Investigating Transcranial Direct Current Stimulation (tDCS) in Accelerating Learning in a Healthy Older Population: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Investigating Transcranial Direct Current Stimulation (tDCS) in Accelerating Learning in a Healthy Older Population (NCT03467698), a randomized na study. The primary outcome is A Computerized Verbal Paired-associate Memory Task Will be Used to Assess Memory Performance..

2. Clinical Question

The stated study objective is to explore whether tDCS can accelerate associative learning and boost associative memory in healthy subjects. The endpoint description gives a specific task and two assessment occasions, but does not provide a posted result for either occasion or a reported estimate of the between-group difference. Thus the clinical question can be described from the design and intended measurement, but the registry entries in this record do not establish what the observed memory scores were.

3. Trial Design

The registry describes a randomized, double-masked, parallel-group study with active tDCS and sham tDCS arms. Randomization indicates that assignment was intended to be determined by a chance-based process, while double masking indicates that the record characterizes the study as masked for two parties. The identities of the masked parties, the randomization procedure, and the safeguards used to maintain masking are not reported in the registry record. The parallel model indicates separate groups receiving the active or sham condition rather than a crossover design as described in the record.

The recorded enrollment is 30. The adverse-event information lists 15 participants at risk in each arm; those arm-specific entries do not, by themselves, describe the outcome-analysis population or establish who completed each assessment. The registry status is completed. The recorded start date is 2018-02-21 and the primary completion date is 2022-09-17. These dates describe the registry record and do not supply details about recruitment pace, follow-up completion, or protocol changes.

The study lists one primary outcome measure: performance on a computerized verbal paired-associate memory task, expressed as the percentage of words learned or remembered. Its stated timing includes baseline assessment at visit 1 and a memory assessment at visit 2 one week later. The outcome description says memory performance scores from each visit will be compared between the active and sham groups. It does not specify the exact statistical model, the particular contrast used to represent change, or whether a baseline-adjusted analysis was planned.

The registry lists the study phase as not applicable. It identifies The University of Texas at Dallas as the sponsor. The population and intervention descriptions are brief, and further operational details about eligibility, dose, treatment schedule, allocation concealment, protocol deviations, and participant flow are not reported in the registry record. Consequently, the design can be characterized at a high level, but important details needed to reproduce the study or assess implementation cannot be established from this record alone.

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

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 A Computerized Verbal Paired-associate Memory Task Will be Used to Assess Memory Performance., measured over Memory performance changes will be assessed in two different visits. First assessment (baseline) on visit 1 (learning), then one-week after during visit 2 (memory).

The primary endpoint is memory performance on a computerized verbal paired-associate task. The registry describes the measure as the percentage of words learned or remembered. A paired-associate task assesses whether a participant can learn and later recall linked verbal items; the percentage scale expresses performance as a proportion of the words relevant to the task. The registry does not report the task’s item count, scoring rules, alternate forms, or criteria for a valid assessment, so those details cannot be inferred.

Assessment is described at two occasions: baseline on visit 1, characterized as learning, and a memory assessment at visit 2 one week later. This arrangement is intended to capture learning performance and subsequent memory performance, rather than relying only on a single assessment. Measuring performance at both occasions can be useful when the research question concerns learning and later retention. However, the registry does not state precisely how the two measurements were combined or which visit-specific result defines the primary comparison.

The endpoint is reported as a mean with standard error as the stated dispersion. A mean gives a group-level summary of observed scores; a standard error describes the precision of an estimated mean under the analysis assumptions, rather than the spread of individual participants’ scores. No endpoint values, standard errors, group contrast, or confidence interval are reported in the registry record. The measure therefore clarifies what the investigators intended to assess, but does not reveal the observed performance or its precision.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a randomized, double-masked, parallel-group design and a continuous primary outcome summarized as a mean with standard error. These labels convey the broad methodological framework, but the record does not report a statistical analysis plan or any analysis results. The explanations below are general descriptions of the methods concepts named in the record, not claims about procedures that were used but not documented.

What does randomization contribute?

In general, random assignment is intended to make treatment groups comparable with respect to both measured and unmeasured characteristics, on average across repeated assignments. It does not guarantee that groups will be identical in a particular trial, especially when the study is limited in size. Randomization can support a causal interpretation of a between-group comparison when allocation is implemented as planned and outcome data are handled appropriately. The registry identifies allocation as randomized, but the sequence-generation method, concealment procedures, and any stratification are not reported in the registry record.

What does masking mean?

The record labels the study double-masked. In general, masking can reduce the influence of expectations on participant behavior, study conduct, outcome assessment, and interpretation. The label alone does not identify which parties were masked or whether masking remained effective. For a device-based intervention with a sham comparator, the sham procedure is relevant to how participants may perceive assignment, but the precise sham method and an assessment of masking are not reported in the registry record. It would therefore be inappropriate to assume that masking was successful solely from the design label.

How should a mean and standard error be understood?

For a continuous outcome, a mean represents the average score in a group under the stated scoring approach. The standard error describes uncertainty in the estimated mean, rather than the variability of individual scores. A standard deviation, by contrast, describes how spread out individual observations are around the mean. The registry names standard error as the dispersion but posts no numerical mean or standard error for the outcome. Without those values, readers cannot assess the observed group-level performance or precision.

Why does the analysis definition matter?

The outcome is assessed at baseline on visit 1 and one week later on visit 2. A comparison might focus on the later scores, changes from baseline, or a model that adjusts later scores for baseline. These approaches answer related but not identical questions and rely on different assumptions. Repeated measurements may also be modeled jointly. The record says scores from each visit will be compared between groups, but the precise estimand, model, covariates, handling of repeated observations, and planned contrasts are not reported in the registry record. No one approach should be attributed to the study without documentation.

What would a confidence interval add?

In general, a confidence interval displays the uncertainty around an estimated contrast under a specified statistical model. It conveys both the direction and the range of effect sizes reasonably compatible with the data and assumptions. A narrow interval indicates greater precision than a wide interval, but precision alone does not establish clinical importance. A significance test answers a different, narrower question about compatibility with a null hypothesis under model assumptions. The registry record does not report a contrast, confidence interval, or test result, so these features cannot be interpreted for this trial.

How do planning illustrations differ from results?

The record describes a planning illustration based on the observed effect, using a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation. It says the effect to detect is a stated fraction of the observed effect, and specifies that non-time-to-event planning outputs are participants per arm. No planning output values or observed effect estimate are reported in the registry record. A sample-size illustration is a hypothetical planning calculation under stated assumptions; it is not an observed trial outcome and is not observed power. In general, using an effect estimated from a study as a planning input can make the illustration dependent on that estimate and its uncertainty. The record does not report the effect estimate or the resulting planning values, so no numerical planning conclusion can be drawn.

What role does over-dispersion have?

Over-dispersion is a general concern when observed variability exceeds what a statistical model assumes. If it is ignored, estimated standard errors can be too small, making uncertainty appear lower than it is. The primary outcome is described as a percentage of words learned or remembered, but the record does not provide its score distribution, denominator, model, or an assessment of over-dispersion. It is therefore not possible to say whether over-dispersion was present or whether an adjustment was used. This is a general consideration for analyzing bounded or count-derived outcomes, not a finding about this trial.

In short, the available methods descriptions identify the broad design and endpoint but leave key analytic decisions undocumented. The registry record does not report a detailed statistical plan, analysis population, missing-data approach, multiplicity procedure, or outcome estimates. General statistical concepts can clarify what such details would mean, but cannot fill in the trial-specific methods or results that are not reported.

10. Multiplicity, Missing Data and Analysis Populations

The registry identifies one primary outcome measure, with assessment at baseline during visit 1 and at visit 2 one week later. Having one named outcome measure does not resolve how multiple assessment occasions or possible contrasts were handled. The record does not report a multiplicity strategy, a hierarchy among visit-specific tests, or whether any adjustment for multiple comparisons was planned. Multiplicity methods address the increased chance of false-positive findings when several statistical claims are evaluated. This is a general concern; the record does not establish that such adjustments were needed or used.

Missing-data handling is also not reported in the registry record. The endpoint description does not state how incomplete task responses, missed visits, withdrawal, or unusable assessments were treated. It does not give the number of participants with endpoint data at either visit, or explain whether all randomized participants were included in an analysis. The adverse-event risk counts should not be taken as outcome-analysis denominators: they describe the adverse-event entries, not the availability of memory scores.

The analysis population is not reported in the registry record. In general, an intention-to-treat approach analyzes participants according to their randomized assignment, whereas other analysis populations may require treatment receipt or outcome availability. Different populations can lead to different interpretations and may be affected by post-randomization exclusions. No such population definition or accounting is given for this study.

The registry describes a comparison between the active and sham groups, but the model, covariate adjustment, treatment of repeated measurements, and prespecified contrast are not reported. A distinction between a prespecified analysis and analyses selected after seeing results can be important when judging inferential strength. The record does not provide enough information to determine which analyses, if any, were prespecified. These absences limit interpretation of the statistical evidence; they do not prove that the study team lacked plans or performed no analyses.

11. 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 1% reporting threshold.

The registry’s adverse-event entries report zero serious adverse events in the active tDCS group and zero in the sham tDCS group. The listed number at risk for serious adverse events is 15 in each group. The entries also report zero other adverse events in each group, with 15 at risk for those events in each group. No serious adverse-event terms are listed.

These figures are counts recorded in the registry, not a complete safety analysis. Zero recorded events means that no events are reported in these fields; it does not establish that the intervention cannot cause adverse events or that none occurred outside the scope or period of collection. The record does not define the serious or other adverse-event categories, specify the observation window, describe active versus passive surveillance, or report how events were assessed and attributed.

The risk entries do not tell readers whether every participant completed safety follow-up, whether event reporting was complete, or whether event severity and timing were evaluated. Nor do they provide outcome data about memory performance. The appropriate reading is limited: the registry reports no serious or other adverse events in the listed entries, while further detail about ascertainment and follow-up is not reported in the registry record.

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

The record establishes a study question: whether active tDCS, compared with sham tDCS, is associated with differences in performance on a computerized verbal paired-associate memory task in healthy subjects. It also describes a randomized, double-masked, parallel-group design and assessments at baseline and one week later. These details explain the intended comparison and measurement, not its result.

No primary outcome values or analysis results are reported in the registry record. Consequently, the record does not show whether the active and sham groups differed, whether scores changed between visits, or how precisely any contrast was estimated. It cannot support a claim that tDCS improved memory, that it failed to do so, or that the groups were equivalent. An absence of posted results is not evidence of a zero effect.

Even when outcome data are available, statistical significance and practical importance are distinct questions. A small estimated difference can be statistically detectable but not meaningful to a research or clinical question; an uncertain estimate can also be compatible with a range of effects. Those judgments require the estimated effect, its uncertainty, and a rationale for what constitutes a meaningful difference. Such information is not reported in the registry record, so neither statistical nor practical importance can be assessed.

The recorded enrollment and design labels do not replace results. A completed study is not necessarily a study with posted outcome analyses, and the presence of an endpoint definition does not establish what was observed. Likewise, the reported zero adverse-event counts are limited registry entries and do not answer the primary memory question or provide a comprehensive safety assessment.

The most defensible conclusion is therefore about the limits of the record: it documents the intended design, intervention comparison, and endpoint, but does not report the primary outcome results or statistical analyses. Readers should distinguish this lack of reported evidence from evidence that there was no difference or no effect.

13. Why This Trial Matters Statistically

This trial is statistically interesting because its stated objective connects a device intervention with learning and later memory, while the primary endpoint uses a behavioral task measured at more than one occasion. Such a design raises useful questions about how a study defines learning, retention, and the contrast that answers its research question. The registry gives the task, unit, and timing, but not the detailed estimand or analysis needed to resolve those questions.

The randomized, double-masked, parallel-group framework also illustrates why design labels are only a starting point for statistical interpretation. Randomization can support group comparability, while masking can limit some sources of bias. Their practical value depends on implementation, which the registry does not describe in detail. The intervention and sham procedures are named, but stimulation parameters, allocation procedures, and checks on masking are not reported in the registry record.

A further statistical lesson is the difference between an outcome plan and an outcome result. The registry identifies a mean-based continuous endpoint, but does not report group summaries, a contrast, or uncertainty. Without those elements, readers cannot judge magnitude, precision, or compatibility with different effect sizes. The listed completion status and sample enrollment do not fill that evidential gap.

The planning assumptions also highlight that design calculations and observed findings serve different purposes. A planning illustration based on an observed effect can help frame hypothetical future-study scenarios, but it does not provide a result for the present trial and is not observed power. In this record, the assumptions are described but numerical illustration outputs are not reported.

For clinical researchers and biostatisticians, the key value of this record is therefore methodological transparency about the intended question, alongside clear limits on what can be inferred. It shows why endpoint specification, analysis definitions, outcome reporting, missing-data accounting, and uncertainty estimates are all essential to a useful trial interpretation.

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 principal limitation for interpreting this trial from the registry record is the absence of posted primary outcome values and analyses. Without group summaries, a between-group estimate, and a measure of uncertainty, readers cannot evaluate the magnitude, direction, or precision of the memory comparison. The registry’s completed status does not address this limitation.

The endpoint definition leaves several measurement details unspecified. The record does not describe the task’s item structure, scoring rules, validity criteria, or how incomplete responses were handled. Although it names baseline assessment at visit 1 and a memory assessment at visit 2 one week later, it does not clarify how learning and memory performance were combined or which contrast was primary.

Important design and analysis details are also not reported in the registry record. These include eligibility criteria, stimulation settings and schedule, allocation concealment, the parties masked, assessment of masking, protocol deviations, the analysis population, model specification, handling of repeated measurements, and any prespecified covariates. Missing-data methods and multiplicity procedures are likewise not reported. Their absence from the record makes it harder to judge risk of bias and reproduce the analysis, but does not demonstrate that the procedures were absent from the study.

The safety entries are limited to the recorded event counts and risk groups. Definitions, surveillance methods, follow-up duration, and event attribution are not reported. The entries therefore should not be treated as a comprehensive account of safety.

Finally, the planning description does not include numerical outputs or the observed effect used as its input. It cannot be used to infer the trial’s achieved precision or the design’s adequacy. Taken together, these limitations mean the record is informative about the intended study question but insufficient for a full assessment of its findings or methods.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Investigating Transcranial Direct Current Stimulation (tDCS) in Accelerating Learning in a Healthy Older Population — NCT03467698.
• Registry record last updated 2024-01-09; status last verified 2023-12.
• Results first posted 2024-01-09.
• 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.

18. Record Summary

The registry record identifies NCT03467698 as a completed, randomized, double-masked, parallel-group study sponsored by The University of Texas at Dallas. It compares active HD-tDCS with sham HD-tDCS in a study described as involving associative memory in healthy subjects and a healthy older population.

The primary outcome is performance on a computerized verbal paired-associate memory task, measured as the percentage of words learned or remembered. Assessments are described at baseline on visit 1 and at visit 2 one week later. The recorded enrollment is 30, and the adverse-event entries list 15 participants at risk in each arm.

The registry reports no serious or other adverse events in the listed entries. It lists one outcome measure but no analysis records. Outcome estimates, statistical analyses, analysis populations, and missing-data methods are not reported in the registry record. Thus, the intended comparison and broad design are documented, but the primary result cannot be interpreted from the recorded information.