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 Comparing a Novel Phototherapy Kiosk to Oral Vitamin D Supplementation (NCT04556136), a randomized na study. The primary outcome is Serum Vitamin D Level.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT04556136 |
| Phase | NA |
| Condition | Hypovitaminosis D |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Triple |
| Enrollment | 106 |
| Arms in the primary outcome | 2 |
| Lead sponsor | Madigan Army Medical Center |
| Results posted | Yes |
2. Clinical Question
Population
The trial concerned volunteers with hypovitaminosis D. The registry describes participants with various baseline levels of 25(OH)D. The primary outcome description says the final sample included 43 participants in the SPK group and 45 in the Oral Supplement group. It also says 10 subjects of 98 enrolled dropped out before the end of the study. The registry lists total enrollment as 106; it does not explain how that figure relates to the primary outcome description.
Intervention
Participants assigned to the standing phototherapy kiosk (SPK) group received kiosk phototherapy once every other week for 10 weeks. Treatment dose was based on self-reported Fitzpatrick skin type. The registry describes the treatment as usually lasting no more than 10 minutes. Its brief summary describes two approximately 2-minute treatments per month, so the precise treatment duration is not presented consistently across the record.
Comparator
The comparison group took one 600 IU oral vitamin D3 supplement each day for 10 weeks, with a meal. The arm description says participants received a 10-week supply of 70 pills. The comparison therefore concerns two different delivery approaches over the same stated intervention period, rather than different doses of the same delivery method.
Primary question
The primary outcome was serum 25 Hydroxyvitamin D level at 10 weeks, measured in ng/mL. The registry labels its reported two-arm analysis as non-inferiority and names the Wilcoxon (Mann-Whitney) method, with p = 0.01. The non-inferiority margin and the direction of the formal hypothesis are not reported in the registry record. The observed summaries describe the final groups; they do not, by themselves, establish the interpretation of a non-inferiority test.
3. Trial Design
This was a randomized, parallel-group trial with triple masking recorded in the registry. Its listed phase is NA, and its status is completed. The registry names Madigan Army Medical Center as sponsor. The stated start date is 2018-04-30 and the primary completion date is 2019-01-22.
The registry lists enrollment as 106. The brief summary describes a plan to assign approximately 120 volunteers to one of two groups, while the primary outcome description states that 98 were enrolled for that outcome and that 10 dropped out before the end of the study. These figures are recorded in different parts of the registry; an explanation reconciling them is not reported in the registry record. The primary outcome summaries use a final sample of 43 in the SPK group and 45 in the Oral Supplement group.
The SPK group attended phototherapy sessions every other week for 10 weeks. The dose was based on Fitzpatrick skin type. The oral group took a 600 IU vitamin D3 pill each day for 10 weeks, with a meal. The trial’s stated purpose was to assess the kiosk’s capability to stimulate vitamin D production and compare serum 25 Hydroxyvitamin D levels with those in the oral supplement group.
The registry lists two secondary outcomes: device acceptability using the Device Usability Scale, and the number of subjects retained at 14 weeks. It lists five outcome measures overall, but only two secondary outcomes in the posted record. Further details on allocation procedures, how masking was implemented, and the statistical analysis plan are not reported in the registry record.
4. Participant Flow and Accounting
The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.
Before assignment: No pre-assignment activities.
Overall Study
| Stage | Standing Phototherapy Kiosk (SPK) | Oral Supplement |
|---|---|---|
| STARTED | 53 | 53 |
| COMPLETED | 43 | 45 |
| NOT COMPLETED | 10 | 8 |
Reasons for not completing this period:
| Reason | Standing Phototherapy Kiosk (SPK) | Oral Supplement |
|---|---|---|
| Lost to Follow-up | 6 | 6 |
| Physician Decision | 2 | 1 |
| Withdrawal by Subject | 2 | 1 |
Analysis population for the primary outcome, as defined in the registry: Final sample included 43 in SPK and 45 in Oral Supplement group; 10 subjects of 98 enrolled dropped out prior to the end of the 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.
| Characteristic | Unit | Standing Phototherapy Kiosk (SPK) | Oral Supplement | Total |
|---|---|---|---|---|
| Participants analysed | 53 | 53 | 106 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 52 | 49 | 101 |
| Age, Categorical: >=65 years | Participants | 1 | 4 | 5 |
| Sex: Female, Male: Female | Participants | 32 | 25 | 57 |
| Sex: Female, Male: Male | Participants | 11 | 20 | 31 |
| Ethnicity (NIH/OMB): Hispanic or Latino | Participants | 7 | 8 | 15 |
| Ethnicity (NIH/OMB): Not Hispanic or Latino | Participants | 36 | 37 | 73 |
| Ethnicity (NIH/OMB): Unknown or Not Reported | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Asian | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Black or African American | Participants | 5 | 7 | 12 |
| Race (NIH/OMB): White | Participants | 27 | 20 | 47 |
| Race (NIH/OMB): More than one race | Participants | 7 | 8 | 15 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 4 | 10 | 14 |
| Region of Enrollment: United States | participants | 43 | 45 | 88 |
| Marital status: Single | Participants | 8 | 12 | 20 |
| Marital status: Married | Participants | 35 | 33 | 68 |
| Military affiliation: Active duty | Participants | 22 | 28 | 50 |
| Military affiliation: Retired or prior service | Participants | 11 | 8 | 19 |
| Military affiliation: Family member | Participants | 8 | 6 | 14 |
| Military affiliation: None | Participants | 2 | 3 | 5 |
6. Primary Endpoint
The registry lists the primary outcome as Serum Vitamin D Level, measured over 10 weeks.
| Element | Registry entry |
|---|---|
| Result type | Median |
| Measure of spread | Inter-Quartile Range |
| Unit | ng/mL |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint was serum vitamin D level, specifically 25 Hydroxyvitamin D in blood, measured at 10 weeks and expressed in ng/mL. The registry reports the endpoint using the median and inter-quartile range for each group. This describes the distribution’s central value and the spread of the middle portion of observed values, respectively.
Serum 25 Hydroxyvitamin D is the direct laboratory measure selected to address the trial’s stated question about whether kiosk phototherapy stimulates vitamin D production compared with daily oral supplementation. The endpoint is a biological measurement, not a direct measure of symptoms, quality of life, or longer-term clinical outcomes. The record does not report such outcomes as primary endpoints.
The reported median was 30.0 ng/mL in the SPK group, with an inter-quartile range from 25.8 to 37.0, and 25.5 ng/mL in the Oral Supplement group, with an inter-quartile range from 21.0 to 29.8. These are summaries of the final groups at the stated time point. The registry does not report a confidence interval for the difference or a baseline-adjusted estimate. It also does not explain whether the primary endpoint was analyzed as a change from baseline or as a 10-week value alone.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
At 10 weeks, the observed median serum vitamin D level was 30.0 ng/mL in the SPK group and 25.5 ng/mL in the Oral Supplement group. The respective inter-quartile ranges were 25.8 to 37.0 and 21.0 to 29.8. These summaries describe the participants included in the final outcome groups, not necessarily all randomized participants.
The registry reports a Wilcoxon (Mann-Whitney) analysis with p = 0.01 and labels the analysis as non-inferiority. This p-value is evidence that the data were not equally distributed under the test’s null hypothesis, given the test’s assumptions. It does not quantify the size or clinical importance of a difference. Nor does it, by itself, demonstrate non-inferiority. A non-inferiority conclusion depends on a prespecified margin, the test’s direction and hypothesis, and a suitable estimate with uncertainty. The margin and supporting estimate are not reported in the registry record.
The observed group medians are higher in the SPK group, but the medians alone do not reveal the full distributions or quantify uncertainty in a between-group contrast. The posted inter-quartile ranges convey within-group spread; they are not confidence intervals for a treatment effect. No confidence interval, test statistic, or adjusted comparison estimate is reported in the registry record.
The final outcome groups contain 43 SPK participants and 45 Oral Supplement participants. The endpoint description also states that 10 of 98 enrolled subjects dropped out before study end. The registry does not report the reasons for dropout, group-specific missingness, or the method used to handle missing endpoint values. These omissions make it difficult to assess whether the final-group comparison represents the randomized groups without bias.
The p-value should therefore be read alongside the observed distributions and the missing methodological details. The posted result indicates a statistically detectable difference under the reported rank-based test, while the available record does not establish the precise size or uncertainty of that difference or allow independent evaluation of the non-inferiority claim. The result applies to this 10-week pilot comparison and its observed participants, not automatically to other settings or longer follow-up.
9. Statistical Methods Explained
What does the reported Wilcoxon test compare?
The registry names the Wilcoxon (Mann-Whitney) method for the two-group analysis. In general, this rank-based method compares the relative ordering of observations across groups. It does not require the outcome to follow a normal distribution in the way a conventional two-sample t-test does. Its interpretation is not simply a test of whether two medians differ: it uses the ranks of the observations, so distributional shape and spread can matter as well as the central values.
The endpoint is reported as medians and inter-quartile ranges, which is a natural descriptive summary when a distribution may be skewed or when a rank-based comparison is used. The registry does not report the individual observations, distribution plots in numerical detail, test statistic, or any model beyond the named method. It is therefore not possible from the registry record alone to evaluate the shape of the outcome distributions or reproduce the test.
What does the p-value convey?
In general, a p-value describes how incompatible the observed data are with a specified null hypothesis, under the assumptions of the statistical test. It is not the probability that the null hypothesis is true, and it does not measure the probability that the observed pattern arose by chance in a literal sense. The reported p = 0.01 is tied to the Wilcoxon (Mann-Whitney) analysis, but the registry does not give the full hypothesis specification or test statistic. The p-value should not be treated as an estimate of the amount of difference between groups.
The label NON INFERIORITY identifies the analysis type, but the record does not give the non-inferiority margin. In general, a non-inferiority analysis asks whether an intervention is not worse than a comparator by more than a prespecified acceptable amount. That margin is central to the interpretation: a p-value without the margin, test direction, and relevant effect estimate cannot establish whether the criterion was met. Those details are not reported in the registry record.
How should medians and inter-quartile ranges be read?
In general, a median is the middle value after observations are ordered. The inter-quartile range gives the interval from the 25th percentile to the 75th percentile, describing the middle half of the observed values. For the SPK group, the median was 30.0 ng/mL and the inter-quartile range was 25.8 to 37.0. For the Oral Supplement group, the median was 25.5 ng/mL and the inter-quartile range was 21.0 to 29.8. These summaries describe each group separately. They do not provide a confidence interval for a between-group effect.
In general, a confidence interval expresses uncertainty around an estimated quantity under a specified method. The registry does not report a confidence interval for the comparison. Without one, the precision of a group contrast cannot be assessed directly from the reported medians and inter-quartile ranges. Overlap or non-overlap of inter-quartile ranges is not a substitute for a confidence interval or a formal comparison.
What is the role of randomization and masking?
The registry records randomized allocation, a parallel design, and triple masking. In general, randomization aims to balance prognostic factors between groups on average and supports causal comparison when allocation and follow-up are implemented appropriately. Masking can reduce bias in care, measurement, and assessment when those involved do not know assignment. The registry does not describe the randomization sequence, concealment process, who was masked, or how masking was maintained. Those details are not reported in the registry record, so the labels alone do not permit an assessment of implementation.
The interventions differ visibly: one involves a kiosk and the other daily pills. The record does not explain how triple masking was maintained across these approaches. It would be inappropriate to infer the success or failure of masking from the label alone.
How do missing outcomes affect interpretation?
In general, missing outcome data can affect a comparison if the likelihood of missingness is related to group assignment or to the outcome itself. The primary outcome description reports 10 subjects of 98 enrolled dropping out before study end and gives final group counts of 43 and 45. The record does not specify which participants dropped out from each group, the reasons, whether outcomes were collected after discontinuation, or the analysis method for missing values. It also does not identify the analysis population by a named principle such as intention-to-treat or per-protocol.
The registry includes planning assumptions for a sample-size illustration based on an observed effect, a two-sided significance level of 0.05, equal allocation, and a normal approximation. Such planning illustrations are not observed power and do not describe the trial’s original design justification. No sample-size justification, target power, or original effect assumption is reported in the registry record. The planning assumptions do not resolve the uncertainty around the posted analysis or missing data.
10. Analyses Reported by the Sponsor
| Method | Estimate | 95% CI | P-value |
|---|---|---|---|
| Wilcoxon (Mann-Whitney) | not reported | 0.010 |
The registry’s posted two-arm analysis is a Wilcoxon (Mann-Whitney) test, with p = 0.01, and is labeled as non-inferiority. It does not report an effect estimate, confidence interval, test statistic, or non-inferiority margin. A separate recalculated comparison is not reported in the registry record, so there is no recalculated estimate or p-value to contrast with the registry’s result.
The posted group summaries are medians and inter-quartile ranges, rather than the individual-level observations needed to reproduce the rank-based test exactly. General re-calculations from summary statistics, when available, are unadjusted and may not match an analysis using participant-level data or a different model. In this record, no disagreement between a sponsor analysis and a recalculation is identified. The reported p-value should be attributed to the registry’s stated analysis, not treated as an independently reproduced result.
The non-inferiority label alone does not supply the missing margin or establish the test’s interpretation. The sponsor’s statistical plan and the full reasoning behind the analysis are not reported in the registry record. The p-value can therefore be described as the posted result, but its relationship to a prespecified non-inferiority criterion cannot be fully assessed from the available record.
11. Multiplicity, Missing Data and Analysis Populations
The registry lists one reported two-arm analysis for the primary serum vitamin D outcome, and two secondary outcomes: device acceptability using the Device Usability Scale and the number of subjects retained at 14 weeks. It also lists five outcome measures overall. The registry record does not report results for those secondary outcomes in the registry record for this analysis. It is not possible to determine whether additional analyses were conducted or whether only selected results were posted.
Multiplicity arises when several outcomes, time points, subgroups, or statistical tests are examined. In general, multiple opportunities to find a statistically notable result can increase the chance of at least one such result even if no real effect exists. Statistical plans may address this through prespecification or adjustment, but whether such procedures were used is not reported in the registry record. No hierarchy of outcomes, multiplicity adjustment, or complete list of planned analyses is described.
The endpoint description reports 10 subjects of 98 enrolled dropping out before study end. The primary outcome summaries include 43 participants in the SPK group and 45 in the Oral Supplement group. The record does not describe reasons for dropout, missingness by group, imputation, sensitivity analyses, or whether the final analysis followed an intention-to-treat or per-protocol approach. Those omissions limit assessment of attrition bias and of the robustness of the result to missing outcomes.
The registry’s total enrollment is 106, while the primary outcome description refers to 98 enrolled subjects. The record does not explain this difference. It also does not report whether the analysis population was defined before the outcome data were reviewed. These are not grounds to assume that the analysis was inappropriate; they are unresolved reporting gaps that affect how confidently the result can be interpreted.
12. 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 |
|---|---|---|---|
| Standing Phototherapy Kiosk (SPK) | 0 | 53 | 0.0% |
| Oral Supplement | 0 | 53 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Standing Phototherapy Kiosk (SPK) | 0 of 53 |
| Oral Supplement | 0 of 53 |
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 |
|---|---|
| Standing Phototherapy Kiosk (SPK) | 0 of 53 |
| Oral Supplement | 0 of 53 |
The registry reports zero serious adverse events in each group among 53 participants at risk per group. It also reports zero other adverse events among 53 participants at risk per group, and zero deaths in each group. No serious adverse event terms are listed.
These figures mean that no events in the reported categories were recorded for the stated at-risk groups during the registry’s safety reporting. They do not establish that the interventions are free of risk. In general, a trial’s ability to characterize uncommon events depends on the number of participants observed, duration of follow-up, event definitions, and completeness of reporting. The record does not provide detailed safety definitions, event collection procedures, or the length of safety follow-up.
The safety denominators are 53 per group, whereas the primary endpoint summaries include 43 SPK participants and 45 Oral Supplement participants. The registry does not explain the difference between these safety and efficacy populations. The reported zero counts should therefore be read as safety results for the stated at-risk groups, not as evidence that every participant included in the trial had complete safety follow-up.
13. What the Result Does, and Does Not, Mean
The posted data describe serum 25 Hydroxyvitamin D levels after 10 weeks in the final SPK and Oral Supplement groups. The SPK group’s median was 30.0 ng/mL, with an inter-quartile range of 25.8 to 37.0. The Oral Supplement group’s median was 25.5 ng/mL, with an inter-quartile range of 21.0 to 29.8. The registry reports a Wilcoxon (Mann-Whitney) p-value of 0.01 and labels the analysis as non-inferiority.
These findings do not, by themselves, show how large or precise the between-group effect is. The median and inter-quartile range are descriptive summaries, and the registry does not report a confidence interval for the contrast. The p-value is not a measure of clinical importance. The non-inferiority margin, hypothesis direction, and effect estimate needed to evaluate the non-inferiority interpretation are not reported in the registry record.
The outcome is a blood measurement at the end of a 10-week intervention. It does not establish effects on symptoms, health outcomes, or longer-term vitamin D status. The trial is described as a pilot feasibility study, and the registry also lists device acceptability and retention as secondary outcomes. Results for those outcomes are not reported in the available record.
It is also not possible to know from the record how missing outcomes were handled or whether the final groups remain comparable after dropout. The result should be understood as a comparison of the observed final outcome groups, with uncertainty about attrition and analysis-population details. It should not be generalized automatically beyond the studied participants, interventions, and follow-up period.
14. Why This Trial Matters Statistically
This trial is statistically notable because the primary outcome is summarized with medians and inter-quartile ranges and analyzed using a rank-based test. That combination makes it important to distinguish descriptions of group distributions from estimates of the treatment contrast. The observed summaries convey central tendency and within-group spread, while the p-value gives a test result; neither alone gives the uncertainty or magnitude of a between-group effect.
The registry also labels the comparison as non-inferiority. This highlights a general reporting principle: a non-inferiority conclusion depends on a clearly stated margin and a defined analysis, not just a p-value. Because the margin and effect estimate are not reported in the registry record, readers cannot independently judge whether the stated statistical criterion was satisfied.
Attrition and analysis populations matter as well. The endpoint description gives final group counts and reports dropouts, while the safety record uses different group denominators. Without group-specific missingness and analysis details, interpretation must account for uncertainty about who contributed to each result. This is especially relevant in a pilot feasibility study, where retention and acceptability are among the listed secondary outcomes.
Finally, the comparison involves distinct delivery methods and a biological endpoint measured at a single stated follow-up time. The findings are therefore best read as a specific short-term comparison, not as a general statement about longer-term outcomes. The record illustrates how descriptive summaries, inferential tests, endpoint choice, missing data, and reporting of a non-inferiority margin all contribute to the statistical meaning of a clinical trial result.
15. 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 registry record does not report the non-inferiority margin, the formal hypothesis direction, a confidence interval for the comparison, or a test statistic. These omissions prevent a full appraisal of what the label NON INFERIORITY means for the reported p = 0.01. The group medians and inter-quartile ranges cannot replace those missing inferential details.
The primary outcome description reports 10 dropouts among 98 enrolled subjects and lists final outcome groups of 43 and 45. Total enrollment is listed elsewhere as 106. The relationship among these counts is not explained in the registry record. Reasons for dropout, missingness by group, and the handling of missing endpoint values are also not reported. The record does not name the analysis population or describe sensitivity analyses.
There are gaps in the design description. Randomized allocation and triple masking are recorded, but the process of sequence generation, allocation concealment, and masking implementation is not reported in the registry record. The interventions are distinct in form, and the record does not explain how masking was maintained. The SPK treatment duration is described differently in the brief summary and arm description.
The primary outcome is a 10-week blood measurement. The record does not provide a baseline-adjusted comparison or say whether the posted analysis used change from baseline. It does not report results for the listed secondary outcomes in the information. Safety definitions, collection procedures, and follow-up details are also not reported. These limitations leave uncertainty about precision, missing data, and the scope of conclusions that can be drawn from the posted result.
16. Related Tutorials
17. Related Statistical Calculators
18. Sources
- ClinicalTrials.gov: Comparing a Novel Phototherapy Kiosk to Oral Vitamin D Supplementation — NCT04556136.
- Registry record last updated 2024-03-13; status last verified 2024-03.
- Results first posted 2024-03-12.
- 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.
Continue through the Clinical Biostats statistical pathway
Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
19. Record Summary
NCT04556136 is a completed randomized, parallel-group trial with triple masking recorded in the registry. It compared a standing phototherapy kiosk with daily oral vitamin D3 supplementation over 10 weeks. The primary endpoint was serum 25 Hydroxyvitamin D level in ng/mL.
The final primary outcome groups included 43 SPK participants and 45 Oral Supplement participants. Their reported medians were 30.0 and 25.5 ng/mL, respectively, with inter-quartile ranges of 25.8 to 37.0 and 21.0 to 29.8. The registry reports a Wilcoxon (Mann-Whitney) p-value of 0.01 and labels the analysis as non-inferiority. The non-inferiority margin and confidence interval are not reported in the registry record.
The endpoint description reports 10 dropouts among 98 enrolled subjects, while the registry lists total enrollment as 106. No explanation of this difference or details on missing-data handling are reported. The registry lists device acceptability and 14-week retention as secondary outcomes. It reports zero serious adverse events, zero other adverse events, and zero deaths in both groups among 53 participants at risk per group.