Racial/Ethnic Differences in Microneedle Response: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Racial/Ethnic Differences in Microneedle Response (NCT03332628), a na na study. The primary outcome is Micropore Closure Time.

2. Clinical Question

The study was intended to characterize skin barrier recovery after microneedle treatment in healthy people of differing racial and ethnic backgrounds. Its primary endpoint was micropore closure time, measured in hours. The endpoint description says that electrical resistance was measured daily with skin electrodes attached to an impedance meter, and that measurements collected over five days were used to calculate an average closure time. The reported endpoint was a mean with standard deviation.

The question is descriptive and comparative across participant subsets. It is not a comparison of microneedle application against an untreated or alternative-treatment group. Consequently, differences between subsets, if reported, would describe variation within this study population; they would not by themselves establish why any difference occurred. The registry record does not report the actual mean closure times, their standard deviations, or estimates of differences between subsets. It therefore does not permit a conclusion about the direction or size of any racial or ethnic differences.

3. Trial Design

NCT03332628, titled “Racial/Ethnic Differences in Microneedle Response,” is a completed study sponsored by the University of Iowa. Its official title describes evaluation of racial and ethnic differences in micropore closure rates after microneedle application to the skin. The record identifies the condition as healthy and lists the intervention as a microneedle patch.

The design is listed as single-group, with no allocation and no masking. All participants completed the only study arm, called Microneedle application. The arm description states that nine upper-arm sites were identified, baseline measurements were made at each site, and the sites were divided into clusters of three. The description available in the registry record ends before it fully explains what was done at each cluster, so details beyond those statements are not reported in the registry record.

The registry lists enrollment of 132. For the primary outcome, it says data from all 111 participants were analyzed and notes that subgroup row counts differ from the overall number because results are reported by racial and ethnic subgroup. The record does not explain the difference between enrollment and the primary-outcome analysis population, or provide the subgroup counts in the information.

The study started on 2018-02-01 and reached primary completion on 2019-11-01. Its status is completed. The primary outcome timeframe is five days. Secondary outcomes listed in the registry are change in trans-epidermal water loss, skin color, and hydration. The record lists four outcome measures, but it does not report the numerical primary outcome results or the results of statistical analyses. The registry record does not describe a randomized control comparison, and the single-group structure should be kept in view when interpreting any comparison between participant subsets.

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: Subjects were screened after consenting to participate in the study. Participants that did not meet screening criteria were withdrawn from the study, 5 of our 132 consented participants fell into this exclusionary criteria. 9 of 132 participants signed the consent and stopped returning communication with study staff prior to scheduling their appointments, they were withdrawn from the study due to lack of follow-up. 5 of 132 voluntarily withdrew consent because of schedule conflicts.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Data from all 111 participants was analyzed. The number in each row differs from the overall number because results are reported according to racial and ethnic subgroups.

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 Micropore Closure Time, measured over Five days.

The primary endpoint is micropore closure time, measured in hours. It represents the time required for the skin barrier to be restored after microneedle application. The registry describes electrical resistance as the measurement used to assess that recovery: skin electrodes attached to an impedance meter were used to measure electrical resistance daily, and the collected measurements over five days were used to calculate an average closure time.

This endpoint is useful for the stated research question because it translates repeated skin measurements into a continuous measure of recovery time. A mean summarizes the average closure time in a group or subgroup. The standard deviation describes how much individual measurements vary around that mean; it is not a measure of uncertainty in the mean itself. As a general statistical distinction, a confidence interval would communicate uncertainty around an estimated mean or difference, while a standard deviation describes participant-level spread.

The registry record identifies the endpoint’s unit, summary measure, dispersion measure, and timeframe, but it does not report the means or standard deviations. It also does not report confidence intervals, subgroup contrasts, or a statistical test for this endpoint. Thus, the endpoint definition is available, but the magnitude and precision of the observed closure times cannot be assessed from the reported information.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a continuous primary endpoint: mean micropore closure time in hours, with standard deviation as the measure of dispersion. The endpoint was derived from repeated electrical resistance measurements taken during the five-day timeframe. The description gives the intended measurement approach, but the registry record does not report the numerical outcome data, a statistical model, or the analyses used to compare participant subsets.

What does a mean represent?

As a general statistical concept, a mean is the arithmetic average of the observed values in a group. For this endpoint, it would summarize average closure time among participants whose data contributed to the relevant estimate. A mean is easy to interpret in the endpoint’s stated unit, hours, but it does not show the range of individual experiences or the shape of the distribution. Different sets of observations can have the same mean while differing substantially in their spread or distribution.

The registry identifies standard deviation as the dispersion measure. In general, standard deviation describes how far observations tend to lie from the mean. It is distinct from the standard error, which describes the sampling uncertainty of an estimated mean. A standard deviation can help readers understand participant-to-participant variability, but it does not alone show how precisely the mean has been estimated. Neither numerical standard deviations nor standard errors are reported for the primary endpoint in the registry record.

Why does the repeated measurement matter?

The endpoint description says electrical resistance was measured daily using skin electrodes and an impedance meter, and that data collected across five days were used to calculate an average closure time. Repeated measurements can provide information about the course of recovery rather than relying on one observation. In general, repeated observations from the same participant are related, so an analysis of the full measurement sequence may need to account for within-participant dependence. The registry does not report whether such a model was used, or whether the analysis instead relied only on a derived average closure time.

The record describes closure time as an average calculated using the collected data. It does not provide the precise calculation rule for translating the daily electrical resistance readings into a closure time, the criteria for determining restoration of the skin barrier, or rules for measurements that were unavailable or difficult to interpret. Those details are not reported in the registry record. Without them, the measurement process cannot be fully reproduced from the registry description alone.

What would a subgroup comparison show?

The stated purpose includes comparing micropore closure time between subsets of participants based on race and ethnicity. In general, a difference between subgroup means describes the contrast between the observed group averages. Its interpretation depends on the subgroup definitions, the number of observations in each group, the amount of variability, and the method used to account for uncertainty. The registry information does not give the subgroup labels or counts, estimated means, contrasts, confidence intervals, p-values, or a description of covariate adjustment.

Because the study is single-group and has no allocation, such a comparison is not a randomized treatment contrast. It can describe observed differences within the study, but it cannot by itself separate the effect of race or ethnicity from other characteristics that may differ between participants. The registry record does not report whether potential confounders were measured or included in an adjusted analysis. It also does not report the statistical method used for subgroup comparisons.

How should uncertainty be read?

In general, a confidence interval gives a range of values compatible with the data under the assumptions of the analysis. A narrow interval indicates greater precision than a wide interval, though the interval’s meaning still depends on the validity of the study design and analysis. A p-value, when reported, addresses compatibility of the data with a specified statistical null model; it does not quantify the size or practical importance of a difference. Neither confidence intervals nor p-values for the primary outcome are reported in the registry record. The absence of those estimates means there is no basis to characterize the precision or statistical evidence for subgroup differences.

Sample-size calculations can be used for planning, but their assumptions should not be confused with observed trial results. The stated planning illustration assumes a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the target effect expressed as a stated fraction of the observed effect. It is described as an illustration computed from the observed effect, not as the study’s own design. This hypothetical two-arm planning framework is distinct from the actual single-group study. No sample-size justification for the study itself is reported in the registry record, and no planning-illustration values are included in the information. Such planning figures, even when available, would not be observed power or evidence that a result was detected.

More broadly, statistical methods cannot be reconstructed from an endpoint definition alone. The registry record does not report the primary analysis procedure, whether tests were one- or two-sided for the outcome analysis, how subgroup contrasts were estimated, whether any assumptions were checked, or how multiplicity was handled. These omissions leave the analysis approach and the robustness of any result unassessable from the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary outcome and secondary outcomes involving change in trans-epidermal water loss, skin color, and hydration. It does not report a multiplicity strategy, such as a prespecified hierarchy of tests or an adjustment for making several comparisons. As a general statistical matter, evaluating multiple outcomes or subgroup contrasts can increase the chance of finding at least one apparently unusual result by chance. The registry record does not provide enough information to determine how that issue was addressed.

Missing-data handling is also not reported in the registry record. The primary endpoint description refers to measurements collected over five days, but does not explain how incomplete daily measurements were handled, how closure time was calculated when observations were missing, or whether imputation or another method was used. The record states that data from 111 participants were analyzed, while enrollment was 132, but does not explain the difference or describe the participants excluded from the primary analysis.

The record does not define an intention-to-treat, per-protocol, or other analysis population. It gives the number analyzed for the primary outcome and notes that subgroup row counts differ because the results are organized by racial and ethnic subgroup. Without subgroup counts and a clear account of exclusions, the composition of each analysis set cannot be evaluated. The registry record also does not describe sensitivity analyses or procedures for assessing whether missingness could have affected the findings.

These gaps matter because outcome availability and analysis choices can affect both the estimate and its uncertainty. The registry record does not report enough information to assess whether missing measurements, multiple outcomes, or subgroup analyses influenced the interpretation.

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 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry reports safety counts for the Microneedle Application group. The serious-event count was zero among 113 participants at risk. The count of other, non-serious events was one among 113 participants at risk, and deaths were zero. These are counts, not estimates of risk differences against a control group.

The study had a single group, so the figures do not provide a randomized comparison with an untreated or alternative-treatment group. In general, a count of zero serious events in a study group does not establish that an event cannot occur; it describes what was recorded among the participants at risk during the reporting period. The registry record does not report a comparison group, event-specific follow-up details, or a fuller description of the one other event. It lists no serious-event terms.

The safety denominator is 113 participants at risk, distinct from enrollment of 132 and the 111 participants reported in the primary-outcome analysis. The registry record does not explain the difference among these counts. The safety figures should therefore be read as the registry’s reported event counts and denominator, not as evidence about comparative safety or as a complete account of events outside the reported categories.

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

The study addresses a clearly stated measurement question: the time needed for skin barrier recovery after microneedle application, assessed through electrical resistance measurements over five days. It also aims to compare average closure time across racial and ethnic subsets of healthy participants. The single-group design is consistent with describing responses after application and examining subgroup patterns, but it does not provide a randomized control comparison.

The registry record does not report the primary outcome estimates. There are no reported means, standard deviations, subgroup contrasts, confidence intervals, or p-values in the information. As a result, it is not possible to say whether closure time was shorter or longer in any subset, how large any difference was, or how precise an estimate might be. The record therefore does not support a conclusion about whether racial or ethnic differences were observed.

Even if subgroup estimates were available, a difference in observed group averages would not alone establish its cause. In general, participant characteristics and study conditions can vary across subgroups, and a single-group observational comparison does not randomize those characteristics. The registry record does not describe an adjusted analysis or identify factors considered as potential explanations for subgroup differences.

The reported safety counts describe events recorded in the study group, with no serious events and one other event among 113 participants at risk; deaths were zero. Without a control group, these counts do not establish comparative safety. They also do not replace a detailed account of event types and follow-up.

The central distinction is between an outcome being defined and an outcome result being reported. This record describes how micropore closure time was intended to be measured and identifies the analysis population, but does not provide numerical results with which to judge the observed response. Interpretation must remain limited to the design, endpoint, and counts that the registry reports.

13. Why This Trial Matters Statistically

This study is statistically notable for focusing on measurement of skin barrier recovery after microneedle application and for asking whether the response varies across racial and ethnic subsets. Its endpoint is continuous and expressed in hours, making the target quantity conceptually direct: average time to micropore closure. The use of repeated electrical resistance measurements is also relevant because the endpoint concerns a process over time rather than a single isolated measurement.

The study’s single-group structure shapes what its comparisons can establish. The registry describes one arm completed by all participants and subgroup comparisons based on race and ethnicity. This permits a descriptive question about variation in measured closure time within the study population, but it is not a randomized comparison of different treatments. Statistical interpretation needs to keep that distinction clear.

The record also highlights the importance of separating enrollment from the analysis population. It reports enrollment of 132 and primary-outcome data from 111 participants, while noting that subgroup row counts vary. Without a reported explanation for these counts or the numerical subgroup estimates, readers cannot assess the distribution of information across groups or the precision of comparisons.

Finally, the record illustrates why endpoint definitions and numerical results serve different purposes. A detailed description of what was to be measured helps clarify the scientific question; without reported estimates and uncertainty, however, it does not answer that question. The absence of primary outcome results and analysis details limits statistical interpretation, regardless of the study’s completed status.

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 statistical interpretation is that the registry record does not report numerical results for the primary endpoint. Means, standard deviations, subgroup contrasts, confidence intervals, and p-values are not reported in the registry record. The direction, magnitude, and precision of any subgroup difference therefore cannot be assessed.

The study is a single-group design with no randomized allocation or separate control arm. Comparisons described between racial and ethnic subsets are not randomized contrasts, so they cannot by themselves distinguish subgroup association from other differences between participants. The registry record does not report adjustment for potential confounders or specify which participant characteristics were considered.

The primary analysis population is described as 111 participants, compared with enrollment of 132. The reason for this difference is not reported in the registry record. Although the record notes that subgroup row counts differ, it does not give the subgroup counts in the information. This leaves uncertainty about completeness and representation in the outcome analysis.

The endpoint description gives the measurement instrument, daily measurement approach, timeframe, and summary statistic, but does not fully specify how electrical resistance readings were converted into closure time or how incomplete measurement sequences were handled. The arm description also ends before all procedures are detailed. These procedural details are not reported in the registry record.

The registry does not report the analysis method, multiplicity handling, missing-data approach, or a statistical analysis population definition. It also does not report a study-specific sample-size justification. The stated planning illustration is not the study’s design and cannot substitute for those details. Together, these limitations prevent a complete assessment of how the primary outcome was analyzed or how robust any result might be.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Racial/Ethnic Differences in Microneedle Response — NCT03332628.
• Registry record last updated 2021-02-15; status last verified 2021-02.
• Results first posted 2021-02-15.
• 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.

18. Record Summary

NCT03332628 is a completed, University of Iowa-sponsored, single-group study titled “Racial/Ethnic Differences in Microneedle Response.” It enrolled 132 healthy participants and evaluated skin barrier recovery after microneedle application. The primary outcome was mean micropore closure time in hours, assessed using daily electrical resistance measurements over five days. The record reports that data from 111 participants were analyzed for this outcome, with subgroup row counts varying.

The study had no allocation and no masking. Its only arm involved microneedle application at upper-arm sites. The registry lists secondary outcomes of change in trans-epidermal water loss, skin color, and hydration. Safety counts include zero serious events, one other event, and zero deaths among 113 participants at risk.

Numerical primary outcome estimates and statistical analyses are not reported in the registry record. The record also does not explain the difference between enrollment and primary-outcome analysis or describe missing-data and multiplicity methods.