Special Investigation in Patients With Psoriatic Arthritis (PsA) (Working Productivity and Activity Impairment [WPAI]): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Special Investigation in Patients With Psoriatic Arthritis (PsA) (Working Productivity and Activity Impairment [WPAI]) (NCT02414633), a registered phase not stated study. The primary outcome is Work Productivity and Activity Impairment Psoriatic Arthritis Questionnaire (WPAI:PsA) Percentage of Overall Work Impairment (OWI): Change From Baseline to Week 24.

2. Clinical Question

The study addresses work impairment associated with psoriatic arthritis among people in paid work who were observed while taking adalimumab in routine clinical practice. Overall work impairment combines absenteeism and presenteeism: missed work and impairment while working. The questionnaire expresses scores as percentages, with 0% representing no impact on productivity and 100% representing complete impact on productivity.

The registry record also lists secondary outcomes concerning other work impairment measures, activity impairment, screening and disease severity measures at specified follow-up weeks. Their presence describes the intended scope of measurement, not the observed results. Without numerical outcome results, the record does not establish the magnitude or precision of change in work impairment.

3. Trial Design

This investigation is described as a special investigation and a post-marketing observational study of adalimumab in Japanese participants with psoriatic arthritis who were engaged in paid work. Participation was non-mandatory. The record identifies one group: participants taking adalimumab under conditions of daily clinical practice. Enrollment was 148.

The record does not describe randomized assignment, and allocation is not stated. No separate control group is listed, so the study is not a randomized comparison and the groups are not a like-for-like control comparison. Observational follow-up can describe measurements collected among participants receiving treatment in practice, but by itself it does not separate treatment-associated change from other influences, such as changes over time or differences between participants.

The study began on 2015-04-01 and primary completion was 2017-03-13. Its status is completed. The primary outcome timeframe is baseline (Week 0) and Week 24. Secondary outcomes include measures scheduled at Weeks 4, 12, 16 and 24, with some outcomes listed for a subset of those weeks. These listed timepoints indicate when outcomes were specified; numerical results for those outcomes are not reported in the registry record.

The primary analysis population is described as all enrolled participants with available overall work impairment scores. The number in that population and how availability was determined are not reported in the registry record. A protocol, detailed sample-size justification, and statistical analysis plan are not reported in the registry record. The record lists 18 outcome measures and 0 analyses. These details limit how fully the design and the intended analysis can be reconstructed from the registry entry.

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

Analysis population for the primary outcome, as defined in the registry: Efficacy analysis population: All enrolled participants with available OWI scores.

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.

6. Primary Endpoint

The registry lists the primary outcome as Work Productivity and Activity Impairment Psoriatic Arthritis Questionnaire (WPAI:PsA) Percentage of Overall Work Impairment (OWI): Change From Baseline to Week 24, measured over Baseline (Week 0), Week 24.

The primary endpoint is the change from baseline to Week 24 in the Work Productivity and Activity Impairment Psoriatic Arthritis Questionnaire percentage of overall work impairment. The measure concerns lost productivity due to psoriatic arthritis in participants engaged in paid work. It is expressed as a percentage: 0% represents no impact on productivity, while 100% represents complete impact on productivity.

Overall work impairment combines absenteeism and presenteeism. Absenteeism represents work missed; presenteeism captures impairment while working. Combining them provides a measure that reflects both forms of work-related impact rather than either alone. The registry record defines overall work impairment as absenteeism plus the non-absenteeism portion multiplied by presenteeism.

The change is defined as the baseline value minus the value at the later timepoint. Under this convention, a negative change represents improvement; the sign should not be read as though it were follow-up minus baseline. The planned summary parameter is a mean, with standard deviation as the dispersion measure.

Using a work-specific measure is relevant to a study focused on participants in paid work because it captures effects on work participation and performance. However, the registry record does not report the baseline or Week 24 mean, the mean change, its standard deviation, or an interval estimate. The endpoint definition therefore clarifies what was intended to be measured, but does not reveal the observed result.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Outcome scale and direction. The primary measure is continuous and expressed as a percentage of overall work impairment. Its endpoints have stated meanings: 0% corresponds to no impact on productivity and 100% to complete impact on productivity. The registry record defines overall work impairment from absenteeism and presenteeism and specifies that change is baseline minus the later value. Therefore, negative change is defined as improvement. This sign convention is specific to the stated calculation; it should not be replaced with the more familiar follow-up-minus-baseline convention.

Mean and standard deviation. The planned parameter is the mean, which describes the average score or average change in the analysis population. A mean can be useful for a continuous outcome, but it does not describe how individual participants' values are distributed. The standard deviation describes spread among observed values around the mean. It is not the same as the uncertainty in the estimated mean. The registry record lists these summary types but does not report numerical primary outcome summaries.

General: uncertainty and confidence intervals. A confidence interval is a statistical way to express uncertainty around an estimated quantity. Its width reflects both the variability in the observations and the amount of information available for the estimate. A narrow interval indicates greater precision than a wide interval, under the assumptions used to construct it. No confidence interval for the primary outcome is reported in the registry record, so its precision cannot be assessed from the record.

General: within-group change and comparison. A baseline-to-follow-up change describes how measured values differ over time among participants included in the analysis. In a study with one listed group, this is not the same as a contrast against a separate control group. Without a comparator, observed change cannot isolate the contribution of treatment from other possible explanations for change. This is a design consideration, not a claim about the direction or size of any unreported outcome.

Observation and allocation. The study is identified as a post-marketing observational investigation in daily clinical practice, and the record lists a single adalimumab group. Allocation is not stated. Random assignment, a control group, and a like-for-like comparison are not described. Consequently, a treatment-versus-control effect estimate is not available from the design details in the registry record.

Analysis population. The primary outcome population is defined as all enrolled participants with available overall work impairment scores. This wording makes score availability part of the stated population definition. It does not say how many participants had scores at baseline and Week 24, whether every available observation was used, or how records with missing follow-up were handled. Those details are not reported in the registry record.

General: missing observations. Missing data can reduce the information available for an estimate and can affect interpretation if the likelihood of having a measurement is related to a participant's outcome or characteristics. Methods such as complete-case analysis or imputation make different assumptions; neither approach is identified in the registry record. It would be inappropriate to infer which method was used or to assume that missing observations had no effect.

Multiple outcomes and timepoints. The registry lists 18 outcome measures, including a primary outcome and secondary outcomes with multiple scheduled follow-up weeks. When many outcomes or timepoints are tested, the chance of at least one seemingly notable result can increase if results are interpreted without accounting for multiplicity. The record does not report a multiplicity adjustment or a detailed statistical plan. Since it also lists 0 analyses, there are no reported analysis details from which to assess how multiple outcomes were handled.

Planning illustration. The sample-size illustration is described as based on the observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; its target effect is a stated fraction of the observed effect. It is a planning illustration, not a description of this investigation's design and not observed power. The investigation lists one group and is not a randomized comparison. A sample-size illustration cannot supply missing outcome estimates or establish the precision of the study's actual results.

General: power and sample size. Power is a design-stage probability of detecting a specified effect under a defined statistical model and assumptions. A planning sample size depends on those assumptions, including the effect targeted and the variability expected. A calculation based on a fraction of an observed effect illustrates a hypothetical planning scenario; it does not demonstrate that an existing study had a particular probability of finding a result. The registry record does not report a trial-specific sample-size justification.

In short, the record defines the endpoint, its calculation, its direction, and its intended summary statistics. It does not provide the numerical results or the detailed analysis procedures needed to reproduce or evaluate an inferential analysis. General statistical concepts can explain what those procedures would mean, but they cannot fill in the unreported analysis choices or results.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists 18 outcome measures. The primary outcome is the change in overall work impairment from baseline to Week 24. Listed secondary outcomes include other work-related measures at specified follow-up weeks, the Psoriatic Arthritis Screening and Evaluation Questionnaire, the Psoriasis Area and Severity Index, and disease activity measures. Several are scheduled at more than one follow-up timepoint.

Assessing numerous outcomes or timepoints creates a multiplicity issue: if many statistical tests are performed, the chance of at least one result appearing notable by chance can increase. Analysis plans may address this through prespecified testing order or other adjustments. A multiplicity strategy is not reported in the registry record. The record lists 0 analyses, so it does not provide reported test results or analysis details from which to determine how multiplicity was handled.

The primary outcome population is defined as all enrolled participants with available overall work impairment scores. The number with available scores is not reported in the registry record. The approach to missing measurements, including any imputation, exclusions, or sensitivity analyses, is also not reported in the registry record. The record does not establish whether follow-up scores were complete or whether missingness could affect interpretation.

The record names an efficacy analysis population but does not report other analysis populations or explain how participants were included in analyses. The difference between total enrollment and the number analyzed therefore cannot be assessed. These reporting gaps limit evaluation of both the completeness of the outcome data and the robustness of any analysis.

11. Safety Results

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

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: cellulitis staphylococcal (0.7%), interstitial lung disease (0.7%), lupus nephritis (0.7%), paradoxical drug reaction (0.7%).

The safety figures are reported for the Humira group, with 148 participants at risk for the serious and other adverse event summaries. Serious adverse events affected 4 participants; other adverse events affected 28 participants. The record lists 0 deaths. These are participant counts, not measures of event severity for each person or estimates of risk relative to an untreated group.

The listed serious adverse event terms are cellulitis staphylococcal, interstitial lung disease, lupus nephritis, and paradoxical drug reaction. Each term is reported as 0.7%. The registry record does not provide further detail about event timing, recurrence, causal attribution, or how the terms were selected for listing. A listed term should not be taken as proof that the event was caused by adalimumab.

Because the investigation lists one group and no comparator, these figures describe reported events in the study group; they do not establish a comparative safety difference. The record does not provide a control-group rate or a basis for attributing an event to treatment. Counts also do not convey the uncertainty around an underlying event frequency. The safety figures should therefore be read as descriptive registry counts and listed terms, not as a comparative estimate.

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

The study record documents an observational investigation of adalimumab in Japanese participants with psoriatic arthritis who were engaged in paid work. It identifies overall work impairment at Week 24 as the primary outcome and defines how change is calculated. It also names secondary measures covering work, activity, screening, and disease status. These details show what the investigation set out to measure.

They do not establish the observed change in work impairment. The primary mean, standard deviation, and numerical change are not reported in the registry record, and no confidence interval or p-value is reported. The amount and precision of any change cannot therefore be described. The endpoint's sign convention indicates what negative change would mean, but it does not show that negative change occurred.

The record describes a single observational group and no comparator. For that reason, a change over time cannot be interpreted as a controlled estimate of the effect of adalimumab. Participants were observed in daily clinical practice rather than assigned to a stated comparison group, and the record does not state an allocation method.

The safety entries describe 4 participants affected by serious adverse events, 28 affected by other adverse events, and 0 deaths in the listed group of 148. Four serious adverse event terms are each listed at 0.7%. Those figures are descriptive and do not provide a comparison or establish causation.

More broadly, the record's outcome definitions and enrollment details are not a substitute for numerical results, a detailed analysis plan, or complete reporting of missing data. The findings cannot be characterized as evidence for or against a treatment effect on work productivity based on this registry record alone. It specifies the question and some safety counts, while leaving the primary outcome result and important analysis details unreported.

13. Why This Trial Matters Statistically

This investigation raises a useful statistical question: how should work-related outcomes be described when participants with a chronic condition are observed in everyday clinical practice? The primary endpoint focuses on overall work impairment, combining absenteeism and presenteeism in a percentage measure. Its definition connects the statistical outcome to an interpretable domain: productivity affected by psoriatic arthritis among people in paid work.

The record also illustrates why an outcome definition and a result are not interchangeable. It specifies the scale, its endpoints, the calculation of change, and the direction that represents improvement. Those details are necessary for correct interpretation. Yet without the numerical baseline, follow-up, and change estimates, neither the magnitude nor the precision of the observed outcome can be assessed.

The observational design matters to the statistical interpretation. A single group followed over time can describe measurements among participants with available scores, but it does not provide a concurrent comparison for separating treatment-associated change from other influences. This is an important distinction when registry records are read alongside study objectives: the type of design determines the kinds of conclusions the data can support.

The record further highlights the importance of complete outcome reporting. Multiple outcomes and follow-up weeks are listed, but no analyses are listed, and methods for multiplicity and missing data are not reported. Without these details, a reader cannot determine how the planned outcome set was analyzed or how incomplete observations were handled.

For biostatistical interpretation, the central lesson is to distinguish measurement, design, analysis, and result. This record describes the first two in part, and includes some descriptive safety counts, but it does not report the numerical primary endpoint findings. Recognizing that boundary prevents an outcome definition or study objective from being mistaken for evidence of an observed effect.

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 principal limitation for interpreting the primary endpoint is that its numerical results are not reported in the registry record. Although the endpoint and intended summary measures are defined, the baseline and Week 24 values, mean change, standard deviation, and interval estimates are absent. The extent and precision of any observed change cannot be evaluated.

The investigation lists one observational group and no comparator. It therefore cannot provide a like-for-like comparison between adalimumab and another group from the design information in the record. Allocation is not stated. The record also does not report a detailed protocol, sample-size justification, or statistical analysis plan.

The stated efficacy population includes enrolled participants with available overall work impairment scores, but the number with available scores is not reported. The handling of missing data and the number included at each follow-up are not reported in the registry record. This prevents assessment of completeness and of whether the analyzed population differs from the enrolled population.

The record lists 18 outcome measures, with several outcomes at multiple weeks, but it does not report a multiplicity approach. It lists 0 analyses, leaving no statistical results or analysis details to evaluate. The absence of those details makes it difficult to assess how outcome selection, repeated timepoints, and uncertainty were handled.

Safety information is descriptive for the single listed group. It does not include a comparator, and the record does not establish causal attribution for listed events. The registry entry also does not report further details such as the timing or recurrence of the adverse events. These limits should be kept in mind when interpreting the reported counts and event terms.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Special Investigation in Patients With Psoriatic Arthritis (PsA) (Working Productivity and Activity Impairment [WPAI]) — NCT02414633.
• Registry record last updated 2018-10-16; status last verified 2018-10.
• Results first posted 2018-10-16.
• 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.

18. Record Summary

The registry record describes a completed post-marketing observational investigation of adalimumab in Japanese participants with psoriatic arthritis who were engaged in paid work. Enrollment was 148. The study began on 2015-04-01 and primary completion was 2017-03-13.

The primary outcome is change from baseline to Week 24 in the percentage of overall work impairment measured by the Work Productivity and Activity Impairment Psoriatic Arthritis Questionnaire. Change is defined as baseline minus the later value, with negative change representing improvement. The primary analysis population is enrolled participants with available scores.

The record lists 18 outcome measures and 0 analyses. It does not report numerical results for the primary endpoint, the method for handling missing data, or a multiplicity approach. The safety summary lists 4 participants with serious adverse events, 28 with other adverse events, and 0 deaths in the Humira group of 148 participants at risk.