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 Prevalence of Psoriatic Arthritis in Adults With Psoriasis: An Estimate From Dermatology Practice (NCT01147874), a randomized phase 4 study. The primary outcome is Percentage of Participants With Psoriatic Arthritis (PsA) Based on Physical Examination, Medical History and Laboratory Results.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01147874 |
| Phase | Phase 4 |
| Condition | Psoriasis, Psoriatic Arthritis |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | None (open label) |
| Enrollment | 1013 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Pfizer |
| Results posted | Yes |
2. Clinical Question
Population
Adults with psoriasis seen in dermatology practice. The registry record describes a full analysis set that included randomized participants who answered a question at the dermatology visit about a previous diagnosis of psoriatic arthritis by a rheumatologist and who had a rheumatologist assessment during the study. The remaining eligibility wording is incomplete in the registry record.
Intervention
This was a non-therapeutic assessment study, not a trial of a treatment intended to change psoriasis or psoriatic arthritis. Participants were evaluated by a dermatologist at Visit 1 and a rheumatologist at Visit 2. A subset proceeded to imaging at Visit 3, including x-ray, MRI, and ultrasound. The listed procedure was lab draws and imaging.
Comparator
No clinical comparator is described for the primary prevalence question. Although the registry labels the study randomized and parallel, it does not describe two comparative treatment groups for the primary endpoint. Its analysis note says the primary outcome has fewer than two arms. The purpose is to estimate the frequency of a diagnosis, rather than to compare treatment effects.
Primary question
What percentage of the evaluated participants with psoriasis were classified by a rheumatologist as having psoriatic arthritis, using medical history, physical examination, and laboratory results? The endpoint covers Week 0 through Week 8. The registry record gives the endpoint definition and a 95% confidence interval as its dispersion measure, but the primary percentage and interval are not reported in the registry record.
3. Trial Design
The record describes a completed, phase 4, multicenter, randomized, non-therapeutic interventional study titled “Prevalence of Psoriatic Arthritis in Adults With Psoriasis: An Estimate From Dermatology Practice.” Enrollment was 1013. The study began in 2010-08 and had primary completion in 2011-07. The listed conditions were psoriasis and psoriatic arthritis.
The assessment pathway began with a dermatologist visit, followed by a rheumatologist visit. The primary endpoint used rheumatologist classification based on medical history, physical examination, and laboratory results. A subset of participants proceeded to a third visit for imaging procedures: x-ray, MRI, and ultrasound. The listed intervention was lab draws and imaging. These procedures formed part of case assessment; the study is explicitly described as non-therapeutic.
The registry labels allocation as randomized, masking as none, and the model as parallel. Those design labels do not, on their own, establish that the primary prevalence estimate compares randomized groups. The record’s primary-outcome note indicates fewer than two arms for that outcome, and the listed arm description is a psoriatic arthritis questionnaire. A detailed account of randomization procedures, the reason for allocation, or the role of the questionnaire is not reported in the registry record.
The study’s stated time frame for the primary outcome was Week 0 through Week 8. The design is therefore best read as an assessment of diagnostic status during a defined study period, not as a randomized test of a therapeutic effect. The record does not report a protocol-level explanation of how the visit sequence, selection for imaging, or randomization relates to the prevalence estimate.
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 | All Participants |
|---|---|
| STARTED | 1013 |
| COMPLETED | 946 |
| NOT COMPLETED | 67 |
Reasons for not completing this period:
| Reason | All Participants |
|---|---|
| Adverse Event | 5 |
| Investigator's Request | 1 |
| Lost to Follow-up | 25 |
| Other | 5 |
| Protocol Violation | 5 |
| Sponsor's Decision | 2 |
| Withdrawal by Subject | 24 |
Analysis population for the primary outcome, as defined in the registry: Full analysis set (FAS) population included all randomized participants with an answer to the question at Visit 1 (dermatology visit) about previous diagnosis of PsA by a rheumatologist and had an assessment of PsA during the study by a rheumatologist based on medical history, physical examination and laboratory results.
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 | All Participants |
|---|---|---|
| Participants analysed | 1013 | |
| Age Continuous | Years | 49.90 (SD 13.82) |
| Sex: Female, Male: Female | Participants | 404 |
| Sex: Female, Male: Male | Participants | 609 |
6. Primary Endpoint
The registry lists the primary outcome as Percentage of Participants With Psoriatic Arthritis (PsA) Based on Physical Examination, Medical History and Laboratory Results, measured over Week 0 through Week 8.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | 95% Confidence Interval |
| Unit | Percentage of participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint is the percentage of participants classified as having psoriatic arthritis by a rheumatologist. The diagnosis was based on medical history, physical examination, and laboratory results. The registry describes the percentage as the number classified positive divided by the total number evaluated. It identifies the endpoint unit as percentage of participants and the dispersion measure as a 95% confidence interval.
This endpoint is used to estimate how frequently psoriatic arthritis was identified among participants with psoriasis assessed in the study. The combined clinical assessment matters because the endpoint is a classification made from several kinds of evidence, rather than a result from a single laboratory test or questionnaire. The visit sequence also places the rheumatology assessment after the dermatology visit.
The registry identifies the endpoint period as Week 0 through Week 8. It describes the full analysis set as randomized participants who answered the Visit 1 question about a previous rheumatologist diagnosis and had a rheumatologist assessment during the study; the rest of the population wording is incomplete in the registry record. The number classified positive, the number evaluated for this endpoint, the resulting percentage, and its confidence limits are not reported in the registry record. Thus, the endpoint’s definition is available, but its numerical estimate and precision cannot be interpreted from this record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The primary outcome is a prevalence-style estimate: it concerns the share of evaluated participants classified as having psoriatic arthritis during the study assessment. It is not a comparison of treatment outcomes. Although the study is labeled randomized, the available primary-outcome information does not describe a comparative effect between two arms. The record’s note indicates fewer than two arms for the primary outcome.
The registry specifies that the diagnosis used medical history, physical examination, and laboratory results, and that a rheumatologist made the classification. Those details define what the endpoint represents. They do not reveal how many participants were classified positive, how many were evaluated, or what percentage resulted. The primary result and its 95% confidence interval are not reported in the registry record. Without those values, the estimated prevalence and its statistical precision cannot be stated.
A confidence interval is, in general, a way to express uncertainty around an estimate. A narrower interval indicates greater precision under the method used, while a wider interval indicates more uncertainty. The registry identifies a 95% confidence interval as the dispersion measure but does not give its endpoints. It is therefore not possible to describe whether the prevalence estimate was precise or imprecise.
The record lists two secondary outcomes: the percentage with psoriatic arthritis based on physical examination and medical history, and the percentage with undiagnosed psoriatic arthritis. It does not report numerical results for those outcomes either. The distinctions in their definitions could matter when comparing estimates: the primary outcome includes laboratory results, while the first secondary outcome does not; the second focuses on previously undiagnosed cases. The posted record does not provide the underlying counts or analysis details needed to quantify those distinctions.
The safety record lists 0 serious adverse events among 1013 participants at risk, and 7 other adverse events among 1013 at risk. These are descriptive counts in the registry record, not evidence about whether a procedure caused an event. No serious-event terms are listed. A death count is not reported in the registry record. The safety figures do not replace the missing primary endpoint results and do not indicate the prevalence of psoriatic arthritis.
Overall, the record establishes the study’s aim, clinical assessment approach, endpoint definition, enrollment, and some safety counts. It does not provide the main numerical finding required to assess the prevalence estimate. Consequently, no conclusion about the size of that estimate or its uncertainty follows from the posted results.
9. Statistical Methods Explained
The primary outcome is a percentage, so the basic statistical quantity is a proportion: the number of participants meeting the endpoint definition relative to the number evaluated for that endpoint. The registry describes the positive classification as one made by a rheumatologist using medical history, physical examination, and laboratory results. No positive count, evaluated denominator, or calculated percentage is reported in the registry record, so the proportion cannot be interpreted numerically.
What does the confidence interval convey?
In general, a confidence interval expresses sampling uncertainty around an estimated quantity. For a percentage, it gives a range of values compatible with the data and the interval method under its assumptions. It is not a guarantee that the true prevalence lies within a particular range, and it does not address every source of uncertainty, such as how participants entered the study or how consistently the diagnosis was assessed. The registry specifies a 95% confidence interval for the primary endpoint, but its limits are not reported in the registry record.
The percentage is meaningful only with a clear denominator. The primary outcome description refers to participants evaluated by a rheumatologist, while the full analysis set description refers to randomized participants with a response to the previous-diagnosis question at Visit 1 and a rheumatologist assessment during the study. The wording of the population description is incomplete. The endpoint denominator and the exact number included in the analysis are not reported in the registry record. The enrollment of 1013 should not be treated as the endpoint denominator unless the record explicitly makes that connection; it does not.
Why does the case definition matter?
Prevalence estimates depend on how a case is defined and identified. Here, the primary definition combines clinical history, examination, and laboratory results, with the classification made by a rheumatologist. The secondary outcome based on physical examination and medical history has a different stated basis, and the undiagnosed-arthritis outcome addresses a distinct question about prior recognition. These endpoints are related but are not interchangeable. Their estimates could differ because their definitions differ, but numerical comparisons cannot be made because results are not reported in the registry record.
In general, diagnostic assessment can also be affected by who receives each assessment and whether all participants receive the same procedures. The registry says a subset underwent imaging at Visit 3. Imaging is not included in the stated primary case definition, and the selection criteria for that subset are not reported in the registry record. The record also does not describe assessor training, diagnostic thresholds, or procedures for resolving uncertain classifications.
What can be learned from the design labels?
The registry labels allocation as randomized, masking as none, and the model as parallel. These are design descriptors, but they do not provide a complete statistical analysis plan. The primary-outcome note indicates fewer than two arms, so a between-arm estimate for that endpoint is not available in the posted description. The registry does not explain what was randomized or how randomization was related to the prevalence objective. No group-specific primary outcome values or comparative estimates are reported.
In general, randomization is used to support fair comparisons between groups when an intervention effect is the question. It does not automatically make a prevalence estimate representative of a broader population. For prevalence, the selection of participants, the assessment process, and the endpoint denominator are central to interpretation. The registry describes dermatology-practice recruitment in the title and the visit pathway, but further recruitment details are not reported in the registry record.
What can be said about planning calculations?
The record describes a planning illustration based on an observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It says the effect to detect is a stated fraction of the observed effect and that non-time-to-event planning results are expressed as participants per arm. These are planning assumptions, not observed trial outcomes. The numerical planning results are not reported in the registry record. The primary outcome also lacks a two-arm comparison, so those generic planning assumptions should not be read as a design justification for this prevalence analysis.
In general, power is a design concept describing the chance that a study will detect a specified effect under assumed conditions. A planning illustration does not show that an observed result had a particular probability of being correct, and it is not observed power. The registry does not report the trial’s own sample-size justification, the assumed prevalence used for planning, or a protocol-level statistical plan. No recalculated effect or discrepancy is available from the posted primary outcome results.
Why can over-dispersion matter?
In general, over-dispersion occurs when observed variation is greater than a chosen statistical model expects. It can make uncertainty estimates too optimistic if the analysis assumes less variation than is present. It is a consideration for some clustered or count-based data, but the primary endpoint is a percentage and no over-dispersion analysis is described. The registry record does not report a model, a variance adjustment, or a method for the confidence interval. There is therefore no basis to claim that over-dispersion was assessed or affected the reported result.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists three outcome measures in total: the primary percentage based on physical examination, medical history, and laboratory results, plus two secondary outcomes. The secondary outcomes concern psoriatic arthritis based on physical examination and medical history, and undiagnosed psoriatic arthritis. The registry does not report numerical results for these outcomes or list any statistical analyses. A multiplicity adjustment or a prespecified hierarchy for interpreting the outcomes is not reported in the registry record.
When several outcomes are examined, multiplicity can increase the chance of at least one apparently notable result arising by chance. In general, an analysis plan may address this through prespecified priorities or adjustments, but the registry does not state whether either approach was used. No p-values or outcome-specific inferential results are reported, so there is no posted set of significance tests to interpret.
The full analysis set description includes participants with an answer to the previous-diagnosis question at Visit 1 and a rheumatologist assessment during the study. The description is truncated, and the exact number in this analysis set is not reported in the registry record. Missing-data counts, reasons for missingness, exclusions, and methods for handling missing outcome information are not reported. It is therefore unclear how participants without complete assessments were treated.
The record does not state whether the analysis was restricted to the described set, whether any alternative analysis populations were used, or how participants with incomplete or uncertain diagnostic assessments were handled. These details affect the denominator and can influence interpretation of a prevalence estimate. The enrollment figure alone does not establish the number contributing to the endpoint.
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 |
|---|---|---|---|
| All Participants | 0 | 1013 | 0.0% |
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 |
|---|---|
| All Participants | 7 of 1013 |
Most frequent non-serious adverse event terms
| Event term | Organ system | All Participants |
|---|---|---|
| Claustrophobia | Psychiatric disorders | 5 of 1013 |
| Procedural dizziness | Injury, poisoning and procedural complications | 1 of 1013 |
| Dizziness | Nervous system disorders | 1 of 1013 |
The safety record lists 0 serious adverse events among 1013 participants at risk. It also lists 7 other adverse events among 1013 participants at risk. These are counts, and the posted record does not provide further event-level detail for the other adverse events. No serious adverse-event terms are listed. A death count is not reported in the registry record.
These figures describe the safety fields recorded for the study; they should not be read as proof that an event was or was not caused by study procedures. The study is described as non-therapeutic and includes clinical assessments, laboratory draws, and imaging for a subset, but the safety counts do not assign events to a particular procedure. The registry record does not provide timing, severity details for the other events, or a causal assessment.
The all-participant risk group is the denominator stated for these safety counts. It is not necessarily the endpoint analysis population, which is described separately. The counts therefore should not be used to infer the primary prevalence result. They also do not establish the absence of all possible harms; they state only what the safety record lists.
12. What the Result Does, and Does Not, Mean
The study addresses a descriptive clinical question: among adults with psoriasis assessed in dermatology and rheumatology practice, what percentage were classified as having psoriatic arthritis under the study’s diagnostic approach? The registry provides important parts of that question’s definition, including the rheumatologist assessment and the use of medical history, physical examination, and laboratory results. It also describes a Week 0 through Week 8 endpoint period.
The registry record does not report the primary percentage, its numerator or denominator, or the endpoints of its 95% confidence interval. As a result, the size of the estimated prevalence and the precision of that estimate cannot be described. The same absence applies to the two secondary outcome results. The record therefore does not support a numerical statement about how often psoriatic arthritis was identified in this study.
Even if the primary result were available, a prevalence estimate from participants assessed in dermatology practice would describe the study population and its assessment process. It would not automatically establish prevalence in every population of adults with psoriasis. Generalizability depends on who was enrolled, how they were selected, and whether the assessment pathway resembles that in the population of interest. Detailed recruitment and selection information is not reported in the registry record.
The findings also would not, by themselves, establish the effect of treatment. The study is described as non-therapeutic, and the primary outcome is diagnostic classification rather than a treatment comparison. The randomized and parallel labels do not supply a treatment contrast for the prevalence endpoint; the record notes fewer than two arms for that outcome.
The safety counts are separate descriptive information. The record lists 0 serious adverse events and 7 other adverse events among 1013 participants at risk, while a death count is not reported in the registry record. These data do not fill the gap in the primary endpoint result or identify the cause of any event.
13. Why This Trial Matters Statistically
This study illustrates why a registry entry must be read at the level of the estimand: the precise quantity the analysis is intended to describe. The stated primary estimand is a percentage of participants classified as having psoriatic arthritis, using a rheumatologist’s assessment based on clinical history, examination, and laboratory results. It is not a treatment effect, despite the registry’s randomized and parallel design labels.
For a prevalence estimate, the denominator and case definition are essential. Enrollment was 1013, but the primary endpoint refers to participants evaluated, and the full analysis set description requires a Visit 1 response and a rheumatologist assessment. The endpoint-specific denominator is not reported in the registry record. Without it, the registry’s enrollment count cannot be substituted for the analysis denominator.
The record also shows how closely related outcomes can encode different questions. One secondary outcome uses physical examination and medical history, while the primary outcome additionally includes laboratory results. Another secondary outcome focuses on cases that had not previously been diagnosed. Clear definitions are important because differences in estimates could reflect the measurement rules rather than a change in the underlying condition. Numerical results are not reported, so that distinction remains methodological rather than quantitative in this record.
Finally, a stated confidence-interval method is not the same as a reported interval. The record identifies a 95% confidence interval, but without its limits the reader cannot judge precision. This is a useful reminder that endpoint definitions and design descriptions explain what a study intended to measure, while the numerical result is needed to assess what it found.
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 central limitation for interpretation is that the primary percentage and its 95% confidence interval are not reported in the registry record. The underlying positive count and evaluated denominator are also absent. This prevents assessment of both the estimated prevalence and its precision. Numerical results for the secondary outcomes are not reported either.
The full analysis set description is incomplete. It identifies a Visit 1 response about previous diagnosis and a rheumatologist assessment as eligibility features, but the remainder of the population wording is cut off. The exact analysis population size, missing-data handling, exclusions, and reasons for missing assessments are not reported in the registry record. These details are especially important for a percentage endpoint because the denominator determines what population the estimate describes.
The study title refers to dermatology practice, but detailed information about recruitment, site selection, and participant characteristics is not reported. The extent to which the participants represent other adults with psoriasis therefore cannot be evaluated from the registry record. The record also notes that a subset received imaging, but it does not describe how that subset was selected. Imaging is not part of the stated primary diagnostic basis, but different assessment pathways could still affect how results are interpreted.
Although allocation is labeled randomized, the record does not explain what was randomized or how that allocation relates to the prevalence objective. It lists no comparative primary outcome arms and notes fewer than two arms for that outcome. The statistical analysis methods, confidence-interval calculation, diagnostic thresholds, assessor procedures, and any approach to uncertain classifications are not reported in the registry record. These omissions limit assessment of reproducibility and possible sources of measurement variation.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Prevalence of Psoriatic Arthritis in Adults With Psoriasis: An Estimate From Dermatology Practice — NCT01147874.
- Registry record last updated 2012-06-21; status last verified 2012-04.
- Results first posted 2012-06-21.
- 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
This completed phase 4 study enrolled 1013 participants and examined the prevalence of psoriatic arthritis among adults with psoriasis. The registry describes a dermatologist assessment at Visit 1, a rheumatologist assessment at Visit 2, and imaging at Visit 3 for a subset. The primary endpoint was the percentage classified positive by a rheumatologist using medical history, physical examination, and laboratory results, with a stated 95% confidence interval over Week 0 through Week 8.
The primary percentage, confidence limits, endpoint counts, and secondary outcome results are not reported in the registry record. The record lists 0 serious adverse events and 7 other adverse events among 1013 participants at risk; a death count is not reported. The study is labeled randomized, unmasked, and parallel, but the primary outcome description indicates fewer than two arms. The record does not report detailed statistical methods, missing-data handling, or a multiplicity plan.