Study To Evaluate The Response To Enbrel And The Impact Of Rheumatoid Factor(RF) And Anti-Cyclic Citrullinated Peptide(Anti-CCP) In Rheumatoid Arthritis(RA) Patients: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Study To Evaluate The Response To Enbrel And The Impact Of Rheumatoid Factor(RF) And Anti-Cyclic Citrullinated Peptide(Anti-CCP) In Rheumatoid Arthritis(RA) Patients (NCT04428424), a registered phase not stated study. The primary outcome is Disease Activity Score 28 (DAS28) in Participants With Positive Rheumatoid Factor (RF) and Anti-Cyclic Citrullinated Peptide (ACCP) at Last Follow-up Visit (Month 12).

2. Clinical Question

The record frames the study as an evaluation of local data from Iraqi patients with rheumatoid arthritis who received Enbrel. Its stated focus is whether rheumatoid factor and anti-cyclic citrullinated peptide relate to response, with disease activity represented by DAS28. The central question is therefore about an observed outcome in a registry population, rather than a treatment contrast established through random assignment. Without a reported comparison, the named endpoint alone cannot establish whether antibody status is associated with a different disease activity level.

3. Trial Design

The registry record identifies NCT04428424 as a completed study sponsored by Pfizer. It reports enrollment of 1493 participants and lists rheumatoid arthritis as the condition. The study is described as an evaluation of available local data from the Baghdad Teaching Hospital registry, focused on Iraqi patients with rheumatoid arthritis treated with Enbrel. The retrospective data collection period is described as approximately 7 years.

The listed intervention is Enbrel, classified as a drug, and the arm description says that patients with rheumatoid arthritis received Enbrel for their disease. The record does not describe a control treatment or an untreated arm. It also states that allocation was not reported and that the study is not a randomized comparison. The record therefore does not establish a like-for-like control comparison from which to separate treatment effects from other differences between groups.

The recorded study start date is 2020-07-05, and the primary completion date is 2020-08-30. The listed primary outcome is the mean DAS28 among participants positive for rheumatoid factor and anti-cyclic citrullinated peptide at the last follow-up visit, identified as Month 12. Four outcome measures are listed, while the registry record reports no analyses. The number of participants evaluable for the primary outcome is not reported in the registry record. Enrollment should not be interpreted as the count analyzed for this endpoint.

The registry record does not report further details of the protocol, recruitment process, eligibility criteria, treatment exposure, or the statistical analysis plan. These omissions limit how specifically the design can be reconstructed from the posted record. In particular, the registry information does not explain how antibody-status groups were defined or compared, or whether follow-up and outcome ascertainment were consistent across all enrolled participants.

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: Analysis was performed on all participants who were included in this study. Here "overall number of participants analyzed" signifies participants evaluable for this outcome measure and "number analyzed" signifies participants evaluable for this outcome measure for specified rows.

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: Analysis was performed on all participants who were included in this study.

6. Primary Endpoint

The registry lists the primary outcome as Disease Activity Score 28 (DAS28) in Participants With Positive Rheumatoid Factor (RF) and Anti-Cyclic Citrullinated Peptide (ACCP) at Last Follow-up Visit (Month 12), measured over Month 12 visit during retrospective data collection period of approximately 7 years.

The primary endpoint is the mean Disease Activity Score 28 (DAS28) in participants positive for rheumatoid factor and anti-cyclic citrullinated peptide at the last follow-up visit, identified as Month 12. The record describes this as a continuous measure reported in units on a scale, with the mean and standard deviation as the intended summaries. The actual mean, standard deviation, and number evaluated are not reported in the registry record.

DAS28 is described as combining counts of swollen and painful joints using a 28-joint assessment, erythrocyte sedimentation rate, and the patient's global assessment of disease activity. The global assessment is participant-rated, transformed to a scale ranging from 0 to 10, with higher values indicating higher activity. The record describes DAS28 values less than or equal to 3.2 as low disease activity and values greater than 3.2 to 5.1 as moderate to high disease activity.

General: A composite measure can bring multiple clinical features into a common summary, which may make overall disease activity easier to describe than considering each component separately. A mean gives the average score among the people assessed; a standard deviation describes how dispersed their scores are around that average. Neither summary is reported for this endpoint, so the registry entry does not show the level or variability of DAS28 in the named group. A score at a particular follow-up visit also describes that time point; without a reported baseline value or change analysis, it does not by itself describe improvement over time.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

General: The registry names the mean and standard deviation for a continuous primary outcome. These summaries answer different descriptive questions. The mean represents the average DAS28 among participants with an observed endpoint, while the standard deviation indicates how much individual scores vary around that average. A mean without a standard deviation gives limited information about the distribution of participant scores; a standard deviation without the mean does not indicate the group's average disease activity. Neither statistic is reported for this endpoint, so no numerical description of its observed distribution can be made.

What would a confidence interval describe?

General: A confidence interval is an uncertainty summary for an estimated quantity, calculated using a statistical method and assumptions about the data. For a mean, it can communicate how precisely the population mean is estimated from the analyzed participants. Its width is influenced by the amount of information and the variability in the outcome, as well as the analysis method. The registry record does not report a confidence interval or the inputs required to reconstruct one. No interval should be inferred from enrollment alone, because the outcome-specific evaluable count and outcome variability are not reported.

What can a comparison test establish?

General: A statistical test can evaluate evidence against a specified null hypothesis, such as no difference between defined groups, when the groups, outcome, and analysis are stated. A p-value is not an estimate of the size or clinical importance of a difference. It is also not a substitute for reporting group results and uncertainty. The registry record reports no analyses, p-values, or contrast between antibody-status groups. It therefore gives no test-based evidence about whether DAS28 differs by rheumatoid factor or anti-cyclic citrullinated peptide status.

The endpoint is described for participants positive for both markers. That is an outcome definition, not a complete statistical comparison. To estimate an antibody-status association, the registry would need to report the relevant group estimates and the comparison method, as well as how participants were assigned to the groups. Those details are not reported in the registry record. Because treatment was given to the described participants and no control treatment is listed, the record also does not establish a randomized treatment contrast.

Why does the analysis population matter?

General: An analysis population is the set of participants whose data contribute to a particular result. The enrolled population, the population with follow-up, and the population with an evaluable endpoint can differ. Their distinctions matter because missing outcome measurements can affect both precision and the interpretation of an estimate. The record explains that its analyzed counts refer to participants evaluable for the outcome, but it does not state the actual count for the primary endpoint or describe missing-data handling. No assumption about complete follow-up or how missing observations were treated is warranted.

The record lists a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation in its sample-size assumptions. It describes those assumptions as a planning illustration based on an observed effect, with the effect to detect expressed as a stated fraction of that effect. This is a planning framework, not evidence that the study used those conditions in its own design or analysis. The record does not report the corresponding participant counts for planning, and it does not report a sample-size justification for the registry study. Planning illustrations are not observed power and cannot stand in for a result.

General: Over-dispersion refers to greater variability than a statistical model assumes. If present, it can make standard errors and tests based on an insufficient-variability assumption unreliable. Whether over-dispersion is relevant depends on the outcome and analysis model. The primary endpoint is a continuous DAS28 measure summarized by a mean and standard deviation, and no model-based analysis or evidence about over-dispersion is reported in the registry record. It would therefore be inappropriate to assert that a particular model was used or that over-dispersion was assessed.

The record also does not report whether the analysis adjusted for participant characteristics, how repeated measurements were handled, or whether results were calculated from raw data or a summary dataset. These are not details that can be reconstructed from the endpoint title. They matter because analysis choices can affect estimates and their uncertainty, especially when groups differ or measurements are incomplete. Without a posted statistical plan and analysis output, no specific adjustment, model, or inferential procedure can be attributed to this study.

General: Descriptive estimates and inferential estimates serve related but distinct purposes. A descriptive mean characterizes the observed participants, whereas an inferential estimate seeks to quantify a broader population quantity under specified assumptions. A registry-based analysis can be informative about its recorded population, but the population to which a result generalizes depends on the selection process and completeness of data. The registry record gives the local setting and population description, but does not report enough information about selection, endpoint completeness, or analysis to evaluate generalizability statistically.

Overall, the methods that can be identified are the continuous endpoint definition, its intended mean and standard deviation summaries, and the stated planning assumptions. The statistical test, precision estimate, actual analysis population, missing-data method, and adjustment strategy are not reported in the registry record. The absence of those details is important: it leaves the numerical result and the basis for any inferential conclusion unavailable.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists four outcome measures, but does not report analyses or describe a multiplicity strategy. Multiplicity concerns the increased chance of a false-positive finding when multiple outcomes, groups, or hypotheses are tested. General: methods such as prioritizing a primary outcome or adjusting inference may address this issue, but the registry record does not state whether any such approach was planned or applied. The named primary endpoint gives an outcome priority in the record; it does not reveal how the other listed outcomes were analyzed or interpreted.

Missing-data handling is not reported in the registry record. The record defines the analyzed population as participants evaluable for an outcome, but does not provide the number evaluable for the primary endpoint, the number with missing Month 12 scores, reasons for missingness, or a method for addressing missing observations. Without these details, the completeness of follow-up and the potential influence of missing outcomes cannot be assessed. The enrollment count of 1493 should not be treated as the number contributing to the primary analysis.

The record does not report whether all enrolled participants were included in each outcome analysis, whether any participants were excluded, or how repeated visits were handled. It also does not describe a statistical analysis population beyond its general definition of evaluable participants. These omissions prevent assessment of whether the analyzed participants represent the enrolled registry population.

Because no analysis results are posted, there is no basis to assess multiplicity-adjusted findings, missing-data sensitivity analyses, or consistency across outcomes. These are reporting gaps rather than evidence that a particular method was or was not used.

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

The registry record establishes that a completed study evaluated local data from Iraqi patients with rheumatoid arthritis who received Enbrel. It names a primary outcome: mean DAS28 at Month 12 among participants positive for rheumatoid factor and anti-cyclic citrullinated peptide. It also describes how DAS28 is constructed and identifies activity categories. These details clarify the question and the intended outcome, but they do not provide the result.

The record does not report the primary outcome mean, standard deviation, evaluable count, confidence interval, or statistical test. It also does not post a comparison by antibody status. Therefore, the available record cannot quantify the observed disease activity in the named group or determine whether the score differed across antibody groups. It also cannot establish a treatment effect, because a control group and randomized treatment comparison are not described.

General: An observed outcome in a treated registry population can describe what was recorded among the participants assessed. It does not, on its own, identify what would have happened to comparable participants under a different treatment or without treatment. Such causal interpretation requires a suitable design and analysis to address competing explanations, including differences between groups. This registry entry does not provide the comparison or analysis details needed for that interpretation.

The record's completed status and enrollment count do not resolve these limits. Enrollment is not an outcome estimate, and completion status does not demonstrate that results were reported. Nor does the absence of posted analyses show that the study found no association or no change. It means the registry record does not provide results from which the direction, magnitude, or precision of an association or response can be evaluated.

The defensible conclusion is narrow: the study's registry description concerns DAS28 and antibody status in Enbrel-treated patients, but its posted information does not answer the quantitative primary question. No claim that treatment is effective or ineffective, or that antibody status predicts response, follows from the information recorded.

12. Why This Trial Matters Statistically

This study raises a useful statistical distinction between stating a clinical question and reporting evidence that answers it. The registry identifies a population, a treatment context, antibody markers of interest, and a continuous disease-activity endpoint. Yet the primary endpoint's numerical result and analysis are not reported in the registry record. A clear endpoint definition is valuable, but it cannot substitute for an estimate and its precision.

The record also illustrates why enrollment and analysis counts should be distinguished. It reports enrollment of 1493, while defining analyzed participants as those evaluable for the outcome. The endpoint-specific count is not reported. Readers therefore cannot judge how much data support the intended result or whether follow-up completeness may affect its interpretation.

Another important issue is the distinction between an outcome description and a comparison. The primary endpoint concerns participants positive for both rheumatoid factor and anti-cyclic citrullinated peptide, but no comparison with other antibody-status groups is posted. A group-specific mean would describe that group; evidence about an association requires a defined comparison and a reported analysis. Similarly, an outcome among treated participants does not by itself estimate a treatment effect.

The registry's planning assumptions also highlight the difference between design planning and observed results. Stated assumptions about significance level, allocation, and an effect to detect do not show that an analysis was conducted under those conditions. Planning calculations cannot replace outcome estimates, uncertainty intervals, or transparent reporting of the analysis population.

These points matter for clinical research interpretation broadly: conclusions depend not only on what outcome was intended, but also on who contributed data, what comparisons were made, and how uncertainty was quantified. In this record, the question is identifiable, while the statistical evidence needed to answer it is not reported.

13. 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 registry record describes retrospective data collection from the Baghdad Teaching Hospital registry over approximately 7 years, but does not provide detail about how patients entered the registry, how eligibility was applied, or how the data were collected. Those omissions limit assessment of selection and measurement processes. The record concerns Iraqi patients, and information needed to assess applicability to other patient populations is not reported in the registry record.

All patients in the listed arm are described as receiving Enbrel. No control treatment is described, allocation is not stated, and the record identifies the study as not a randomized comparison. This limits the ability to separate treatment-related changes from other explanations. Although the study's stated focus includes rheumatoid factor and anti-cyclic citrullinated peptide, the record does not report comparative results by antibody status or describe how such groups were formed.

The primary outcome is identified at Month 12, but the registry record does not report the endpoint mean, standard deviation, or evaluable participant count. It also does not report baseline DAS28, changes over time, missing-data methods, or analysis details. This prevents assessment of the observed outcome, its precision, follow-up completeness, and the influence of analytic choices.

The record lists four outcome measures and no analyses, but does not describe multiplicity handling or explain how the other outcomes relate to the primary endpoint. Safety fields for the listed etanercept group show zero for participants at risk and affected for the recorded serious and other event categories; the registry record does not clarify whether these entries reflect no events, absent data, or another reporting convention. No serious-event terms are listed. These fields should not be used to infer a complete safety assessment.

14. Related Tutorials

15. Related Statistical Calculators

16. Sources

• ClinicalTrials.gov: Study To Evaluate The Response To Enbrel And The Impact Of Rheumatoid Factor(RF) And Anti-Cyclic Citrullinated Peptide(Anti-CCP) In Rheumatoid Arthritis(RA) Patients — NCT04428424.
• Registry record last updated 2021-09-09; status last verified 2021-08.
• Results first posted 2021-09-09.
• 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.

17. Record Summary

NCT04428424 is a completed registry study sponsored by Pfizer, concerning Iraqi patients with rheumatoid arthritis treated with Enbrel. The record reports enrollment of 1493 and describes retrospective evaluation of local data from the Baghdad Teaching Hospital registry over approximately 7 years. The listed dates are 2020-07-05 for study start and 2020-08-30 for primary completion.

The named primary outcome is mean DAS28 at Month 12 among participants positive for rheumatoid factor and anti-cyclic citrullinated peptide. The record describes DAS28 components and activity thresholds, but does not report the outcome mean, standard deviation, evaluable count, or statistical analysis. It lists four outcome measures and reports no analyses.

No randomized comparison or control treatment is described. The record does not report antibody-status comparisons, missing-data methods, or a statistical analysis plan. Thus, it defines the intended clinical question but does not provide the numerical results required to assess the primary endpoint or its precision.