Special Investigation in Patients With Psoriasis Vulgaris and Psoriatic Arthritis (All Patients Investigation): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Special Investigation in Patients With Psoriasis Vulgaris and Psoriatic Arthritis (All Patients Investigation) (NCT01155570), a registered phase not stated study. The primary outcome is Percentage of Participants With Psoriasis Area and Severity Index 75 (PASI75) Response at Week 16.

2. Clinical Question

3. Trial Design

This is a completed special investigation titled “Special Investigation in Patients With Psoriasis Vulgaris and Psoriatic Arthritis (All Patients Investigation).” The official title describes it as an all-cases investigation in patients with psoriasis vulgaris and psoriatic arthritis. The record lists an enrollment of 752 and identifies AbbVie (prior sponsor, Abbott) as the sponsor. The listed study dates are a start in 2010-02 and primary completion in 2012-07; the status is COMPLETED.

The treatment described is Humira 40 mg (marketed product) every other week by subcutaneous injection after an initial dosage of 80 mg. Allocation is not stated. The record does not describe a like-for-like control arm, so the treatment description should not be read as evidence of a randomized comparison. The registry record also does not report details of recruitment, follow-up procedures, or the extent to which treatment or assessments were standardized.

The primary endpoint is the percentage of participants with a PASI75 response at Week 16, assessed from baseline and Week 16 scores. A secondary outcome listed is the Physician's Overall Response Rating At Week 24. The record lists 23 outcome measures and 17 analyses, but those counts alone do not establish how outcomes were prioritized or how the analyses were organized.

The investigation’s stated aims include describing unknown adverse drug reactions, adverse reactions in clinical use, and factors that may affect safety and effectiveness. Those aims frame the record as a treatment investigation with an emphasis on clinical-setting observations. The registry record does not report a randomized allocation procedure, a protocol-specific comparison, or a statistical analysis plan.

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: Of the 752 participants registered, 4 participants did not have case report forms retrieved (2 whose registration was duplicated and 2 who did not receive Humira). Of the remaining 748 participants, 14 were excluded from analysis (7 changed hospital after registration, 7 didn't visit clinic after the first Humira administration).

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Safety Analysis Population

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: Safety Analysis Population

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Participants With Psoriasis Area and Severity Index 75 (PASI75) Response at Week 16, measured over Baseline and Week 16.

The primary endpoint is the percentage of participants with a PASI75 response at Week 16. PASI75 is defined as at least a 75% reduction in the Psoriasis Area and Severity Index (PASI) score compared with the baseline score. The endpoint is based on the change from baseline to Week 16; the registry describes the percent decrease as the baseline score minus the Week 16 score, divided by the baseline score.

PASI is a disease-severity measure with scores ranging from 0 (best) to 72 (worst), with the highest score representing complete erythroderma of the severest degree. A threshold endpoint such as PASI75 translates change on a score scale into a responder category: participants either meet the defined reduction threshold or do not. Reporting the percentage meeting that threshold can make the result easier to interpret as the frequency of a specified level of improvement in the study population. This is a general explanation of the endpoint type, not a claim about the result.

The registry record specifies the observed-cases population: participants in the Efficacy Analysis Population with an assessment at the time point. It does not report the primary response percentage, a confidence interval, or a test result. Thus, the endpoint definition and assessment time are available, but the registry record does not give the primary estimate needed to judge its magnitude or precision.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a percentage endpoint represent? The primary outcome is a binary responder measure: each assessed participant is classified according to whether the PASI75 threshold is met. The reported quantity would be the percentage of participants meeting that definition in the stated analysis population. In general, a percentage is a way to express the frequency of an event or category within a defined denominator. Its interpretation depends on knowing both the numerator and the population used as the denominator. The registry record gives the endpoint definition and says the analysis uses observed cases in the Efficacy Analysis Population with an assessment at the time point, but it does not report the response percentage or the size of that endpoint population.

Why use a threshold response? PASI75 classifies participants according to whether their score reduction reaches at least the specified threshold. This can be readily understood as a responder frequency. As a general statistical point, converting a continuous score change into a yes-or-no category discards information about how far each participant is above or below the threshold. It can also make results sensitive to the chosen cutoff. The registry record gives the PASI75 definition and the PASI scale, but does not provide the underlying individual score changes or a separate continuous-score result in the registry record for this record.

What does observed cases mean? The stated population includes participants in the Efficacy Analysis Population with an assessment at the relevant time point. In general, an observed-cases analysis uses data available for participants who have the required measurement, rather than assigning a response to every participant who entered the investigation. Such an analysis describes those with observed assessments, and its interpretation may depend on why other assessments are absent. The registry record does not report the number missing, reasons for missing assessments, or a method for handling missing outcomes. It is therefore not possible to assess the effect of missing data on the primary estimate.

What can a confidence interval tell readers? In general, a confidence interval describes statistical uncertainty around an estimate under the assumptions of the method used. A narrower interval indicates greater precision, while a wider interval indicates less precision; it does not by itself resolve design limitations or establish causation. The primary confidence interval is not reported in the registry record. No precision judgment about the Week 16 response estimate can therefore be made from the reported endpoint definition alone.

How should hypothesis tests be interpreted? A p-value, when reported, summarizes how compatible the observed data are with a specified statistical null model under the test’s assumptions. It does not measure the size or clinical importance of an effect, and it is not the probability that the null hypothesis is true. No p-value or primary test result is reported in the record details. The registry record also does not report the statistical test used for the primary outcome, whether it was adjusted, or a prespecified decision threshold.

What is the role of the planning illustration? The sample-size assumptions describe a planning illustration computed from the observed effect, not the investigation’s own design. The stated assumptions are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is expressed as a stated fraction of the observed effect. In general, such an illustration asks how many participants per arm a hypothetical future comparison might require under its assumptions. It is not evidence that the current investigation was designed to that target, and it is not observed power. The record does not report a protocol-based sample-size justification. For time-to-event illustrations, the described quantity is total events; for other illustrations, it is participants per arm.

Why does the study design matter? Statistical estimates must be interpreted in light of how participants entered treatment and how comparisons were formed. Random allocation can help make groups comparable in expectation, while non-randomized observations may be influenced by differences between participants or clinical decisions. Here, allocation is not stated and no like-for-like control comparison is described. This means that even if an outcome estimate were available, it would need to be read as a finding within the reported investigation rather than as a randomized estimate of comparative treatment effect. The registry record does not report adjustment methods that would address potential differences between groups.

Why consider over-dispersion? In general, a statistical model may assume that variability follows a particular distribution. Over-dispersion means the observed variation is greater than the model assumes; if not accounted for, uncertainty estimates can be too small and tests can appear more decisive than warranted. This is a general consideration for some count-data analyses, not a reported feature of this investigation. The record details do not identify an over-dispersion model or a count-data analysis for the primary binary endpoint. The endpoint is described as a percentage of participants with an event.

What does multiplicity change? When many outcomes or analyses are examined, the chance of obtaining at least one apparently unusual result can increase if each is tested separately. Methods such as prespecifying a primary endpoint or adjusting tests can address particular multiplicity concerns, but their choice depends on the analysis plan. The registry lists 23 outcome measures and 17 analyses. It does not report a multiplicity procedure or enough detail to determine how the results were selected, tested, or interpreted together. Counts alone do not indicate whether or how adjustment was needed.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Humira (All Participants)", "Humira (Adalimumab-naive Participants)")
n      <- c(522, 463)
events <- c(257, 245)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Humira (All Participants)  522  257  49.2  44.9  53.6  45.0  53.5  45.0  53.5
ARM  Humira (Adalimumab-naive Participants)  463  245  52.9  48.3  57.5  48.4  57.4  48.4  57.4

11. Multiplicity, Missing Data and Analysis Populations

The record identifies a primary endpoint at Week 16 and a secondary outcome, Physician's Overall Response Rating At Week 24. It also lists 23 outcome measures and 17 analyses. These details indicate that the registry includes multiple outcome and analysis entries, but they do not reveal how those entries were prioritized, whether all were prespecified, or how testing across outcomes was handled. A multiplicity adjustment or other strategy is not reported in the registry record.

Multiplicity matters because interpreting many separate tests can increase the chance that at least one result appears notable by chance. In general, a prespecified hierarchy or adjustment can help control a chosen error rate, but the appropriate approach depends on the trial question and analysis plan. The listed number of outcomes and analyses is not enough to determine which method, if any, was used. The record does not report whether analyses were exploratory or confirmatory.

The primary endpoint is described for observed cases in the Efficacy Analysis Population with an assessment at the time point. That definition makes the availability of a Week 16 assessment relevant to inclusion in the endpoint analysis. The registry record does not report how many participants had an assessment, how many lacked one, why any assessment was missing, or what method was used to address missing data. It also does not report sensitivity analyses for missing outcomes.

The safety figures use a stated at-risk denominator, whereas the primary endpoint population is described by analysis-population membership and assessment availability. The record does not state that these populations are the same. Accordingly, the safety denominator should not be used as a substitute for the primary endpoint denominator. The absence of reported missing-data and multiplicity methods limits assessment of the robustness and interpretability of any unreported efficacy findings.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: pustular psoriasis (0.4%), herpes zoster (0.3%), cholelithiasis (0.3%), pyrexia (0.3%), diverticulitis (0.1%).

The registry record reports 35 participants with serious adverse events among 734 at risk in the Humira group. In the other adverse-event category, it reports 0 affected among 734 at risk. These figures describe recorded safety events and the stated at-risk denominators; they are not a comparison against a control group. The record does not provide a like-for-like control comparison or a causal assessment of individual events.

The serious-event terms listed with percentages are Pustular psoriasis, 0.4%; Herpes zoster, 0.3%; Cholelithiasis, 0.3%; Pyrexia, 0.3%; Diverticulitis, 0.1%; and Encephalitis herpes, 0.1%. The registry record does not give additional details about event timing, severity beyond the serious-event classification, or how investigators assessed relationship to treatment.

As a general principle, safety counts describe events observed and recorded under the investigation’s definitions and follow-up. They do not, on their own, establish that treatment caused an event or that an event could not occur when none was recorded in a category. The listed safety denominator is distinct from the enrollment figure and from the endpoint population description; the record does not state that these populations are identical.

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

The registry record establishes the question the investigation set out to examine: PASI75 response at Week 16 in participants receiving the listed Humira regimen, together with safety observations in clinical use. It defines PASI75 as at least a 75% reduction in PASI from baseline and describes the observed-cases population for the primary endpoint. It also reports the treatment regimen, study status, and safety counts.

However, the primary response percentage is not reported in the registry record. Without that estimate, the magnitude of the Week 16 response cannot be described. The primary confidence interval and test result are also not reported, so its statistical precision and inferential evidence cannot be assessed from these details. A defined endpoint should not be mistaken for a reported outcome.

The record does not describe a randomized control comparison, and allocation is not stated. As a general statistical principle, observations among treated participants do not by themselves isolate the effect of treatment from other influences. The information therefore does not support a comparative claim about Humira versus another treatment or control condition. Nor does the sample-size planning illustration establish that the investigation had a particular design target or achieved a particular power.

The safety counts and listed serious-event percentages are descriptive observations. They do not establish causation or comparative risk. The record does not report the event-assessment details needed to determine whether specific events were attributed to treatment, or how the observation period was handled.

The registry describes an investigation with a defined primary endpoint, a Week 24 secondary outcome, and safety aims. Its reported information is useful for understanding the intended measurement and recorded safety observations, but the absence of the primary result, precision estimates, missing-data details, and a control comparison places substantial limits on conclusions about efficacy or comparative safety.

14. Why This Trial Matters Statistically

This investigation illustrates why a clearly defined endpoint and a reported result are different things. The registry specifies PASI75 at Week 16, including the threshold definition and the baseline comparison. That makes the intended measurement understandable. Yet the primary response percentage and its uncertainty are not reported in the record details, so readers cannot judge the size or precision of the primary finding. Statistical interpretation depends on estimates as well as endpoint definitions.

It also highlights the importance of design when reading clinical outcomes. The record describes a Humira regimen, but allocation is not stated and a like-for-like control comparison is not described. As a general principle, a treatment-group observation is not equivalent to a randomized contrast. That distinction determines what the analysis can establish, regardless of how an endpoint is measured.

The safety information shows another important statistical distinction: a reported event count and its denominator are essential context, but they do not establish causality. The serious adverse event count is reported among participants at risk, and specific event terms are listed with percentages. Without a comparator and further event-assessment information, these observations should be interpreted descriptively.

Finally, the record lists multiple outcomes and analyses, while not reporting a multiplicity strategy or details about missing assessments. These omissions matter because outcome selection, missing data, and repeated testing can affect how trustworthy and interpretable results are. The investigation is therefore a useful case for distinguishing what a registry record documents—design description, endpoint definition, and safety observations—from what requires additional results and analysis details.

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 primary endpoint result is not reported in the registry record details. The response percentage, confidence interval, and test result are absent, preventing assessment of the magnitude, precision, or statistical evidence of the Week 16 finding. The primary population is described as observed cases in the Efficacy Analysis Population with an assessment at the time point, but its size is not reported.

Allocation is not stated, and the record does not describe a like-for-like control comparison. This limits comparative interpretation. The registry record also does not report a protocol-specific sample-size justification, the statistical analysis plan, or the methods used for the primary analysis. The sample-size assumptions are described as a planning illustration based on the observed effect, not the investigation’s own design.

Missing-data details are not reported: the record does not state the number or reasons for missing Week 16 assessments, the handling method, or whether sensitivity analyses were conducted. Although 23 outcome measures and 17 analyses are listed, a multiplicity strategy and the status of individual analyses are not reported.

For safety, the record reports serious adverse event counts and selected serious-event terms with percentages, but additional details on timing, follow-up, and attribution are not reported. The registry record also does not explain how the safety at-risk population relates to the endpoint population. These limitations restrict interpretation of both the efficacy and safety information.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Special Investigation in Patients With Psoriasis Vulgaris and Psoriatic Arthritis (All Patients Investigation) — NCT01155570.
• Registry record last updated 2013-10-08; status last verified 2013-09.
• Results first posted 2013-10-08.
• 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.

19. Record Summary

The record describes a completed special investigation in patients with psoriasis vulgaris and psoriatic arthritis, with psoriasis listed as the condition. It reports enrollment of 752, a start in 2010-02, primary completion in 2012-07, and sponsor AbbVie (prior sponsor, Abbott). The listed Humira regimen is 40 mg every other week by subcutaneous injection after an initial dosage of 80 mg.

The primary endpoint is PASI75 response at Week 16, defined as at least a 75% reduction in PASI from baseline. The analysis population is described as observed cases in the Efficacy Analysis Population with an assessment at the time point. The primary response estimate is not reported in the registry record. A Week 24 Physician's Overall Response Rating is listed as a secondary outcome.

Safety reporting includes 35 participants with serious adverse events among 734 at risk and 0 affected in the other adverse-event category among 734 at risk. Allocation is not stated, and no like-for-like control comparison is described. The record lists 23 outcome measures and 17 analyses but does not report multiplicity or missing-data methods.