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 Guselkumab in the Treatment of Pityriasis Rubra Pilaris (PRP) (NCT03975153), a na phase 2 study. The primary outcome is Mean Change From Baseline Psoriasis Area and Severity Index (PASI) at Week-24 After Treatment With Guselkumab..
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT03975153 |
| Phase | Phase 2 |
| Condition | Pityriasis Rubra Pilaris |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 15 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Oregon Health and Science University |
| Results posted | Yes |
2. Clinical Question
Population
Adults with pityriasis rubra pilaris (PRP) were the population named in the trial title and official title. The brief summary describes treatment of patients with PRP. Further eligibility criteria and details about the enrolled participants are not reported in the registry record.
Intervention
The intervention was guselkumab, described as treatment for 20 weeks. The registry identifies it as a biological intervention. Details about dose, administration schedule, and treatment adherence are not reported in the registry record.
Comparator
There was no separate comparator group in this single-group, open-label pilot trial. Allocation is recorded as not applicable, and masking as none. The trial therefore does not provide a randomized, like-for-like comparison with placebo or another treatment.
Primary question
The stated primary question concerns mean change from baseline in the Psoriasis Area and Severity Index (PASI) at week 24 after guselkumab treatment. PASI assesses skin appearance using erythema, scale, and elevation in relation to body surface area. The numerical result for this outcome is not reported in the registry record, so the magnitude and precision of any change cannot be described from this record.
3. Trial Design
This was an open-label pilot trial of guselkumab in adults with PRP. The registry records it as a phase 2, single-group study with no masking and no applicable allocation. Its status is completed, and enrollment is listed as 15. A single-group design describes observations in a treated group; it does not create a concurrent untreated or active-treatment group against which to estimate a comparative effect.
The brief summary describes 20 weeks of guselkumab treatment. It also states that participants were required to travel to Portland, Oregon, for the first visit, the week-4 visit, and the week-24 visit. Three visits between those visits and one follow-up visit could be conducted by secure videoconferencing. The registry lists the study start as 2019-10-03 and primary completion as 2022-08-11.
The primary outcome is mean change from baseline in PASI at week 24. The record also lists quality-of-life improvement measured with the Dermatology Life Quality Index at week 24, and a week-36 outcome concerning participants with >50% improvement in PASI at week 24 who did not worsen at week 36. The number of outcome measures is listed as 3. Details of the third measure are not reported in the registry record.
Because the study is open-label and lacks a control group, its observations can describe outcomes during treatment but cannot isolate a treatment effect from other explanations, such as the course of the condition over time or expectations during an unmasked study. Further design details, including eligibility criteria and treatment dosing, 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.
Overall Study
| Stage | Guselkumab Treatment |
|---|---|
| STARTED | 14 |
| COMPLETED | 12 |
| NOT COMPLETED | 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.
Population: Per-protocol population
| Characteristic | Unit | Guselkumab Treatment |
|---|---|---|
| Participants analysed | 12 | |
| Age, Continuous | years | 56.5 (SD 18.7) |
| Sex: Female, Male: Female | Participants | 4 |
| Sex: Female, Male: Male | Participants | 8 |
| Ethnicity (NIH/OMB): Hispanic or Latino | Participants | 0 |
| Ethnicity (NIH/OMB): Not Hispanic or Latino | Participants | 12 |
| Ethnicity (NIH/OMB): Unknown or Not Reported | Participants | 0 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 0 |
| Race (NIH/OMB): Asian | Participants | 1 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 |
| Race (NIH/OMB): Black or African American | Participants | 0 |
| Race (NIH/OMB): White | Participants | 11 |
| Race (NIH/OMB): More than one race | Participants | 0 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 0 |
| Region of Enrollment: United States | participants | 12 |
| Psoriasis Area and Severity Index | units on a scale | 30.6 (SD 11.4) |
| Dermatology Life Quality Index | units on a scale | 20.1 (SD 6.8) |
| Itch numeric rating scale | units on a scale | 6.9 (SD 2.2) |
6. Primary Endpoint
The registry lists the primary outcome as Mean Change From Baseline Psoriasis Area and Severity Index (PASI) at Week-24 After Treatment With Guselkumab., measured over 24 weeks.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Full Range |
| Unit | percent change from baseline PASI |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is mean change from baseline in the Psoriasis Area and Severity Index (PASI) at week 24 after guselkumab treatment. PASI is a measure of skin disease severity based on erythema, scale, and elevation, considered in relation to body surface area. The registry description states that 0 indicates completely clear skin, 72 is the maximum score indicating the worst severity, and a score of 11 or higher is considered severe disease.
Change from baseline is used to describe how a measurement differs from its starting value over a specified period. A group mean can summarize the average change, while the spread of individual observations helps show how consistently participants' measurements changed. The endpoint is expressed as percent change from baseline PASI, and the listed dispersion is the full range. The numerical mean, range, and other numerical results for this endpoint are not reported in the registry record.
PASI provides a structured way to assess skin signs and affected body surface area. It is not a direct measure of every aspect of PRP or of participants' overall experience. The record also names quality of life as a secondary outcome, but its numerical results are not reported in the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record identifies a primary endpoint and describes the study design, but it does not report the numerical week-24 PASI result. In particular, a mean change, range, confidence interval, and statistical test result are not reported in the registry record. Without those estimates, the size and precision of the observed change cannot be assessed from the record. The outcome title alone does not establish the direction or magnitude of the result.
The trial was single-group and open-label. Any PASI change observed in such a design would describe the treated group over time, rather than the difference between guselkumab and a control group. In general, a before-and-after change can reflect multiple influences, including natural variation over time, concurrent care, measurement variability, and expectations. A concurrent comparator can help address some of these alternative explanations, but this trial did not include one.
The record lists enrollment of 15, while the safety group lists 12 at risk for serious adverse events and 12 at risk for other adverse events. Those are different record entries and should not be treated as interchangeable denominators. The registry does not report the reasons for the difference or the analysis population for the primary endpoint. It also does not report how many participants contributed primary outcome data at week 24.
The secondary outcomes describe a week-24 quality-of-life improvement and a week-36 assessment among participants meeting a PASI improvement criterion at week 24. Their numerical results are not reported in the registry record. The record lists 3 outcome measures but provides descriptions for the primary outcome and two secondary outcomes. It lists 0 analyses. The registry record therefore does not support a numerical account of the estimated effect, uncertainty, or statistical significance for these outcomes.
These limitations are important when reading any displayed analysis. A confidence interval, in general, communicates the range of effect estimates compatible with the data and statistical model at a stated confidence level. It is not a guarantee that the true effect lies in that interval. No confidence interval for the primary endpoint is reported in the registry record. Likewise, a p-value, if reported, would address compatibility with a specified null model; it would not by itself establish clinical importance. No primary endpoint p-value is reported in the registry record.
The registry's planning illustrations are not trial results. The stated assumptions describe a hypothetical two-arm calculation using a two-sided significance level of 0.05, equal allocation, and a normal approximation. The illustration is based on fractions of an observed effect, but the numerical effect and calculated planning values are not reported in the registry record. Such planning values are not observed power and do not substitute for the trial's outcome estimates. Because the actual trial was single-group, the two-arm planning setup is not a description of its design.
9. Statistical Methods Explained
Several statistical ideas help distinguish what a single-group pilot can describe from what it can establish. The registry records a mean change from baseline in PASI at week 24 as the primary outcome. A mean is a measure of the center of a set of observations: it combines participants' changes into an average. That average can be useful, but it may conceal variation. The record lists the full range as the dispersion measure, which describes the smallest and largest values in the set. The actual mean and range are not reported in the registry record.
What does a change from baseline represent?
A change score compares a measurement at follow-up with that participant's starting measurement. In general, using change can make the starting point explicit and focus attention on movement over time. It does not, by itself, show what would have happened over the same period without the intervention. In a single-group study, there is no randomized control group to estimate that counterfactual course. The recorded endpoint is expressed as percent change from baseline PASI, but the method used to calculate individual or group percent change is not reported in the registry record.
Baseline values can also matter when interpreting change. Participants may begin with different levels of severity, and their possible changes can depend on those starting values. The registry description explains the PASI scale but does not report baseline PASI values or their distribution. It also does not describe any adjustment for baseline characteristics. Those details are not reported in the registry record.
How should uncertainty be understood?
In general, an estimate is more informative when accompanied by a measure of uncertainty. A confidence interval gives a range of values compatible with the observed data under the analysis assumptions. Its width reflects both variability and the amount of information available. A narrow interval indicates greater precision than a wide one, but interpretation also depends on the endpoint and study design. No numerical confidence interval for the primary outcome is reported in the registry record.
A p-value is another general statistical summary. It measures how unusual the observed data, or more extreme data, would be under a specified null hypothesis and model. It does not measure the probability that the null hypothesis is true, and it does not indicate whether an effect is important to patients. The record lists 0 analyses, and a primary endpoint p-value is not reported in the registry record. The analysis model, test, and handling of repeated or incomplete measurements are also not reported in the registry record.
Why do single-group results need cautious interpretation?
Without a concurrent comparator, a measured change over time cannot be separated cleanly from other influences. General examples include natural fluctuation in a condition, regression toward a participant's typical measurement after an unusually high or low starting value, changes in other care, and differences in assessment. Open-label conduct can also affect expectations and reporting. These are general design considerations, not findings about what occurred in this trial. The registry record does not report methods intended to quantify or adjust for these influences.
Blinding is one way to reduce the influence of expectations on some assessments. Masking is recorded as none, and the study is described as open label. PASI includes assessed skin features, so an unmasked assessment can be relevant when considering potential measurement bias. The registry does not report assessor training, independent review, or other procedures for standardizing outcome assessment.
What do the planning assumptions mean?
General sample-size planning asks how many observations might be needed to detect an effect of a stated size under specified assumptions. The registry's planning illustration uses a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It describes planning for fractions of the observed effect. The calculated planning values are not reported in the registry record. The assumptions are distinct from the actual single-group design and do not provide evidence that the study had a particular probability of detecting an effect. Sample-size illustrations are planning tools, not observed power.
The assumptions also do not reveal the trial's original design rationale. A sample-size justification, the effect size used in the trial's own planning, and any interim analysis plan are not reported in the registry record. The stated planning illustration should therefore be read as a separate hypothetical calculation, not as a description of the study's prespecified statistical plan.
Why can variation affect an estimate?
In general, high variation among participants makes an average less precise, especially when the amount of outcome information is limited. The range can show the span of observations but is sensitive to extreme values and does not describe the distribution between the endpoints. Other summaries, such as a standard deviation or a confidence interval, answer different questions. The registry lists full range as the dispersion measure; numerical values for the range and other variability summaries are not reported in the registry record.
Outcome distributions can also depart from assumptions used by common statistical methods. For count data, over-dispersion means that variability exceeds what a simple model expects, which can lead to uncertainty estimates that are too small if ignored. That general issue does not establish that over-dispersion occurred: the primary endpoint is a PASI change measure, and the registry does not report a statistical model or diagnostic assessment. The suitable analysis depends on the outcome scale, observed distribution, and study question.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists one primary outcome and two described secondary outcomes: a week-24 Dermatology Life Quality Index improvement outcome and a week-36 outcome about maintaining a PASI improvement criterion. It records 3 outcome measures overall, but the details of the remaining measure are not reported in the registry record. The record lists 0 analyses and does not provide numerical results for the described outcomes.
When a study evaluates several outcomes or makes several statistical tests, the chance of at least one apparently notable result can increase. In general, multiplicity procedures can adjust how results are interpreted or how statistical error is controlled. Whether any such procedure was planned or used is not reported in the registry record. The primary endpoint's analysis plan and any prespecified hierarchy among outcomes are also not reported in the registry record.
Missing-data methods are important when some participants do not contribute measurements at every follow-up. The registry does not report the number with week-24 PASI data, the amount or pattern of missing outcome data, or any imputation or sensitivity analysis. The analysis population for the primary endpoint is not reported in the registry record. It is therefore not possible to determine from the record how incomplete follow-up was handled or how sensitive the results might be to missing observations.
Likewise, methods for protocol deviations, treatment discontinuation, or adherence are not reported in the registry record. These omissions limit assessment of how the analysis population relates to the enrolled group and whether the reported outcome, if available, would reflect all enrolled participants or a subset.
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 |
|---|---|---|---|
| Guselkumab Treatment | 1 | 12 | 8.3% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Guselkumab Treatment | 1 of 12 |
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 |
|---|---|
| Guselkumab Treatment | 8 of 12 |
Most frequent serious adverse event terms
| Event term | Organ system | Guselkumab Treatment |
|---|---|---|
| Cholecystitis leading to myocardial infarction and death | Cardiac disorders | 1 of 12 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Guselkumab Treatment |
|---|---|---|
| Temporary PRP worsening | Skin and subcutaneous tissue disorders | 1 of 12 |
| Ectropion | Eye disorders | 1 of 12 |
| Elevated creatinine | Renal and urinary disorders | 1 of 12 |
| Gastroenteritis | Gastrointestinal disorders | 1 of 12 |
| Weight loss | Metabolism and nutrition disorders | 1 of 12 |
| Ground level fall | Social circumstances | 1 of 12 |
| Injection site reaction | Skin and subcutaneous tissue disorders | 1 of 12 |
| Scalp pustules | Skin and subcutaneous tissue disorders | 1 of 12 |
| Pulmonary nodule | Respiratory, thoracic and mediastinal disorders | 1 of 12 |
| False-positive hyperkalmia | Blood and lymphatic system disorders | 1 of 12 |
Serious events with the highest arm-level rate: cholecystitis leading to myocardial infarction and death (8.3%).
The safety group lists 12 participants at risk for serious adverse events, with 1 affected, and 12 at risk for other adverse events, with 8 affected. The record also lists 1 death. These figures describe the registry's safety entries; they do not establish that guselkumab caused an event. The relationship between an event and treatment, including the attribution method, is not reported in the registry record.
The listed serious adverse event term is “Cholecystitis leading to myocardial infarction and death,” with 8.3% shown for that term. This term describes a serious event involving a sequence of conditions and an outcome. The registry entry does not provide further clinical detail, timing, or an assessment of causality. The death count and the event term should be read as reported safety information, not as evidence by themselves about the cause of the event.
Safety denominators are not the same as the enrollment entry, and the registry does not explain the difference. It also does not report event-level details, the number of events per affected participant, or follow-up duration for safety ascertainment. The counts alone cannot establish comparative risk because there is no control group in this single-group trial.
12. What the Result Does, and Does Not, Mean
The record describes a completed, open-label pilot study of guselkumab in adults with PRP and specifies a week-24 PASI endpoint. It also provides a limited set of safety counts. These details establish the study question and some features of its design, but they do not supply the numerical primary outcome result. The mean change, its range, and its uncertainty are not reported in the registry record.
Consequently, the record does not support a conclusion about the size or precision of a PASI change during treatment. Nor can it establish a comparative effect: the study had one group and no control arm. An observed change in a single group, even when measured consistently, cannot by itself distinguish an intervention-associated change from time trends, natural variation, or other influences.
The secondary outcomes could add information about quality of life and the later course of PASI among participants meeting the stated improvement criterion. Their results are not reported in the registry record. The descriptions of these measures do not indicate whether their criteria were met or how participants' outcomes changed.
The safety entries should be interpreted with similar restraint. The record reports adverse event counts and a serious event term, including a death, but it does not report a comparator group or enough event detail to estimate comparative risk or establish causation. Counts are important descriptive information; they are not, by themselves, proof that a treatment caused or prevented an event.
Overall, the registry record documents a pilot study's design, intended outcome, and selected safety information. It does not provide the numerical efficacy results needed to quantify the primary endpoint, nor does it support a controlled estimate of treatment effect. These are limits on what can be concluded from this record, not evidence that an unreported outcome was favorable or unfavorable.
13. Why This Trial Matters Statistically
Pilot studies can be useful for documenting whether a clinical question has been studied and for describing how a larger or more controlled study might be structured. This record makes the target population, intervention, duration, and week-24 primary outcome explicit. It also identifies secondary outcomes addressing quality of life and a later PASI assessment. Those features help readers understand what the investigators intended to measure.
The statistical value of the study record depends on more than the choice of endpoint. The design determines which comparisons are possible. A single-group, open-label study can describe changes over time in the group, but it cannot estimate a randomized contrast with a control group. Recognizing that distinction prevents a within-group observation from being interpreted as a controlled treatment effect.
Outcome reporting is also central. The registry identifies the primary outcome but does not report its numerical estimate or uncertainty. Without those quantities, readers cannot assess the magnitude, variability, or precision of the primary result. The absence of numerical results for the described secondary outcomes similarly limits interpretation of those measures.
The safety entries illustrate why denominators and event descriptions matter. The record gives separate at-risk counts for serious and other adverse events, along with affected counts, a death count, and a named serious event term. Careful reading keeps these descriptive observations separate from causal attribution or comparative risk claims, neither of which can be derived from the listed counts alone.
For biostatistical interpretation, this trial therefore highlights the importance of aligning the question, design, analysis, and reporting. A defined outcome and a completed status are not substitutes for numerical results, uncertainty estimates, or a comparator when the aim is a comparative effect. The record makes several design features visible while leaving key analysis and result details unreported.
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 the primary endpoint is that its numerical result is not reported in the registry record. The record identifies the measure and time point, but does not give the mean change, range, confidence interval, or statistical test result. A statistical analysis plan and the primary endpoint analysis population are also not reported in the registry record.
The single-group design and absence of masking restrict interpretation. Without a concurrent comparison group, changes over time cannot be attributed uniquely to the intervention. Open-label assessment may also leave room for expectation-related influences. Procedures for outcome assessor training, independent review, or other bias reduction are not reported in the registry record.
Enrollment is listed as 15, while the safety group lists 12 at risk for each adverse-event category. The reasons for this difference and the number contributing week-24 PASI data are not reported in the registry record. Missing-data amounts, handling of incomplete measurements, and sensitivity analyses are not reported either. These gaps make it difficult to assess follow-up completeness and the population represented by an outcome estimate.
The registry describes two secondary outcomes and lists 3 outcome measures overall, but the third measure's description is not reported in the registry record. Numerical secondary outcome results, multiplicity procedures, adherence, treatment discontinuation, and protocol deviations are also not reported. Dose details and fuller eligibility criteria are absent from the registry record.
Safety interpretation is limited by the absence of event-level clinical details and comparative data. The record does not report how treatment relatedness was assessed or provide enough information to determine whether the serious event term and the death count reflect the same participant. These limits do not negate the reported safety entries; they restrict the conclusions that can be drawn from them.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Guselkumab in the Treatment of Pityriasis Rubra Pilaris (PRP) — NCT03975153.
- Registry record last updated 2024-05-24; status last verified 2024-05.
- Results first posted 2024-05-24.
- 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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18. Record Summary
The registry identifies NCT03975153 as a completed phase 2, open-label, single-group pilot trial of guselkumab in adults with pityriasis rubra pilaris. Enrollment is listed as 15. The intervention is described as 20 weeks of treatment, and the primary outcome is mean change from baseline PASI at week 24.
The record lists two secondary outcomes concerning week-24 quality of life and a week-36 PASI assessment. It reports safety counts for serious and other adverse events and lists 1 death. Numerical primary and secondary outcome results, analysis methods, missing-data handling, and the primary analysis population are not reported in the registry record.