation group and 1 of 8 in the sham group. The record supports descriptive interpretation but does not provide a comparative statistical result.