Study Evaluating the Cost of the Treatments of the Refractory Psoriatic Arthritis to the Conventional Therapy: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Study Evaluating the Cost of the Treatments of the Refractory Psoriatic Arthritis to the Conventional Therapy (NCT00303186), a registered phase not stated study. The primary outcome is Mean Cost Per Participant Per Month at Month 12.

2. Clinical Question

The study’s stated purpose is to describe the economic burden of refractory psoriatic arthritis care, including the resources absorbed by the disease and its management. Its primary outcomes are described as qualifying that burden. Secondary aims include assessing efficacy, safety, and cost effectiveness across different therapies, but the record does not provide numerical results for those aims.

This is an observational economic evaluation, not a randomized test of treatment assignment. Consequently, a difference in costs between treatment groups, if reported elsewhere, would not by itself establish that treatment choice caused the difference. The record does not report the group definitions, the numerical cost estimates, or an adjusted comparative analysis.

3. Trial Design

The registry record describes an observational study evaluating the cost of treatment for refractory psoriatic arthritis. Its title and stated purpose focus on conventional therapy, biologic therapy, and the direct and indirect costs of disease management. The study is marked completed. The recorded start is 2005-02, and the primary completion is 2011-06. Enrollment is listed as 107.

Because the study is observational, the therapies should not be treated as randomized arms. The registry record does not state how treatment was allocated, whether allocation was based on clinical decisions or other factors, or how the treatment groups were defined. It explicitly cautions that this is not a randomized comparison and that the arms are not a like-for-like control comparison. Those features limit causal interpretation: clinical and other differences between people receiving different therapies could also be related to their costs or outcomes.

The primary endpoint is mean cost per participant per month at Month 12. The cost measure combines direct costs and indirect costs, with productivity losses identified as the indirect component. Direct costs include pharmacological treatment, hospitalizations, diagnostic examinations, laboratory analysis, specialist visits, and transports. The record describes the primary assessment as part of a health economics evaluation intended to quantify the burden of refractory psoriatic arthritis care.

The registry lists 28 outcome measures and 54 analyses. Secondary outcomes include response measures, psoriasis severity, functional and disease activity indices, a radiology index, and physical measurements. The record does not describe the analysis plan, the timing or definitions of the listed analyses beyond the primary endpoint timeframe, or how the secondary outcomes were combined or prioritized. Specific treatment-group results are not reported in the registry record.

The sponsor is Pfizer. The record does not report a randomization procedure, masking, a control-group protocol, or a sample-size justification. These omissions matter when interpreting comparisons: the design description supports reading the work as an observational assessment of costs, rather than as evidence from a randomized head-to-head treatment comparison.

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

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Intent-to-Treat (ITT) population included all participants who received at least 1 dose of the study medication.

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 Mean Cost Per Participant Per Month at Month 12, measured over Month 12.

The primary endpoint is mean cost per participant per month at Month 12, expressed in Euro/participant-month. It is a continuous measure: each participant’s costs are represented on a monetary scale, and the endpoint summarizes those values using a mean. The registry specifies standard deviation as the measure of dispersion.

The cost measure is intended to capture the economic burden of refractory psoriatic arthritis care and treatment. It includes direct costs for pharmacological treatment, hospitalizations, diagnostic examinations, laboratory analysis, specialist visits, and transports. It also includes indirect costs from productivity losses. Combining these categories is intended to express disease management and its resource use in monetary terms.

A mean can be useful for economic planning because it describes average cost across the analyzed population. It can also be influenced by participants with unusually high costs, so the mean should be read alongside a measure of variability and, where available, the distribution of costs. The registry identifies standard deviation as the dispersion measure, but the numerical mean and standard deviation are not reported in the registry record.

The endpoint is defined for the Intent-to-Treat population, which the record describes as all participants who received at least 1 dose of study medication. Enrollment is listed as 107, but the number included in this endpoint analysis is not reported in the registry record. The endpoint definition and timeframe are available; a numerical estimate, confidence interval, and treatment-group breakdown are not reported.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary measure is a continuous outcome: cost on a monetary scale. The registry specifies a mean and standard deviation. In general, a mean describes the average observed value in an analyzed group, while a standard deviation describes how dispersed individual values are around that average. A mean is often useful for summarizing resource use, but it can be pulled by a small number of unusually high-cost observations. The registry record does not report the numerical mean or standard deviation for this endpoint.

What does the mean represent?

The endpoint is defined as cost per participant per month at Month 12, with the unit Euro/participant-month. The cost definition combines direct costs with indirect costs from productivity losses. Direct costs are specified as pharmacological treatment, hospitalizations, diagnostic examinations, laboratory analysis, specialist visits, and transports. This definition gives the endpoint a broad economic interpretation: it aims to represent costs associated with care and disease management, rather than a medication-only measure.

In general, cost data can be unevenly distributed. Many participants may have relatively modest costs while a smaller number incur substantially higher costs. Such a pattern can make the mean sensitive to high values and can make standard methods that assume roughly symmetric data less suitable. Over-dispersion means that observed variability is greater than a model’s assumptions allow; if present and unaddressed, it can make uncertainty estimates too optimistic. This is a general consideration for cost outcomes, not a statement that over-dispersion was observed or that a particular model was used in this study. The analysis method is not reported in the registry record.

How should uncertainty be assessed?

In general, a confidence interval gives a range of values compatible with the data and the assumptions of the statistical method. It communicates precision: a wider interval indicates less precision than a narrower interval. A confidence interval is not a guarantee that the true value lies within the interval, and its interpretation depends on the model and study design. No confidence interval for the primary cost estimate is reported in the registry record, so its precision cannot be evaluated from the registry information.

A standard deviation and a confidence interval answer different questions. The standard deviation describes variation among observations, while a confidence interval describes uncertainty about an estimated quantity. Reporting both can help readers distinguish heterogeneity in individual costs from uncertainty in the estimated average. The registry identifies standard deviation as the dispersion measure, but does not report its value or an interval for the mean.

What does an observational comparison allow?

The registry describes the study as observational and explicitly warns that its arms are not a like-for-like control comparison. General statistical interpretation distinguishes association from causation. When treatment is not randomly assigned, differences in participant characteristics, disease severity, prior care, or other factors may be related to both treatment choice and costs. These are general examples of possible confounding factors, not confirmed features of this study. The record does not report which factors were measured or whether an adjusted analysis was performed.

Even a carefully adjusted observational analysis depends on the factors measured and the assumptions used. Adjustment can address measured differences under appropriate modeling assumptions, but it cannot automatically remove bias from unmeasured differences. Since the analysis plan and adjustment details are not reported in the registry record, the strength of any comparative inference cannot be assessed.

How should planning illustrations be read?

Planning illustrations based on an observed effect are not evidence that a study had a particular probability of detecting an effect. They are not observed power. The registry’s planning assumptions describe a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect to detect expressed as a stated fraction of the observed effect. Such calculations are hypothetical planning aids under their assumptions, not additional trial findings. The record does not report the trial’s own sample-size justification.

For an observational study, the equal-allocation assumption in a planning illustration should not be mistaken for evidence that the study actually assigned equal numbers to treatment groups. The registry does not report random allocation, and it cautions that the arms are not like-for-like controls. The displayed planning calculations, if consulted, should therefore be understood as illustrative rather than as a description of the study’s design or as proof of an achieved level of power.

The registry lists 54 analyses across 28 outcome measures. In general, examining many outcomes or analyses raises a multiplicity question: the chance of at least one apparently notable result can increase when many statistical tests are considered. Methods such as prespecifying a primary outcome or adjusting for multiple comparisons can help address that issue, but the registry record does not report whether such methods were used. The stated primary cost outcome is distinguishable from the listed secondary outcomes, but the analysis hierarchy and any multiplicity strategy are not reported.

These method concepts describe how to evaluate continuous cost estimates and observational comparisons in general. They do not establish which statistical procedures were used in this study. The model, covariate adjustment, confidence-interval method, handling of cost distributions, and multiplicity approach are not reported in the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 28 outcome measures and 54 analyses. The primary outcome is mean cost per participant per month at Month 12; several secondary outcomes concern response, psoriasis severity, function, disease activity, radiology, and physical measurements. When multiple outcomes or analyses are considered, multiplicity is a general concern because a collection of tests can produce apparently notable findings by chance. The registry record does not report a statistical plan for controlling multiplicity, an outcome hierarchy beyond identifying the primary endpoint, or which analyses were prespecified.

The primary population is defined as the Intent-to-Treat population, including all participants who received at least 1 dose of study medication. Enrollment is 107, but the number included in the primary endpoint analysis is not reported in the registry record. The number with observed Month 12 costs, the handling of participants without those data, reasons for missingness, and any imputation method are also not reported.

Missing data can affect an estimate if the participants with recorded costs differ systematically from those without recorded costs. In general, the consequences depend on why data are missing and on the analysis assumptions. Without a missing-data description or sensitivity analysis, the robustness of the endpoint estimate cannot be assessed. No such results are reported in the registry record.

The record also does not report whether the secondary outcomes used the same analysis population or how incomplete measurements were handled. These gaps limit evaluation of both the endpoint estimates and the broader set of analyses.

11. 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 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry’s adverse-event summary lists All Participants, with 107 at risk for serious adverse events and 0 affected. For other adverse events, it lists 107 at risk and 8 affected. These are registry counts; the record does not give numerical rates or a treatment-group comparison, and no rate should be inferred from them.

The serious-event listing contains no top serious adverse-event terms. The record gives no further event descriptions, definitions, severity grading details, follow-up duration for safety, or information on whether the other events were considered related to treatment. Those details are not reported in the registry record.

These figures should be interpreted as descriptive safety reporting for the listed All Participants group. They do not establish that serious events could not occur, nor do they permit comparison of safety between conventional and biologic therapy. The study is observational, and the registry cautions that the arms are not like-for-like controls. A comparative safety conclusion would require relevant group-level data and analysis, which are not reported in the registry record.

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

The registry record identifies an economic question: the mean cost per participant per month at Month 12 for refractory psoriatic arthritis care. It defines the endpoint broadly, incorporating direct costs and productivity losses, and names the direct cost categories. This clarifies what the intended measure covers, but the numerical mean, standard deviation, and confidence interval are not reported in the registry record.

The study’s observational design means that any comparison between therapies would need careful interpretation. The registry explicitly states that the comparison is not randomized and that the arms are not like-for-like controls. In general, observed cost differences may reflect differences between the people receiving each therapy as well as differences associated with the therapy itself. The record does not report the group-level estimates or adjusted analyses needed to evaluate that possibility.

The primary endpoint is an economic measure, not a direct measure of clinical benefit. Secondary outcomes are listed for response, psoriasis, function, disease activity, radiology, and physical assessment, but numerical results for them are not reported. The stated secondary aims include efficacy, safety, and cost effectiveness; the record does not provide numerical results for those aims.

Accordingly, the registry information supports understanding the intended cost question, the endpoint definition, and key design limitations. It does not establish the average observed cost, whether one therapy had higher or lower costs, whether clinical outcomes differed, or whether the treatments were cost effective. Those conclusions require results and methods not reported in the registry record.

13. Why This Trial Matters Statistically

Economic evaluations can capture resource use that a clinical outcome alone may not describe. This study’s stated cost definition includes pharmacological treatment, hospitalizations, diagnostic examinations, laboratory analysis, specialist visits, transports, and productivity losses. That scope makes clear that the intended endpoint concerns both care-related expenditure and indirect costs, rather than a single cost category.

The record is also a useful example of why design labels matter. Its stated purpose compares conventional and biologic therapy, but the study is observational and the registry cautions that the arms are not like-for-like controls. Statistical interpretation must distinguish a descriptive or associational comparison from a causal estimate. A treatment-cost contrast can be influenced by who received each therapy and by other factors, not only by therapy choice.

The endpoint is a mean, which is a familiar summary for average resource use. For cost data, however, the distribution and variability are important to interpretation because unusually large costs can affect the mean. The record specifies standard deviation as the dispersion measure, but does not report its value or the numerical mean. This illustrates why a clearly defined endpoint is not enough to assess magnitude or precision without the results.

The registry’s broad set of outcome measures and analyses also raises general questions about missing data and multiplicity. The record identifies a primary endpoint and lists secondary outcomes, but does not report the analysis plan, missing-data procedures, or any multiplicity strategy. These details are important for evaluating how dependable and interpretable reported estimates would be. In this record, numerical results and much of that methodological information are not reported.

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 registry record is that it does not report the numerical primary endpoint result. The mean cost at Month 12, its standard deviation, and a confidence interval are not reported in the registry record. Consequently, the level of observed cost and the precision of its estimate cannot be assessed.

The study is observational, and the registry states that the treatment arms are not like-for-like controls. The allocation method, treatment-group definitions, and any adjustment for differences between groups are not reported. This prevents assessment of whether a comparative cost estimate would address confounding or support a causal interpretation.

The primary population is defined by receipt of at least 1 dose, but the number included in the endpoint analysis is not reported. The amount and pattern of missing Month 12 cost data, reasons for missingness, and methods for handling incomplete observations are not reported. These omissions prevent evaluation of how missing information might affect the estimated mean.

The registry lists many outcome measures and analyses, but does not report the statistical analysis plan, the approach to multiplicity, or whether secondary outcomes were prespecified. It also does not report the cost model, any transformation or distributional assumptions, or uncertainty-estimation methods. These details are relevant for assessing the validity and reproducibility of cost analyses.

Finally, the stated aims include efficacy, safety, and cost effectiveness, but the registry record does not provide numerical findings for these aims. The adverse-event summary is descriptive and does not provide a randomized treatment comparison. These limitations reflect what is documented in the registry record and do not establish that unreported analyses were not conducted.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Study Evaluating the Cost of the Treatments of the Refractory Psoriatic Arthritis to the Conventional Therapy — NCT00303186.
• Registry record last updated 2012-07-30; status last verified 2012-06.
• Results first posted 2012-07-30.
• 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 observational study of costs associated with refractory psoriatic arthritis care. Enrollment is listed as 107; the recorded start is 2005-02 and primary completion is 2011-06. The sponsor is Pfizer.

The primary endpoint is mean cost per participant per month at Month 12, measured in Euro/participant-month. It combines direct costs with indirect costs from productivity losses. The defined primary population includes participants who received at least 1 dose of study medication.

The registry lists 28 outcome measures and 54 analyses. It cautions that this is not a randomized comparison and that the arms are not like-for-like controls. The numerical primary cost result, comparative treatment results, analysis plan, and missing-data methods are not reported in the registry record.