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 PHNA, Efficacy of Tretinoin Cream on Post-phototherapy Hyperpigmentation (NCT03933774), a randomized na study. The primary outcome is The Degree of Hyperpigmentation at 12 Weeks.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT03933774 |
| Phase | NA |
| Condition | Vitiligo |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Single |
| Enrollment | 25 |
| Arms in the primary outcome | n/a |
| Lead sponsor | The Catholic University of Korea |
| Results posted | Yes |
2. Clinical Question
The study asks whether applying tretinoin 0.05% cream to one half of the face during phototherapy is associated with less hyperpigmentation than applying placebo cream to the other half. The primary outcome is the degree of hyperpigmentation at 12 weeks, assessed using the L* value from Lab color space. A higher L* value indicates lighter skin and is described in the registry record as a better outcome.
Population
People with vitiligo. The registry record lists planned enrollment of 25 participants and describes the study as a pilot.
Intervention
Tretinoin 0.05% cream, applied once nightly for 1 month to one half of the face after randomization.
Comparator
Placebo cream, identified as PHYSIOGEL Daily Moisture Therapy Creme, applied once nightly for 1 month to the other half of the face.
Primary question
What is the degree of hyperpigmentation at 12 weeks, as assessed by L* value, in the treated and comparator areas?
The registry record does not report the observed L* values or a comparison between the areas. It also lists a secondary outcome concerning the number of participants with at least 75% repigmentation, but does not report its results. Consequently, the clinical question can be described from the registered aims, but the outcome evidence cannot be judged from the registry record.
3. Trial Design
The study is listed as randomized, single-masked, and parallel, with planned enrollment of 25. Its brief summary calls it a randomized controlled split-face pilot study. The intervention descriptions also specify application to opposite halves of the face: tretinoin on one side and placebo on the other. The registry record does not explain how the parallel classification relates to the split-face description or identify the unit used for randomization and analysis.
The tretinoin regimen is described as 25g of 0.05% cream for 1 month, applied once nightly. The comparator is described as 150ml of PHYSIOGEL Daily Moisture Therapy Creme for 1 month, also applied once nightly. The registry lists the study condition as vitiligo. The listed study status is completed; the recorded start date is 2019-04-29 and the primary completion date is 2019-11-19.
A split-face comparison can control for characteristics shared by the same participant, because both products are applied within that person. General statistical consideration: if outcomes from the two sides of a participant are analyzed, those measurements may be correlated. An analysis that treats them as independent could misrepresent uncertainty. The registry record does not report the analysis method or clarify whether the posted outcome analysis accounted for pairing.
The study is described as a pilot, but the registry record does not report a sample-size justification, a target effect size, or a detailed protocol rationale. It does not report whether the masked person was a participant, assessor, or another study role. Those details should not be inferred from the single-masked designation.
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
| Stage | Left Tretinoin 0.05% Cream, Right Placebo | Left Placebo, Right Tretinoin 0.05% Cream |
|---|---|---|
| STARTED | 12 | 13 |
| COMPLETED | 10 | 11 |
| NOT COMPLETED | 2 | 2 |
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 | Left Tretinoin 0.05% Cream, Right Placebo | Left Placebo, Right Tretinoin 0.05% Cream | Total |
|---|---|---|---|---|
| Participants analysed | 12 | 13 | 25 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 8 | 10 | 18 |
| Age, Categorical: >=65 years | Participants | 4 | 3 | 7 |
| Sex: Female, Male: Female | Participants | 7 | 4 | 11 |
| Sex: Female, Male: Male | Participants | 5 | 9 | 14 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Asian | Participants | 12 | 13 | 25 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Black or African American | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): White | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): More than one race | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 0 | 0 | 0 |
| Region of Enrollment: South Korea | participants | 12 | 13 | 25 |
| L* value at baseline | score on a scale | 58.5 (51 to 64) | 56.7 (50 to 63) | 57.6 (50 to 64) |
6. Primary Endpoint
The registry lists the primary outcome as The Degree of Hyperpigmentation at 12 Weeks, measured over at 12 weeks.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Full Range |
| Unit | score on a scale |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is the degree of hyperpigmentation at 12 weeks, measured as the L* value in Lab color space with a spectrophotometer. L* represents lightness on a scale from 0 to 100. The registry describes a higher score as indicating lighter skin and a better outcome.
Using a measured lightness value gives the study a numerical way to assess skin appearance at the stated follow-up time. A spectrophotometer is an instrument-based measure, rather than a rating described in the registry as a participant-reported outcome. General explanation: a continuous measurement can preserve gradations in an outcome, rather than reducing the observation to categories such as improved or not improved. The usefulness of that measurement still depends on how it is collected and analyzed, and those procedural details are not reported in the registry record.
The registry lists the endpoint as a mean with full-range dispersion. It does not report the observed means, ranges, or a numerical comparison of treatment areas. It also indicates that the primary outcome has several categories or time points and was not reduced to one comparison. Therefore, the endpoint’s intended meaning is clear, but its observed magnitude and precision are not reported in the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record identifies the intended comparison and the direction of the primary measure: higher L* values indicate lighter skin. It does not report the primary outcome values or a treatment comparison. The posted information therefore does not establish the size, direction, or precision of any observed difference in hyperpigmentation at 12 weeks.
The primary outcome is marked as having several categories or time points and not reduced to one comparison. This means that a single primary contrast cannot be described from the registry information used for this analysis. The record does not specify the individual categories or time points, nor does it report results for them. The secondary outcome—number of participants who showed at least 75% repigmentation—is named, but its observed count and comparison are also not reported in the registry record.
The listed enrollment is 25, and the adverse-event record lists 25 at risk in each of the two groups. Those entries do not provide the outcome-specific number analyzed or confirm how participant and facial-side counts relate to one another. The registry record does not report losses to follow-up, missing outcome measurements, or the analysis population for the primary outcome.
General explanation: an estimate describes the observed effect in the study, while a confidence interval describes the uncertainty around that estimate under the assumptions of the analysis. A p-value, when reported, summarizes how compatible the data are with a specified null model; it does not measure clinical importance. Neither an estimate nor its uncertainty can be evaluated without the relevant outcome results. No primary-outcome confidence interval or p-value is reported in the registry record.
The completed status indicates that the study is recorded as completed; it does not itself show that the primary outcome was measured, analyzed, or favorable. Likewise, a planned sample size or a planning illustration cannot substitute for observed results. The registry record does not provide enough information to determine whether the study found a difference, how large any difference was, or how precise it was.
The safety entries report no serious adverse events in either group and six other adverse events in the tretinoin group, compared with none in the placebo group. These figures describe the registry’s recorded safety counts; the record does not provide event descriptions or enough information to assess their nature, timing, or relationship to study treatment. They do not resolve the missing efficacy results.
9. Statistical Methods Explained
The study’s registry design is described as randomized, single-masked, and parallel, while the summary and application descriptions characterize the intervention as split-face. Randomization is intended, in general, to reduce systematic differences between comparison conditions by assigning treatment through a chance-based process. Masking is intended to limit the influence of knowledge about treatment assignment on behavior or assessment. The registry record does not identify who was masked, how randomization was carried out, or how the parallel design label was reconciled with application to opposite facial sides.
What does a split-face design imply for analysis?
General statistical explanation: when two areas from the same participant are compared, the measurements may share participant-level influences. Such paired observations are not necessarily independent. A paired analysis uses the within-person relationship; an independent-groups analysis assumes a different structure. The choice affects the estimated uncertainty and the interpretation of the comparison. The registry record does not report which approach was used, whether participant-level pairing was retained, or how the analysis handled the stated design.
The primary measure is a score on a 0 to 100 lightness scale, with higher values described as lighter skin. The registry specifies a mean and full-range dispersion. General explanation: a mean represents the average of measured values, while a range conveys the span from the lowest to highest observed value. These summaries do not by themselves show the distribution of values or the precision of a comparison. The observed summaries and comparative estimate are not reported in the registry record.
How should uncertainty be understood?
General statistical explanation: a confidence interval is a range of values compatible with the observed data under the method’s assumptions. A narrow interval indicates greater precision than a wide interval, but precision is distinct from whether an effect is important. A p-value summarizes compatibility with a specified null hypothesis under a statistical model; it does not state the probability that the null hypothesis is true. The registry record does not report a confidence interval or p-value for the primary endpoint, so these features cannot be assessed for this study.
The record’s sample-size assumptions describe a planning illustration based on the observed effect, using a two-sided significance level of 0.05, equal allocation, and a normal approximation. The stated planning effect is a fraction of the observed effect. Such calculations are planning illustrations, not observed power and not evidence that a target level of power was attained. The registry record does not report the trial’s own sample-size justification or the numerical planning results. It also does not report the observed effect used in that illustration in the information available for this analysis.
Why can over-dispersion matter?
General explanation: over-dispersion occurs when observed variability is greater than a statistical model assumes. If a model understates variability, its uncertainty estimates may be too small and its confidence intervals too narrow. This issue can arise in some count-data settings, but the registry record does not describe the primary outcome as a count outcome or report a model that can be evaluated for over-dispersion. No claim about over-dispersion in this study can therefore be made.
The registry marks the primary outcome as having several categories or time points and says it was not reduced to one comparison. General statistical explanation: a prespecified contrast can make clear which outcomes and time points are being tested, while examining several comparisons can raise multiplicity concerns. The registry record does not report the detailed set of comparisons, a multiplicity adjustment, an interim analysis plan, or a complete statistical analysis plan. Their absence from the record means their use cannot be confirmed or ruled out.
For outcomes with missing observations, general methods may use complete-case analysis, imputation, or models that make assumptions about the missingness process. Each approach has assumptions and can yield different results. The registry record does not report missingness or the method used to handle it. Because the primary results are not reported, the analysis method and its assumptions cannot be checked against the posted outcome findings.
10. Multiplicity, Missing Data and Analysis Populations
The registry record notes that the primary outcome has several categories or time points and was not reduced to one comparison. It does not identify the full set of primary comparisons, state which one was intended to be decisive, or report a multiplicity procedure. When several outcomes or time points are examined, general statistical practice distinguishes a prespecified primary contrast from exploratory comparisons. Adjustments or other approaches may be used to address the chance of false-positive findings across multiple tests, but the registry record does not report whether any such approach was planned or used.
The registry lists one secondary outcome: the number of participants who showed at least 75% repigmentation. It does not report the result for that outcome, how it was compared between conditions, or whether it was included in a multiplicity strategy. The record also does not report interim analyses or a detailed statistical plan.
Missing outcome data and analysis populations are not described. The record does not state how many participants completed follow-up, how many had a 12-week measurement, whether all randomized participants were analyzed, or how missing observations were handled. General explanation: exclusions and missing data can affect both the estimate and its uncertainty, particularly when the reasons for missingness relate to outcome or treatment. Without counts and methods, the possible impact cannot be assessed.
The registry’s enrollment entry is 25, but it does not give an outcome-specific analysis count. Its safety record lists 25 at risk in each group; these entries do not clarify the number of unique participants, facial sides, or observations included in the efficacy analysis. These details are not reported in the registry record.
11. 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 |
|---|---|---|---|
| Tretinoin 0.05% Cream Group | 0 | 25 | 0.0% |
| Placebo Cream Group | 0 | 25 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Tretinoin 0.05% Cream Group | 0 of 25 |
| Placebo Cream Group | 0 of 25 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Tretinoin 0.05% Cream Group | 6 of 25 |
| Placebo Cream Group | 0 of 25 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Tretinoin 0.05% Cream Group | Placebo Cream Group |
|---|---|---|---|
| Irritation | Skin and subcutaneous tissue disorders | 6 of 25 | 0 of 25 |
The registry lists zero serious adverse events in the tretinoin group and zero in the placebo group. For other adverse events, it lists six affected in the tretinoin group and zero in the placebo group. The record lists 25 at risk in each group for both the serious and other adverse-event entries.
These are counts recorded under the registry’s serious and other adverse-event categories. The registry record does not describe the events, their severity, timing, duration, or whether investigators considered them related to treatment. It also does not explain whether the figures count participants with at least one event or event occurrences, so those interpretations should not be assumed beyond the registry’s wording.
General explanation: zero recorded serious events does not establish that a treatment has no serious risks. Safety interpretation depends on the number and type of events, the amount of exposure, follow-up, and the completeness of reporting. The listed counts are descriptive and do not, by themselves, establish a causal relationship. The record does not provide enough detail to characterize the six other events or compare the overall safety profiles.
12. What the Result Does, and Does Not, Mean
The registry record describes a randomized pilot study intended to compare tretinoin cream with placebo cream for post-phototherapy hyperpigmentation in people with vitiligo. Treatment was described as once-nightly application for 1 month to opposite halves of the face. The planned primary assessment was the L* lightness value at 12 weeks, with higher values interpreted as lighter skin.
That description explains the study question, but the registry record does not report the primary outcome values or a numerical comparison. It also does not report results for the listed secondary outcome of at least 75% repigmentation. Thus, the posted information does not show whether the two conditions differed, the direction or size of a difference, or the precision of an estimate. No conclusion about efficacy can be drawn from the study description alone.
The safety record lists zero serious adverse events in each group and six other adverse events in the tretinoin group and zero in the placebo group. These counts do not establish cause or provide event details. They should be read as recorded safety information, not as a complete characterization of risks.
General explanation: a study result is most informative when its estimate, uncertainty, analysis population, and methods are available. Statistical significance alone, if reported, would not establish the importance of an effect; a non-significant result would not by itself establish equivalence. Neither interpretation can be made because the registry record does not report the relevant primary outcome comparison.
The study’s completed status and its planned enrollment do not fill that evidence gap. The registry record does not report the sample-size rationale, outcome-specific participation, missing-data handling, or detailed analysis plan. The results therefore remain uninterpretable as an efficacy comparison from the information recorded.
13. Why This Trial Matters Statistically
This trial is statistically notable because the registry combines a parallel-design classification with a split-face description. In a split-face comparison, the two treated areas belong to the same participant, so the dependence between observations can matter to the analysis. The record does not clarify the design classification or analysis structure. That uncertainty limits the ability to assess whether the statistical method matched the way treatment was applied.
The intended outcome is a measured lightness value, and the record states a clear direction for its interpretation: higher L* values mean lighter skin. Yet the primary results are not reported, and the registry notes that the outcome involved several categories or time points rather than one comparison. Without a defined reported contrast, readers cannot connect the measurement to an estimated effect or its precision.
The record also illustrates why enrollment and completion status are not substitutes for results. Planned enrollment is 25, but the outcome-specific analysis population, missing measurements, and statistical methods are not reported. The record describes a planning illustration based on an observed effect, but that does not establish observed power or replace a reported effect estimate.
General statistical lesson: useful interpretation requires more than a treatment description and an outcome definition. Readers need the analyzed observations, the comparison being estimated, uncertainty around the estimate, and enough information about the design and analysis to evaluate assumptions. Those details are not reported in the registry record for the primary efficacy outcome.
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 efficacy is that the registry record does not report the primary outcome results. It identifies the 12-week L* measure and its direction but gives no observed values, comparative estimate, or uncertainty measure. The stated handling of several categories or time points also leaves no single reported comparison to interpret.
The design description is not fully clear: the record classifies the study as parallel, while the summary describes a split-face study and the treatment instructions assign products to opposite sides of the face. It does not clarify the randomization unit, analysis unit, or whether the within-participant relationship was accounted for. These details matter for understanding the comparison and its uncertainty.
The record does not report outcome-specific analysis counts, follow-up completeness, missing-data methods, or analysis populations. It also does not give a detailed statistical plan, sample-size justification, multiplicity strategy, or interim analysis information. These omissions prevent assessment of how the planned outcomes were selected and analyzed.
The secondary outcome is named but has no reported result. Safety entries lack descriptions of the other adverse events and do not clarify their timing or relationship to treatment. Finally, a pilot description and planned enrollment of 25 do not establish that the study could precisely estimate the primary comparison. The registry record does not report a sample-size rationale or an efficacy estimate with which to assess precision.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: PHNA, Efficacy of Tretinoin Cream on Post-phototherapy Hyperpigmentation — NCT03933774.
- Registry record last updated 2020-08-18; status last verified 2020-08.
- Results first posted 2020-08-12.
- 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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Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
18. Record Summary
The completed study, NCT03933774, concerns tretinoin cream for post-phototherapy hyperpigmentation in people with vitiligo. The registry describes randomized allocation and single masking, and lists a parallel model; the summary and treatment instructions describe a split-face comparison. Planned enrollment is 25. Tretinoin 0.05% cream and placebo cream were described as applied nightly for 1 month to opposite sides of the face.
The primary outcome is the degree of hyperpigmentation at 12 weeks, measured by L* value, where higher scores indicate lighter skin. The registry says the primary outcome involved several categories or time points and was not reduced to one comparison. It does not report primary or secondary efficacy results. Safety entries list zero serious adverse events in each group and six other adverse events in the tretinoin group and zero in the placebo group. The registry record does not report event descriptions, missing-data handling, analysis populations, or a detailed statistical plan.