Benefits of Injectable Abatacept Using Magnetic Resonance Imaging (MRI) in Rheumatoid Arthritis (RA) Patients: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Benefits of Injectable Abatacept Using Magnetic Resonance Imaging (MRI) in Rheumatoid Arthritis (RA) Patients (NCT01351480), a na phase 3 study. The primary outcome is Number of Participants With an Improvement in Bone Edema/Osteitis on Low-field MRI in Rheumatoid Arthritis Patients on Weekly SC Abatacept in Combination With Methotrexate Over a 12-month Period..

2. Clinical Question

3. Trial Design

The registry record describes a phase 3, single-group study of abatacept in rheumatoid arthritis. It lists 34 participants as enrolled and the study status as completed. The study started in 2011-06, with primary completion in 2014-01. The arm description specifies open-label abatacept use for 12 months. Masking is listed as none, and allocation is not applicable.

These design details are important for interpreting the findings. Without a separate control group, the observed MRI changes can describe what happened during follow-up among participants with available MRI assessments, but they cannot isolate the effect of abatacept from other explanations. Changes over time may also reflect the natural course of disease, concurrent care, measurement variation, or changes in the participants followed. The record does not describe a randomized or blinded comparison.

The primary-outcome description states that MRIs from 27 patients were assessed at baseline and week 48. That is the population specified for the MRI assessment, not necessarily the full enrolled group. Reasons why the MRI population is smaller than total enrollment, and details of participant disposition, are not reported in the registry record. It is therefore not possible to determine from these details whether all enrolled participants started treatment, completed follow-up, or were included in other outcome analyses.

The primary-outcome title refers to weekly subcutaneous abatacept in combination with methotrexate. The listed intervention is abatacept, and the arm description mentions open-label abatacept without specifying methotrexate. The registry record does not resolve this difference in regimen detail. Additional protocol information, such as eligibility criteria, dose, adherence procedures, or the intended handling of concomitant treatment, is not reported in the registry record.

The registry names Arthritis & Rheumatic Disease Specialties Research as sponsor. Although the study is marked completed, completion status alone does not establish that every planned analysis was performed or that all results were posted. No analysis records are listed. The registry record does not report the statistical analysis plan, a sample-size justification, interim analyses, or the planned approach to missing observations.

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: osteitis on the MRIs from 27 patients at baseline and week 48

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 Number of Participants With an Improvement in Bone Edema/Osteitis on Low-field MRI in Rheumatoid Arthritis Patients on Weekly SC Abatacept in Combination With Methotrexate Over a 12-month Period., measured over MRIs at Baseline and Week 48.

The primary endpoint is the number of participants with improvement in bone edema/osteitis on low-field MRI, with MRI assessments at baseline and week 48. The outcome description specifies assessment of 25 anatomical locations in the wrist and hand. Bone edema/osteitis is scored by volume of the original articular bone on a 0-3 scale in 0.5 increments; each increment represents 33% of the volume of the peripheral 1 cm of original, eroded plus residual, articular bone.

As a general statistical concept, an MRI endpoint can quantify anatomical features using a structured measurement approach rather than relying only on a participant's or clinician's overall impression. A count of participants classified as improved converts individual MRI assessments into a binary outcome: each assessed participant is classified as improved or not improved, according to a rule. The registry record does not report the rule or threshold used to define improvement, nor the observed number classified as improved.

The endpoint is intended to describe change in an imaging feature over the stated follow-up period. It does not, by itself, establish that changes in MRI scores correspond to a particular clinical benefit. The relationship between this imaging outcome and the listed clinical outcomes is not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a participant count represent?

The primary outcome is stated as a number of participants with improvement. In general, this is a binary endpoint: each participant is classified into one of two categories, such as improved or not improved, and the result is expressed as a count or proportion for a defined analysis group. A meaningful count requires a clear improvement rule, a defined denominator, and a description of how participants without usable follow-up measurements are handled. The registry record gives the outcome wording and identifies MRI data from 27 patients at baseline and week 48, but does not report the improvement rule, the observed count, or an analysis denominator beyond that description.

A binary endpoint differs from a continuous score. It does not retain all the detail in the underlying MRI scale: participants just above and just below a classification threshold may be placed in different categories despite similar scores, while differing degrees of improvement within the same category may be treated alike. This is a general property of dichotomizing measurements; the registry record does not state the threshold used for this endpoint.

What can a single-group change show?

In a single-group study, measurements at baseline and follow-up can describe change among participants assessed at both times. That is not the same as estimating a treatment effect against a concurrent comparator. In general, a control group helps distinguish changes associated with the intervention from changes that might also occur through time, other care, or features of the enrolled population. This study is recorded as single-group, with no allocation and no masking, so a treatment-versus-control contrast is not defined by the listed design.

For a participant-level binary outcome, the analysis might report a count, a proportion, or an estimate with an uncertainty interval. Which approach was used, and whether any adjustment was made, are not reported in the registry record. No result should be inferred from the endpoint label alone.

How should precision be understood?

General: a confidence interval communicates statistical uncertainty around an estimate. A narrower interval indicates greater precision under the method's assumptions, while a wider interval indicates less precision. It does not show that the assumptions are correct, remove bias, or establish clinical importance. A p-value, in general, measures how unusual the observed data would be under a specified null model; it is not the probability that a treatment works or that the null hypothesis is true. The registry record does not report a confidence interval, p-value, or the method used for inference on the primary outcome.

For a binary count, precision is affected by the number of participants analyzed and how many meet the outcome definition. The registry record's MRI population description is 27 patients with scans at baseline and week 48, but it does not provide the outcome count needed to characterize its statistical uncertainty. Nor does the record report whether the analyses used all participants with paired MRI data or another defined population.

Why does over-dispersion matter?

General: over-dispersion occurs when observed variation is greater than a statistical model assumes. If a count model assumes that observations vary less than they actually do, standard errors may be too small and confidence intervals too narrow. The primary endpoint is described as a participant count for a binary outcome, not as a repeated event count. The registry record does not identify a count model or report repeated-event analyses, so there is no basis to claim that over-dispersion was assessed or that it affected the result.

What do planning calculations mean?

General: sample-size calculations describe the number of participants that might be needed under stated assumptions to detect a specified effect with a chosen significance level and power. They are design illustrations, not results from enrolled participants and not observed power. A calculation based on an observed effect is especially dependent on that effect estimate and can be unstable when the estimate is uncertain. The registry record does not report the trial's own sample-size justification, and the primary effect is not reported in the registry record. Any planning illustration should therefore be understood only through its stated assumptions, not as evidence that the study had a particular probability of detecting an effect.

The registry record does not state whether the primary analysis used an exact method, a normal approximation, a model, or another approach. It also does not report assumptions about the distribution of outcomes, the handling of missing MRI data, or whether sensitivity analyses were conducted. No recalculated effect estimate is available from the registry entries described for this study.

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("Abatacept")
n      <- c(27)
events <- c(27)
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  Abatacept  27  27  100.0  87.2  100.0  87.5  100.0  87.7  99.9

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists five outcome measures overall and names secondary outcomes concerning improvement in DAS score, DAS 28 scores at baseline and follow-up visits, clinical response, and adverse events. Multiple outcomes can create a multiplicity question: when several hypotheses are tested, the chance of at least one apparently notable result can increase if each is assessed separately. Statistical plans may address this through prespecified outcome hierarchies, adjusted significance thresholds, or other methods. The registry record does not report whether any multiplicity strategy was planned or used, and it does not report outcome analysis results.

The primary MRI population is described as 27 patients with scans at baseline and week 48. Enrollment was 34. The registry record does not give participant flow, explain the difference between these counts, or identify whether any participants were excluded from the primary analysis. It also does not state whether missing MRI measurements were imputed, whether analyses were restricted to participants with both scans, or whether sensitivity analyses were performed. The amount and pattern of missing data are therefore not reported in the registry record.

Analysis populations, such as an intention-to-treat population or a per-protocol population, are not reported in the registry record. It is not possible to determine which participants were included in the analyses of the primary or secondary outcomes. The record lists no analysis records, so specific analysis methods and handling of missing observations cannot be verified from the registry entries.

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 0% reporting threshold.

The registry record lists 27 participants at risk for serious adverse events and 0 affected. It also lists 27 participants at risk for other adverse events and 0 affected. These are the posted counts; they do not establish that no adverse events occurred outside the categories or reporting period represented by those fields. The record does not list serious adverse event terms.

The deaths field is null. A null entry is not the same as a reported count of zero, so the number of deaths is not reported in the registry record. The record also does not provide event descriptions, severity details, timing, attribution to treatment, or participant-level follow-up for these safety fields. The counts should therefore be read as registry entries for the stated groups, not as a complete account of all safety information collected during the study.

Because the study is single-group and the registry record does not give a comparative safety analysis, these figures do not estimate a difference in adverse-event risk relative to another treatment or control group. The listed risk counts and affected counts alone do not establish causal attribution.

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

The registry record describes a study designed to assess improvement in bone edema/osteitis on low-field MRI during open-label abatacept treatment in rheumatoid arthritis. It specifies MRI assessments at baseline and week 48 and identifies MRI data from 27 patients. However, the number who improved is not reported in the registry record. The record also does not report an estimate of the amount of change, an uncertainty interval, or a test of the primary outcome.

That distinction matters: an endpoint description tells readers what investigators intended to measure, but it does not tell them what the measurements showed. Without the observed outcome and its analysis details, the frequency of MRI improvement and its precision cannot be assessed. The available registry information therefore does not establish whether improvement was common or uncommon in the assessed participants.

Even if the primary outcome result were reported, the single-group design would limit causal interpretation. An observed before-and-after change would not, on its own, show what would have happened over the same period without the intervention. The design includes no concurrent comparator, and masking is listed as none. These features constrain comparisons and may affect how findings can be interpreted, though the registry record does not state whether they changed any specific assessment.

The MRI outcome also should not be treated as interchangeable with the listed clinical outcomes. The record names DAS-related measures and clinical response outcomes, but their results and the analysis of any relationship with MRI change are not reported in the registry record. The MRI endpoint alone cannot establish clinical benefit, nor does it establish an individual participant's experience.

The safety entries report 0 serious adverse events and 0 other adverse events among 27 at risk in each category, while the deaths field is null. Those entries are limited registry data, not a comparative safety estimate or a complete account of events. The appropriate interpretation is therefore descriptive and bounded by what the record actually reports.

14. Why This Trial Matters Statistically

Statistically, this trial illustrates why a defined endpoint and an observed result are both needed to interpret clinical research. The endpoint description is relatively specific about the imaging feature, anatomical locations, scoring scale, and assessment times. Yet without the number of participants classified as improved, the outcome definition, and an uncertainty estimate, readers cannot quantify the finding or judge its precision.

The design also makes the distinction between change and comparison especially important. A single-group study can document measurements over time, but it does not provide the concurrent control contrast used to assess whether a difference is attributable to treatment rather than other influences. The open-label design and absence of masking are further features to consider when interpreting outcome assessment, while the record does not report procedures intended to address them.

The difference between enrollment of 34 and the MRI population description of 27 patients illustrates why participant flow and analysis populations matter. Without information about missing measurements, exclusions, or analysis sets, even a posted result would be harder to interpret. The registry record does not report these details.

Finally, the record lists several clinical outcomes alongside the MRI endpoint but does not report their results or explain how multiple outcomes were handled. This prevents assessment of consistency across outcome types and leaves the relationship between imaging and clinical measures unresolved. These are general issues in endpoint interpretation, multiplicity, missing data, and causal inference—not evidence for or against a treatment effect in this particular study.

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.

Several trial-specific limitations of interpretation follow from the registry entries. First, no primary-outcome result is reported: the record names a count of participants with MRI improvement but does not give the count, a proportion, or an uncertainty estimate. The improvement threshold is also not reported in the registry record, so the classification rule cannot be evaluated.

Second, the study is single-group, open-label, and has no concurrent comparator. Its design can describe measurements during follow-up but cannot distinguish treatment-associated change from other explanations as a randomized comparison could. No masking is listed, and the registry record does not describe any procedures for blinded image assessment.

Third, enrollment is 34, whereas the primary-outcome description refers to MRIs from 27 patients at baseline and week 48. The registry record does not explain the difference, provide participant disposition, or report how missing MRI measurements were handled. The analysis population for the primary outcome and the populations used for secondary outcomes are not reported in the registry record.

Fourth, the primary-outcome title specifies abatacept in combination with methotrexate, while the listed intervention and arm description do not explicitly name methotrexate. The registry record does not clarify this regimen detail. It also does not report the statistical plan, sample-size justification, interim analyses, multiplicity handling, or analysis methods. The absence of these details limits assessment of how outcomes were selected and analyzed; it does not establish that a particular procedure was or was not used.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Benefits of Injectable Abatacept Using Magnetic Resonance Imaging (MRI) in Rheumatoid Arthritis (RA) Patients — NCT01351480.
• Registry record last updated 2017-03-13; status last verified 2017-01.
• Results first posted 2017-03-13.
• 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

This completed phase 3 study enrolled 34 participants with rheumatoid arthritis and is recorded as a single-group, open-label study of abatacept. The arm description specifies open-label treatment for 12 months. The primary outcome concerns the number of participants with improvement in bone edema/osteitis on low-field MRI between baseline and week 48; its population description refers to MRI data from 27 patients.

The registry record does not report the primary outcome count, an effect estimate, a confidence interval, or a p-value. It lists 0 serious adverse events and 0 other adverse events among 27 at risk in each category; deaths are not reported in the registry record. No analysis records are listed. The design has no comparator arm, and analysis methods, missing-data handling, and the statistical plan are not reported in the registry record.