Epidermal Grafting in Wound Healing: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Epidermal Grafting in Wound Healing (NCT02535481), a randomized na study. The primary outcome is Number of Wounds With Complete Healing.

2. Clinical Question

The clinical question was whether wound-healing outcomes differed between epidermal grafting and split thickness skin grafting. The registry summary also describes an interest in the mechanisms by which each technique may achieve healing. It proposes that epidermal grafting may promote healing through growth factors and keratinocyte migration, whereas split thickness grafting provides a skin covering that integrates with the wound bed. These are explanations of the rationale in the registry summary, not findings established by the reported trial results.

3. Trial Design

The registry describes a multicentre randomized controlled trial with parallel groups and no masking. Participants were assigned to epidermal grafting or split thickness skin grafting. The listed enrollment is 44. The registry lists 22 participants at risk in each group for the adverse-event summaries. The trial is marked completed, and its phase is listed as NA.

The trial title and registry summary identify wound healing as the focus. The stated primary outcome is the number of wounds with complete healing. The outcome timeframe is given as 6 weeks and 3 months, while its description specifies complete healing at 6 weeks. Secondary outcomes include time for wound healing, donor site morbidity, a patient-reported outcome measure, and adverse events. The record lists 6 outcome measures and 7 analyses, but does not provide enough detail to reconstruct which analyses correspond to each measure.

The intervention descriptions refer to procedures carried out according to normal clinical practice. The registry does not report additional details about allocation concealment, the randomization sequence, eligibility criteria, follow-up procedures, or whether outcome assessment was independent of treatment assignment. The dates recorded are a study start of 2015-10 and primary completion of 2017-08. University College, London is listed as sponsor.

Information about the protocol’s statistical plan, including any prespecified model or approach to comparing healing outcomes, is not reported in the registry record. The enrollment figure alone does not establish how the target enrollment was chosen. A sample-size justification for the trial is 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.

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 Number of Wounds With Complete Healing, measured over 6 weeks and 3 months.

The primary endpoint is titled “Number of Wounds With Complete Healing.” It measures a count of wounds that met the registry’s complete-healing criterion at the specified assessment time. The outcome description identifies 6 weeks; the listed timeframe also includes 3 months. The registry does not explain how complete healing was defined or how the two listed time points relate to the primary outcome.

Counting healed wounds provides a direct way to describe the occurrence of complete healing in the study groups. In general, an outcome like this can be used to compare the number of events across assigned groups. The interpretation depends on how the count was collected, the number of wounds assessed, whether participants could contribute more than one wound, and how missing assessments were handled. Those details are not reported in the registry record.

The endpoint title does not itself state a comparison or establish a treatment effect. The registry record does not report the group-specific healing counts, the denominators for the primary endpoint, or an effect estimate with uncertainty. It also does not report whether an analysis accounted for differences in the number of wounds per participant. Consequently, the primary endpoint’s comparative result and its precision cannot be assessed from the posted information.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The trial is recorded as randomized, parallel, and unmasked. Randomization is a design method intended to make assigned groups comparable, on average, with respect to factors that could affect outcomes. It does not guarantee that every measured or unmeasured characteristic is balanced in a particular trial. The registry record does not describe the sequence-generation method or allocation concealment, so those aspects of the randomization process cannot be evaluated.

What does a count endpoint represent?

The primary outcome is a count: the number of wounds with complete healing. A count is different from a continuous measurement, such as a measurement on a scale, and it is not automatically a proportion. To interpret a count, readers need its denominator and the rules used to identify eligible wounds and healed wounds. They also need to know how many wounds were assessed and whether a participant could contribute multiple wounds. These details are not reported in the registry record.

As general statistical context, an analysis of counts may need to account for the amount of opportunity to observe events. A count of healed wounds is difficult to compare fairly if groups differ in the number of wounds assessed. If multiple wounds belong to the same participant, outcomes from those wounds may be related rather than independent. An analysis that treats related observations as independent can give misleading uncertainty. The registry record does not state whether participants contributed multiple wounds or how any such relationship was handled.

How would uncertainty be described?

As general statistical context, an effect estimate describes the size and direction of a comparison, while a confidence interval describes the range of values compatible with the data under the assumptions of the analysis. A narrow interval indicates greater precision than a wide interval; neither an estimate nor its interval alone resolves concerns about outcome measurement, missing data, or analysis choices. The registry record does not report a primary-outcome estimate or confidence interval, so the precision of the comparison cannot be assessed.

A p-value, when reported, addresses how compatible the observed data are with a specified statistical model and a stated null hypothesis. It does not measure the size or clinical importance of an effect. No primary-outcome p-value or statistical test is reported in the registry record. No claim about statistical significance can therefore be made from the posted primary-outcome information.

What does the design tell the reader?

The parallel design means that the study compares groups assigned to different grafting approaches. The registry says there was no masking. In general, lack of masking can matter when outcomes involve judgment, participant reports, or decisions about assessment. Complete wound healing may depend on how the outcome is defined and assessed. The registry record does not say who assessed healing or whether standardized criteria were used, so the potential influence of unmasked assessment cannot be evaluated.

The summary describes the trial as multicentre, but the number of participating centres and how centre effects were handled are not reported in the registry record. The primary endpoint is framed as a wound count, and the record does not state whether the analysis considered centre, participant-level clustering, or other covariates. It would be inappropriate to assume a particular statistical model or adjustment strategy.

What can be inferred from the planning assumptions?

The record describes a planning illustration based on an observed effect, with a two-sided significance level of 0.05, equal allocation between groups, and a normal approximation. It says the effect to detect is a stated fraction of the observed effect. These are planning assumptions, not evidence that the trial was designed using those assumptions. The sample-size justification for the trial itself is not reported in the registry record, and the illustration should not be read as observed power.

In general, power is a design-stage probability tied to assumptions about an effect, variability, outcome frequency, and analysis. It is not a post-trial measure of whether a result is trustworthy. A planning calculation using an observed effect is especially unsuitable as a substitute for the trial’s prespecified design rationale. No sample-size illustration values are reported in the registry record, so no numerical planning result can be interpreted.

The registry lists 6 outcome measures and 7 analyses. Those counts do not specify which analysis was primary, how analyses were selected, or whether tests were adjusted for multiple comparisons. The statistical analysis plan, model specification, handling of missing outcome data, and analysis population are not reported in the registry record. These omissions prevent a detailed evaluation of the methods used to estimate the trial’s treatment contrast.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 6 outcome measures and 7 analyses. It identifies a primary outcome but does not report how the analyses were assigned to the outcome measures, whether additional time points or subgroups were examined, or which results were prespecified. A plan for handling multiple statistical comparisons is not reported in the registry record.

As general statistical context, testing several outcomes or time points can increase the chance of a nominally unusual result if each is considered separately. Methods for addressing this issue depend on the analysis plan and the purpose of the comparisons. Without the prespecified plan and analysis details, it is not possible to determine whether multiplicity was considered or to interpret any unreported analysis accordingly.

Missing-data methods are not reported in the registry record. The record does not state how missing wound assessments, withdrawals, or incomplete follow-up were handled. It also does not describe the primary analysis population, such as whether participants were analyzed according to their randomized assignment. These details matter because exclusions and missing outcomes can affect both the estimated comparison and its uncertainty.

The primary outcome results and denominators are not reported in the registry record. Without them, readers cannot assess completeness of follow-up for the primary endpoint or determine whether the reported result, if any, included all randomized participants. No assumptions about missingness or imputation can be made from the information recorded.

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.

For the epidermal graft group, the registry records 0 serious adverse events among 22 at risk, 0 other adverse events among 22 at risk, and 0 deaths. For the split thickness skin graft group, it records 0 serious adverse events among 22 at risk, 0 other adverse events among 22 at risk, and 0 deaths. These figures describe the event counts in the registry’s safety fields.

A count of 0 means that no event was recorded in that field; it does not establish that no event could occur or that all possible events were captured. The record does not report detailed definitions for serious and other events, the follow-up period for safety, or the procedures used to collect and verify events. It also does not provide event-specific descriptions because no serious-event terms are listed.

As general statistical context, a zero event count does not remove uncertainty about the underlying risk. Interpretation depends on the amount and duration of observation and the completeness of reporting. These registry figures should therefore be read as a limited safety summary, not as proof of equivalent safety between procedures.

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

The record establishes that a randomized, parallel, unmasked trial compared epidermal grafting with split thickness skin grafting. It specifies complete wound healing as the primary outcome and identifies additional outcomes related to healing time, donor site morbidity, patient-reported outcomes, and adverse events. These details define the research question and the intended areas of comparison.

The record does not report the primary outcome counts or a comparative estimate. It therefore cannot show whether either group had more wounds completely healed, how large a difference might have been, or how precisely a difference was estimated. The listed timeframe includes 6 weeks and 3 months, but the outcome description refers specifically to 6 weeks; results and clarification of that timing are not reported in the registry record.

The registry’s safety summary records no serious adverse events, other adverse events, or deaths in either group. This is a description of the entries in the record, not evidence that the approaches have identical safety or that rare events are impossible. The extent and duration of safety surveillance are not reported.

The brief summary presents possible differences in how the grafting approaches might promote healing. These descriptions are rationale for the research question and do not establish a mechanism demonstrated by the trial. Likewise, the presence of secondary outcomes does not establish their results.

In general, a randomized design can support a causal comparison when outcomes are measured and analyzed according to sound methods. Here, the design information is not accompanied by reported primary results, analysis details, or uncertainty estimates. The registry record consequently supports a description of what the trial set out to compare, but not a conclusion about the comparative effect of the procedures.

13. Why This Trial Matters Statistically

This trial’s statistical question is not simply whether wounds heal, but how to compare healing under two grafting approaches using a clearly defined outcome and appropriate denominators. Naming the endpoint as a count of completely healed wounds signals that readers need information about the number of wounds assessed and the rule for classifying complete healing. Those details are essential for interpreting a count as a comparison.

The registry also lists more than one outcome measure and more analyses than outcome measures. That makes transparent prespecification important: readers need to know which outcome and time point were primary, which analyses were planned, and how results were selected for reporting. The record identifies a primary outcome but does not provide enough analysis detail to evaluate these issues.

As general statistical context, wounds belonging to the same participant may have correlated outcomes. Counts may also depend on how many wounds are observed in each group. A sound analysis should match the structure of the data and explain how it accounts for these features. The registry does not report whether participants contributed multiple wounds or how the analysis handled the count structure.

The unmasked design is another reason that clear outcome definitions and assessment procedures matter. Reporting who judged healing and how assessments were standardized would help readers understand the potential for assessment effects. Such details are not reported in the registry record.

Most importantly, a trial’s design and rationale cannot replace its outcome results. Without group-specific healing counts, denominators, an effect estimate, and a measure of uncertainty, the central comparative question remains unanswered in the registry record. The posted information is therefore useful for defining the intended comparison, while leaving the principal statistical result unavailable.

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 main limitation for interpreting this trial is that the primary-outcome results are not reported in the registry record. No group-specific counts of wounds completely healed, endpoint denominators, comparative estimate, confidence interval, or p-value are given. The record itself indicates that the primary outcome has several categories or time points and was not reduced to a single comparison. As a result, the central comparison cannot be reconstructed from the posted information.

The timeframe is not fully clear: the registry lists 6 weeks and 3 months, while the outcome description specifies complete healing at 6 weeks. The record does not explain the relationship between those time points or provide results for either. The definition and assessment procedure for complete healing are also not reported.

Important design and analysis details are absent. The registry does not report eligibility criteria, allocation concealment, the randomization method, the primary analysis population, handling of missing data, or the statistical model. It does not say whether multiple wounds per participant were possible or how any dependence between wounds was addressed. The number of centres and any centre-level analysis are not reported in the registry record.

The record lists multiple outcomes and analyses but does not report a multiplicity strategy or distinguish the planned analyses from other analyses. The sample-size justification for the trial itself is not reported. These gaps limit assessment of the potential for selective reporting, precision, and robustness. The safety summary is also limited by the absence of detailed event definitions and follow-up information.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Epidermal Grafting in Wound Healing — NCT02535481.
• Registry record last updated 2020-08-10; status last verified 2020-07.
• Results first posted 2020-08-10.
• 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 describes a completed, multicentre, randomized, parallel, unmasked trial of epidermal grafting versus split thickness skin grafting. Enrollment is listed as 44. The recorded study start is 2015-10 and primary completion is 2017-08; the sponsor is University College, London.

The primary outcome is the number of wounds with complete healing, with a listed timeframe of 6 weeks and 3 months. The outcome description specifies complete healing at 6 weeks. The primary-outcome results are not reported in the registry record. Secondary outcomes concern time for wound healing, donor site morbidity, patient-reported outcomes, and adverse events.

The adverse-event fields record 0 serious events, 0 other events, and 0 deaths in each group, with 22 at risk in each group. Detailed statistical methods, missing-data handling, and the trial’s sample-size justification are not reported in the registry record.