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 Effect of Electrical Stimulation (DC Polarization) to the Brain on Memory (NCT00471107), a randomized phase 1, phase 2 study. The primary outcome is Verbal Memory.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00471107 |
| Phase | Phase 1, Phase 2 |
| Condition | Healthy |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Double |
| Enrollment | 45 |
| Arms in the primary outcome | 3 |
| Lead sponsor | National Institute of Neurological Disorders and Stroke (NINDS) |
| Results posted | Yes |
2. Clinical Question
Population
The study enrolled healthy people. The registry description says healthy people 18 years of age and older may be eligible. The recorded enrollment is 45. The primary outcome population is described as all subjects in the relevant group for whom data were obtained.
Intervention
Participants received direct-current brain polarization, also called tDCS in the arm descriptions. The active conditions were left prefrontal anodal and left prefrontal cathodal stimulation, each recorded at 0.08 mA/cm2. The registry description says current could be applied for 25 minutes; the second session involved no stimulation.
Comparator
The comparator was sham TDCS. In the registry description, sham stimulation involved current being turned on only very briefly. Participants were not told which stimulation condition they received. Further details of masking procedures are not reported in the registry record.
Primary question
The primary outcome was the number of words recalled at 24 hours after the words were presented, assessed under anodal, cathodal, and sham conditions. The statistical question is whether the posted mean recall scores differ across these conditions, and how precisely the active-condition results compare with sham. The registry reports an analysis across the three groups; the posted recalculations compare each active arm with sham.
The experimental tasks also included remembering designs, responding to a specified item, and generating words that begin with a particular letter. These tasks give context for the study’s broader interest in learning and memory, but the posted primary outcome is verbal recall. The registry record lists no secondary outcomes.
3. Trial Design
This was a randomized, double-masked, parallel-group study listed as Phase 1 and Phase 2. The registry reports an enrollment of 45 and a completed status. The recorded start was 2007-05, and primary completion was 2010-04. The sponsor was the National Institute of Neurological Disorders and Stroke (NINDS).
The study compared three conditions: left prefrontal anodal TDCS, left prefrontal cathodal TDCS, and sham TDCS. The active-arm descriptions list a current density of 0.08 mA/cm2 for both polarities. The registry description says the first session began with electrodes placed on the participant’s head and arm. Current could be applied for 25 minutes or very briefly as sham stimulation. Participants were not told which type they received. No stimulation was applied in the second session.
Participants attended two experimental sessions at the NIH Clinical Center. The first lasted about 1 hour, and the second, on the next day, took about 10 minutes. The registry describes a list-learning task in which a list of words was read and recalled immediately, with later recall assessed at 24 hours. The primary outcome record defines the result as words recalled under the three stimulation conditions.
The registry lists 12.0 participants in the anodal arm, 14.0 in the cathodal arm, and 12.0 in the sham arm for the primary outcome. The outcome population is described as all subjects in each group for whom data were obtained. The reasons that the recorded outcome counts differ from the enrollment figure, if any, are not reported in the registry record. Details of the randomization method, allocation concealment, masking of study personnel, protocol deviations, and the original sample-size justification 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.
Before assignment: Nothing to report
Overall Study
| Stage | Anodal TDCS | Cathodal TDCS | Sham TDCS |
|---|---|---|---|
| STARTED | 15 | 15 | 15 |
| COMPLETED | 12 | 14 | 12 |
| NOT COMPLETED | 3 | 1 | 3 |
Reasons for not completing this period:
| Reason | Anodal TDCS | Cathodal TDCS | Sham TDCS |
|---|---|---|---|
| Technical problems/data loss | 3 | 1 | 3 |
Analysis population for the primary outcome, as defined in the registry: All subjects in this group for whom data were obtained were analyzed
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 | Anodal TDCS | Cathodal TDCS | Sham TDCS | Total |
|---|---|---|---|---|---|
| Participants analysed | 12 | 14 | 12 | 38 | |
| Age, Continuous | years | 26.5 (SD 8.06) | 32.4 (SD 14.05) | 32.5 (SD 11.29) | 30.57 (SD 11.60) |
| Sex: Female, Male: Female | Participants | 5 | 6 | 8 | 19 |
| Sex: Female, Male: Male | Participants | 7 | 8 | 4 | 19 |
6. Primary Endpoint
The registry lists the primary outcome as Verbal Memory, measured over 24 hours.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Standard Deviation |
| Unit | Words recalled |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is verbal memory measured as the number of words recalled 24 hours after presentation. The registry describes the Wechsler Memory Scale (WMS-III) Word Lists: an examiner reads 12 semantically unrelated words, and the participant immediately recalls as many as possible. The study’s primary outcome is the later verbal recall performance under anodal TDCS, cathodal TDCS, and sham conditions. The registry describes possible scores from 0, meaning no words recalled, to 12, meaning all words recalled.
A word-recall score is a continuous measure in the registry analysis, and the posted group summaries use means and standard deviations. The mean indicates the group’s average number of recalled words; the standard deviation describes the spread of scores among participants in that group. These summaries retain the outcome in its original, interpretable unit: words recalled.
Delayed recall is relevant to the study’s stated question about learning and memory because it assesses remembered material after the initial presentation rather than only immediate performance. The 24-hour timeframe is part of the recorded endpoint definition. The registry describes the endpoint and its measurement but does not report additional validation details, assessment procedures, or rules for handling incomplete word lists beyond the information stated in the record.
7. Results Posted in the Registry
- Left Prefrontal Anodal TDCS: mean 8.62 versus 8.00 on control; difference 0.62 (95% CI -1.26 to 2.51), standardized effect d = 0.27; z-test p = 0.516.
- Left Prefrontal Cathodal TDCS: mean 9.00 versus 8.00 on control; difference 1.00 (95% CI -0.81 to 2.81), standardized effect d = 0.44; z-test p = 0.278.
Mean difference: Left Prefrontal Anodal TDCS
95% CI: -1.26 to 2.51
Recalculated from the posted summary statistics
8. Statistical Interpretation
The posted mean verbal-recall scores were 8.625 words for left prefrontal anodal TDCS, 9.0 for left prefrontal cathodal TDCS, and 8.0 for sham TDCS. The corresponding standard deviations were 1.768, 1.604, and 2.828. These are descriptive summaries for the recorded outcome groups; by themselves, they do not establish whether the observed differences are compatible with chance variation or how precisely the underlying group means are estimated.
The registry reports an ANOVA across the three groups with p >0.05. This reports that the recorded analysis did not meet the conventional threshold reflected by that p-value statement. The registry does not report an ANOVA test statistic, degrees of freedom, group-level confidence intervals, or a more exact p-value. The registry result should be understood as the sponsor’s reported analysis, not as proof that the conditions are identical.
Unadjusted recalculations compare each active condition with sham. The anodal-minus-sham mean difference is 0.625 words, with an interval from -1.262 to 2.512 and an unadjusted p-value of 0.516. The cathodal-minus-sham mean difference is 1.0 word, with an interval from -0.807 to 2.807 and an unadjusted p-value of 0.278. Both estimated differences are positive, but both intervals include zero and extend across values on either side of no difference. This indicates substantial uncertainty about the direction and size of the group contrasts.
The recalculated contrasts are simple, unadjusted comparisons based on the posted summary statistics. They are not the same analysis as the registry’s three-group ANOVA, and they do not account for any adjustment that might have been used in the sponsor’s analysis. The registry record flags a discrepancy between the recalculated results and the sponsor’s reported analysis. The nature of that discrepancy is not reported in the registry record, so the recalculations should not be treated as a replacement for the sponsor’s analysis; the sponsor’s own analysis takes precedence.
The posted results therefore describe average recall scores that are numerically higher in both active arms than in sham, alongside uncertainty that is broad relative to the estimated differences. They do not establish that either active condition differs from sham, nor do they establish equivalence. The registry record does not report a prespecified threshold for a meaningful difference in recalled words, so the practical importance of the observed contrasts cannot be determined from these results alone.
9. Statistical Methods Explained
The primary outcome is a continuous measure: words recalled at 24 hours. A continuous outcome can take a range of numerical values, and the group means offer a compact description of average performance. The standard deviations describe within-group variability, not uncertainty in the group mean. A larger standard deviation means observations are more spread out around that group’s mean. Here, the posted standard deviations are 1.768 for anodal TDCS, 1.604 for cathodal TDCS, and 2.828 for sham.
What does the registry’s ANOVA assess?
ANOVA, or analysis of variance, is a general method for assessing whether the means across multiple groups are consistent with a common mean. In this study, the recorded analysis includes the anodal, cathodal, and sham groups. The registry reports p >0.05. In general, a p-value describes how surprising data at least as incompatible with the tested null model would be if that model were true. It does not give the probability that the null model is true, and it does not measure the size or importance of a difference. The registry record does not give a more detailed ANOVA result, such as a test statistic or exact p-value.
What do the recalculated contrasts represent?
The posted recalculations express each active-arm mean relative to the sham mean. For anodal TDCS, the estimated mean difference is 0.625 words, with an interval from -1.262 to 2.512 and unadjusted p = 0.516. For cathodal TDCS, the estimated mean difference is 1.0 word, with an interval from -0.807 to 2.807 and unadjusted p = 0.278. A positive contrast means the active-arm mean is higher than the sham mean in the posted summaries. The intervals also include zero, so the results are compatible with no difference as well as with differences in either direction over the ranges stated.
These are unadjusted comparisons: they do not account for multiple testing or other adjustments. They are also recalculations from posted summary statistics rather than the sponsor’s reported analysis. Because the registry record indicates a discrepancy, the sponsor’s own analysis takes precedence. The record does not explain the source or nature of the discrepancy. The two approaches should therefore be read as distinct statistical descriptions, not combined into a single definitive test.
How should standard errors and pooled spread be understood?
A standard error describes the estimated uncertainty in a sample mean, given the observed spread and sample size. The recalculation records standard errors for the sham and active-arm means; for the sham mean, the listed standard error is 0.816 in both comparisons. The active-arm standard errors are 0.510 for anodal TDCS and 0.429 for cathodal TDCS. Standard errors are not the same as standard deviations: the latter describe participant-to-participant variation, while the former describe precision of a mean estimate.
The recalculations also list pooled standard deviations of 2.358 for the anodal comparison and 2.249 for the cathodal comparison. In general, pooling combines information about variability across the two groups being compared, under the assumptions of the calculation. The standardized effects listed are 0.265 and 0.445, respectively. A standardized effect expresses a mean contrast relative to a pooled measure of spread, rather than in words recalled. These values are derived summaries and do not replace the original-unit contrasts, which are easier to interpret clinically and educationally.
What can and cannot be inferred from the analysis?
In general, a statistical test and an interval answer related but different questions. The p-value summarizes compatibility with a null model under specified assumptions; an interval conveys a range of estimates compatible with the data and method. Neither alone establishes that an effect is important. A non-significant result does not show equivalence, and a positive point estimate does not establish a reliable difference. Equivalence or non-inferiority claims require a defined margin and an analysis designed for that question; such a margin is not reported in the registry record.
The registered outcome population is described as all subjects in each group for whom data were obtained. The registry does not explain how missing outcome data were handled, or whether the analysis followed an intention-to-treat principle. The randomization method, model details, assumptions checks, and any covariate adjustment are not reported in the registry record. These omissions limit how fully the reported analysis can be independently interpreted from the registry information.
10. Confidence Intervals and Precision
The recalculated mean differences are accompanied by intervals that communicate uncertainty around each contrast. The anodal-minus-sham estimate is 0.625 words, with an interval from -1.262 to 2.512. The cathodal-minus-sham estimate is 1.0 word, with an interval from -0.807 to 2.807. The registry does not identify the confidence level for these recalculated intervals, so no confidence percentage is assigned to them.
Both intervals include zero. In general, when an interval for a difference includes zero, the data and method do not rule out no difference at the interval’s stated range. The intervals also include positive and negative values, so the posted data leave uncertainty about whether the active-arm mean is higher or lower than the sham mean in the wider population. Their breadth relative to the point estimates means that the estimates are not very precise.
A confidence interval is a general statistical tool: under repeated use of the same method and its assumptions, intervals constructed in that way would cover the target quantity at the method’s stated rate. It is not a probability statement about the fixed true effect after a particular interval has been calculated. The registry reports a 95% level for the ANOVA record, but that analysis has no estimate or interval values posted. The recalculated pairwise intervals and the registry’s ANOVA should not be conflated.
Precision is affected by the amount of information in the data and by outcome variability. The recorded outcome groups contain 12.0 participants for anodal TDCS, 14.0 for cathodal TDCS, and 12.0 for sham, with observed standard deviations from 1.604 to 2.828. These group sizes and spreads help explain why the recalculated comparisons remain uncertain, but the registry record does not provide a prespecified precision target or a threshold for an important difference.
11. Planning a Similar Trial: Sample Size
This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.
| Effect to detect | Participants per arm, 80% power | Participants per arm, 90% power |
|---|---|---|
| 100% of the observed effect | 224 | 300 |
| 75% of the observed effect | 398 | 532 |
| 50% of the observed effect | 895 | 1,197 |
The planning figures are participants per arm for 80% power and participants per arm for 90% power. They are not total events: the outcome is continuous, and the values refer to the number of participants in each of two comparison arms. For the anodal-versus-sham comparison, planning for 100% of the observed effect gives 224 participants per arm for 80% power and 300 for 90% power. Planning for 75% of the observed effect gives 398 and 532 participants per arm, respectively; planning for 50% gives 895 and 1,197. For the cathodal-versus-sham comparison, the corresponding figures are 80 and 107 for 100% of the observed effect, 142 and 190 for 75%, and 318 and 426 for 50%.
The planning calculation assumes a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each row uses the stated fraction of the observed effect as the effect to detect. The 80% power column represents the planned sample size at which the calculation targets an 80% chance of detecting the specified effect under those assumptions if that effect is present. The 90% column uses a higher target chance of detection, and therefore requires more participants for each listed comparison.
Smaller effects require more participants because they are harder to distinguish from random variation. These are planning illustrations based on the observed effects, not the trial’s original design justification; the original sample-size assumptions are not reported in the registry record. They are not observed power.
12. How the Sample Size Is Derived
Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z1−α/2 = 1.960) and the desired power (z1−β = 0.842 for 80% and 1.282 for 90%).
Formula
n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.
Worked calculation for this trial
- Observed difference Δ = 0.625; pooled standard deviation σ = 2.358.
- n = 2 × (1.96 + 0.842)2 × 2.3582 / 0.6252 = 223.5, rounded up to 224 participants per arm for 80% power.
The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).
R code
alpha <- 0.05
z_a <- qnorm(1 - alpha / 2) # two-sided
delta <- 0.625 # observed difference in means
sigma <- 2.35832652531408 # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))
# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")
# Simulation: exact two-sample t-test using simulated means and variances
set.seed(471107)
n <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n)) # difference in sample means
s2 <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1)) # pooled sample variance
tstat <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))
Output from running the code
100% of observed effect: n per arm = 224 (80% power), 300 (90% power)
75% of observed effect: n per arm = 398 (80% power), 532 (90% power)
50% of observed effect: n per arm = 895 (80% power), 1,197 (90% power)
power.t.test: 224.5
Simulated power at n = 224 per arm: 0.798 (20000 replicates)The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.
13. Analyses Reported by the Sponsor
| Method | Estimate | 95% CI | P-value |
|---|---|---|---|
| ANOVA | not reported | > 0.050 |
The registry reports the sponsor’s own analysis as an ANOVA across the three groups, with p >0.05 and a 95% confidence level recorded for the analysis. No ANOVA estimate, confidence interval, test statistic, or exact p-value is reported. The unadjusted recalculations instead compare each active arm separately with sham using the posted group means and standard deviations. They give an anodal mean difference of 0.625 with unadjusted p = 0.516, and a cathodal mean difference of 1.0 with unadjusted p = 0.278.
The registry flags a discrepancy between the recalculated results and the sponsor’s reported analysis. The nature of the discrepancy is not reported in the registry record, so it is not possible to identify its source or reconcile the two analyses from the record alone. The recalculated contrasts are unadjusted and are not a substitute for the sponsor’s three-group ANOVA. The sponsor’s own analysis takes precedence. Both should be described accurately: the sponsor reported p >0.05 for the ANOVA, while the separate unadjusted recalculations show the estimates and intervals stated above.
14. Multiplicity, Missing Data and Analysis Populations
The registry lists one primary outcome measure and no posted secondary outcomes. It reports an ANOVA covering the three study groups. The recalculated comparisons separately examine anodal TDCS versus sham and cathodal TDCS versus sham. No multiplicity-adjustment procedure for these pairwise comparisons is reported in the registry record, and the recalculated p-values are explicitly unadjusted. When multiple hypotheses are tested, the chance of at least one chance finding can increase; adjustment methods can address that issue, but the choice of method depends on the analysis plan. No such plan is reported.
The registry describes the primary outcome population as all subjects in the relevant group for whom data were obtained. This describes who was analyzed in general terms, but it does not state how many randomized participants lacked outcome data or why. The registry record does not report a missing-data method, imputation procedure, sensitivity analysis, or detailed participant flow for the primary outcome. It also does not report whether participants were analyzed according to their randomized assignment, regardless of treatment received.
The distinctions matter because missing outcomes can affect estimates if the probability of being observed is related to the outcome or treatment condition. In general, an analysis based only on participants with observed outcomes can differ from one that accounts for missingness, depending on the reasons for and pattern of missing data. Without further information, the effect of missing data on the posted results cannot be assessed.
The registry record does not report the original statistical analysis plan, prespecified contrasts, covariate adjustments, interim analyses, stopping rules, or the trial’s sample-size justification. These are not assumed to have been absent from the conduct of the study; their status is simply not reported in the registry record. The lack of those details limits assessment of whether the posted analyses align with the original plan.
15. 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 |
|---|---|---|---|
| Anodal TDCS | 1 | 12 | 8.3% |
| Cathodal TDCS | 0 | 14 | 0.0% |
| Sham TDCS | 0 | 12 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 2% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Anodal TDCS | 0 of 12 |
| Cathodal TDCS | 0 of 14 |
| Sham TDCS | 0 of 12 |
Most frequent serious adverse event terms
| Event term | Organ system | Anodal TDCS | Cathodal TDCS | Sham TDCS |
|---|---|---|---|---|
| Burn | Skin and subcutaneous tissue disorders | 1 of 12 | 0 of 14 | 0 of 12 |
Serious events with the highest arm-level rate: burn (8.3%).
The serious adverse event figures list 12 participants at risk in the anodal group, 14 in the cathodal group, and 12 in the sham group. Serious adverse events affected 1 participant in the anodal group, 0 in the cathodal group, and 0 in the sham group. The listed serious-event term is Burn, with 8.3% recorded. The record does not provide further detail about the event’s timing, severity, relationship to stimulation, or outcome.
The separate other-adverse-event counts show 0 affected participants in each of the three groups. Death counts are not reported in the registry record; blank death fields should not be read as a reported zero. The serious-event percentages and counts are descriptive registry entries. They do not establish whether an event was caused by the intervention, and they should be interpreted in light of the small recorded groups and the limited detail available in the registry.
These figures concern the participants included in the safety reporting and should not be confused with the primary verbal-memory outcome. The registry record does not provide a broader safety analysis, detailed event narratives, or information about how adverse events were collected.
16. What the Result Does, and Does Not, Mean
The posted results describe mean 24-hour recall scores of 8.625 words for anodal TDCS, 9.0 for cathodal TDCS, and 8.0 for sham. In the unadjusted recalculations, the active-arm estimates are higher than the sham mean by 0.625 and 1.0 words. The intervals for both contrasts include zero and extend across positive and negative values. The sponsor’s reported ANOVA has p >0.05.
Taken together, these records show that the observed group means were not identical, while the statistical analyses leave substantial uncertainty about the size and direction of population differences. The results do not establish that either active condition differs from sham. They also do not show that the conditions are equivalent. A failure to meet a statistical significance threshold is not evidence that two conditions have the same effect; an equivalence conclusion requires a prespecified margin and suitable analysis, neither of which is reported in the registry record.
The study’s endpoint is a specific verbal-recall measure at a particular follow-up time. It does not, by itself, represent every aspect of memory, learning, everyday functioning, or longer-term outcomes. The registry also describes other experimental tasks, but it does not post secondary outcomes for them. The posted primary results therefore should not be generalized beyond the measure and conditions recorded.
The registry record describes healthy participants and a controlled experimental setting. It does not support conclusions about people with memory disorders or other clinical populations. Nor does it provide enough information to determine the practical importance of a difference of the estimated size: no threshold for a meaningful change in recalled words is reported. These findings are statistical descriptions of the recorded study results, not medical advice or a recommendation about treatment.
17. Why This Trial Matters Statistically
This study illustrates the difference between a point estimate and the strength of evidence around it. The active-arm means are numerically higher than the sham mean, but the unadjusted intervals include zero and allow a range of possible contrasts. Looking only at the ordering of the means would miss the uncertainty; looking only at the reported p-value would omit the estimated size and the outcome’s natural unit.
It also illustrates why analysis descriptions matter. The sponsor reports a three-group ANOVA, while the posted recalculations provide two active-versus-sham contrasts. Those analyses answer related but not identical questions. The registry flags a discrepancy but does not explain it, so careful interpretation requires keeping the sponsor’s result distinct from the recalculated comparisons and giving precedence to the sponsor’s own analysis.
The outcome is expressed in words recalled, which gives a direct interpretation of the estimated differences. Standard deviations and intervals add information about variability and precision, while the planning illustrations show how sample-size requirements depend on the effect size assumed for detection. Those planning values should not be confused with the study’s actual enrollment or with evidence that a target level of power was achieved.
Finally, the registry’s incomplete reporting of missing-data handling, multiplicity procedures, and the original design assumptions demonstrates the importance of transparent statistical plans. Such details help readers evaluate whether the analysis was prespecified, how uncertainty was handled, and how broadly the results can be interpreted. Their absence from the registry record limits that evaluation without, by itself, demonstrating how the study was conducted.
18. 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 available registry information supports only a limited assessment of design and analysis. Although the study is identified as randomized, double-masked, and parallel-group, the randomization sequence, allocation concealment, masking procedures, and assessment of masking are not reported in the registry record. The exact stimulation schedule and implementation details beyond the description of current duration and conditions are also limited.
The primary outcome group counts are 12.0 for anodal TDCS, 14.0 for cathodal TDCS, and 12.0 for sham, while the registry enrollment is 45. The reason for the difference between recorded enrollment and outcome-group counts is not reported in the registry record. Participant flow, exclusions, protocol deviations, and the number or reasons for missing primary outcome measurements are not described in the posted record.
The sponsor’s ANOVA is reported only as p >0.05, without a test statistic, exact p-value, or group-level uncertainty estimates. The recalculated pairwise contrasts are unadjusted, and the registry flags a discrepancy without explaining it. The confidence level for the recalculated intervals is not specified in the comparison details. The original analysis plan, multiplicity handling, model assumptions, sample-size rationale, interim analyses, and stopping rules are not reported in the registry record.
The endpoint is a particular verbal-memory score measured at 24 hours. No secondary outcomes are posted, and the registry does not state a threshold for a meaningful difference. The adverse-event record gives limited event detail and does not report death counts. These constraints mean the posted results are best read as a narrow statistical account of the recorded primary outcome, rather than a complete evaluation of all study procedures or outcomes.
19. Related Tutorials
20. Related Statistical Calculators
21. Sources
- ClinicalTrials.gov: Effect of Electrical Stimulation (DC Polarization) to the Brain on Memory — NCT00471107.
- Registry record last updated 2016-03-24; status last verified 2013-03.
- Results first posted 2013-05-15.
- 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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22. Record Summary
The registry describes a completed randomized, double-masked, parallel-group Phase 1 and Phase 2 study of direct-current brain polarization in healthy participants, with recorded enrollment of 45. The primary outcome was the number of words recalled 24 hours after presentation under anodal, cathodal, and sham conditions.
Mean scores were 8.625 words for anodal TDCS, 9.0 for cathodal TDCS, and 8.0 for sham. The sponsor reported an ANOVA with p >0.05. Unadjusted recalculations give mean differences of 0.625 words for anodal versus sham and 1.0 word for cathodal versus sham; both intervals include zero. The registry flags a discrepancy, and the sponsor’s own analysis takes precedence.
The registry does not report the original sample-size justification, detailed missing-data handling, or a multiplicity procedure. Serious adverse events affected 1 anodal participant and none in the other listed groups; further event details are limited in the record.