Baricitinib in Relapsing Giant Cell Arteritis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Baricitinib in Relapsing Giant Cell Arteritis (NCT03026504), a na phase 2 study. The primary outcome is Adverse Events.

2. Clinical Question

3. Trial Design

This was a phase II, single-institution, open-label pilot study of baricitinib in relapsing giant cell arteritis. The registry record reports that the study was completed and lists enrollment of 15 participants. It describes a single-group model, with no allocation to separate treatment groups. Consequently, the study provides a description of outcomes among participants receiving the study regimen, not a randomized comparison.

Baricitinib was given orally at 4 milligrams daily for 52 weeks. Participants were taking prednisone at the start of the study, and prednisone was reduced on a standardized tapering schedule while baricitinib continued. The record does not state further details about the taper schedule, such as its timing or dose steps, so those details cannot be inferred.

The study was open label: masking was not used. In general, this means participants and study personnel know which regimen is being given. Awareness of treatment can affect subjective assessments, reporting, and decisions about outcome classification. This matters when interpreting outcomes that depend on symptoms or clinical judgment. The primary outcome was adverse events, which may also be influenced by how events are elicited, recorded, and judged.

The primary outcome timeframe was 52 weeks. Secondary outcomes included giant cell arteritis relapse, erythrocyte sedimentation rate, and C reactive protein. The registry record does not report the detailed assessment schedule or the operational definitions for these secondary outcomes. It also does not report eligibility criteria, baseline characteristics, or a fuller account of the analysis population. These omissions limit the ability to assess how the enrolled group relates to other people with the condition or how outcomes were measured over time.

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

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 Adverse Events, measured over 52 weeks.

The primary endpoint was the percentage of participants who experienced at least one adverse event during 52 weeks. An endpoint expressed this way is a participant-level summary: a person is counted if one or more qualifying events occurred during the specified period. It does not, by itself, describe how many separate events occurred, how long they lasted, or their severity.

Adverse-event outcomes are used to characterize harms observed during a study. They are relevant to describing the experience of participants while receiving the study regimen, but a single-group study cannot determine whether an event was caused by the treatment. Events can arise from the underlying condition, other medicines, or other circumstances. Attribution requires clinical assessment, and the registry record does not report those judgments in detail.

The registry record names the endpoint and timeframe but does not report a primary-endpoint percentage. It gives counts for serious and other adverse events, which should not be treated as a substitute for a clearly reported percentage without knowing the endpoint definitions and analysis details. The record also does not explain how missing observations or participants who did not complete follow-up were handled. Thus, the endpoint description identifies what the study intended to summarize, while the posted counts give only part of the information needed to interpret that summary.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a single-group result estimate?

In general, a single-group study describes outcomes observed among people receiving a particular regimen. For a binary outcome such as whether a participant experienced at least one event, the basic estimate is a proportion among participants assessed. That proportion is meaningful only alongside a clear numerator, denominator, outcome definition, and account of missing observations. The registry record gives counts at risk and counts affected for the safety categories, but it does not report a primary-endpoint percentage or describe missing-data handling.

Because this study has no concurrent comparator, its results do not estimate a difference between treatment groups. A change observed during follow-up could have several explanations, including the study regimen, the natural course of the condition, prednisone tapering, other care, or random variation. A comparison with an external group would require additional assumptions and is not reported in the registry record. The posted results should therefore be interpreted descriptively rather than as a causal estimate.

What would a confidence interval add?

In general, a confidence interval expresses the uncertainty around an estimated quantity under a statistical model. For a proportion, it helps show how imprecisely an observed event frequency may represent the population from which participants were drawn. Estimates based on limited information can be uncertain even when their point values look clear. The registry record does not report confidence intervals for the primary outcome or the posted adverse-event counts, so the precision of those estimates cannot be assessed from the reported results.

A confidence interval would not resolve the design’s lack of a comparator. It can describe uncertainty around a single-group estimate, but it cannot remove confounding or show what would have happened under an alternative regimen. Statistical precision and causal interpretation are separate issues: even a precisely estimated proportion would remain a description of this group unless an appropriate comparison supported a treatment-effect interpretation.

How should the planning illustrations be read?

The planning illustrations associated with the posted results are not observed power. They use a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. They are based on the observed effect and consider detecting a stated fraction of that effect. The registry record’s actual study is single group, so the assumed two-arm allocation is a hypothetical planning framework, not the design used in this trial.

In general, sample-size planning asks how many participants per arm might be needed under stated assumptions to detect a specified effect with a selected probability, while controlling a chosen error rate. Such calculations depend on the endpoint, the assumed effect, the analysis method, and the study design. They do not show the probability that a completed trial’s findings are true, and they cannot retrospectively establish that the study had adequate power. The registry record does not report a sample-size justification for the trial’s own design. Numerical planning outputs should be understood as illustrations under assumptions, not as observed trial findings.

The normal approximation is a simplifying method for planning. In general, approximations can be less reliable when event counts or sample sizes are limited, especially for binary outcomes with uncommon events. The record does not describe alternative planning methods or justify the approximation for this study. It also does not provide the numerical planning outputs in the registry information, so no planning estimate can be interpreted from those details alone.

Why do outcome definitions and analysis details matter?

For a binary adverse-event outcome, the definition determines what qualifies as an event and how multiple events for one participant are represented. An outcome counting participants with at least one event differs from an outcome counting every event. The primary description specifies a participant-level threshold, but the record does not explain how that endpoint was reconciled with the serious and other adverse-event counts. It also does not state whether events were coded using a particular classification system or how seriousness was determined.

Analysis populations matter because the number enrolled need not be the same as the number with evaluable outcome data. In general, an analysis should identify who contributed to the estimate and how participants with incomplete follow-up were treated. The registry record reports enrollment and safety denominators, but it does not provide a fuller description of analysis populations or missing-data procedures. Without those details, the denominator’s relationship to follow-up completion cannot be assessed.

Finally, the record does not report inferential analyses, adjusted estimates, or a statistical analysis plan. Therefore, there is no basis in the registry record for describing a prespecified model, adjustment strategy, or formal test for the primary outcome. General statistical concepts can clarify what such methods would address, but they cannot fill gaps in the reported analysis.

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("Baricitinib Therapy")
n      <- c(15)
events <- c(14)
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  Baricitinib Therapy  15  14  93.3  68.1  99.8  70.2  98.8  69.8  98.4

11. Multiplicity, Missing Data and Analysis Populations

The record lists a primary adverse-event outcome and secondary outcomes of giant cell arteritis relapse, erythrocyte sedimentation rate, and C reactive protein. When a study assesses several outcomes, the chance of at least one apparently unusual result can increase if many statistical tests are performed. In general, multiplicity procedures may be used to control that risk, or outcomes may be interpreted as exploratory. The registry record does not report a multiplicity plan, a hierarchy among the secondary outcomes, or inferential results for those outcomes.

The record reports no analyses. It therefore does not provide statistical tests, adjusted estimates, or a stated approach for handling multiple comparisons. No claim about statistical significance or a multiplicity adjustment can be made from the posted information.

Missing data can also affect interpretation. In general, incomplete follow-up may alter an observed event proportion if participants with missing information differ from those with complete information. Methods for addressing this include defining an analysis population, describing missingness, and stating any assumptions used to handle unavailable outcomes. The registry record does not report missing-data methods, the number with complete primary-outcome data, or reasons for any incomplete follow-up. The reported safety denominators alone do not establish how missing observations were treated.

The record also does not describe the detailed population used for each outcome. Without that information, readers cannot tell whether all enrolled participants contributed to every result or whether outcome-specific populations differed. These gaps do not prove that data were missing or that a particular analysis was conducted; they mean the handling is not reported in the registry record.

12. 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: thrombocytopenia (6.7%).

The registry record reports 1 participant with a serious adverse event among 15 at risk, 14 with other adverse events among 15 at risk, and 0 deaths. These are counts for the Baricitinib Therapy group. The record also lists thrombocytopenia at 6.7% among serious adverse-event terms. These entries describe what was recorded; they do not establish that baricitinib caused an event.

Serious adverse events and other adverse events are different categories, but the registry information does not explain their operational definitions or whether a participant could appear in both. The counts should not be added to create an overall participant count or interpreted as separate, non-overlapping groups. The primary endpoint is described as the percentage experiencing at least one adverse event, while the record reports the safety categories as counts. It does not report a primary-endpoint percentage.

In general, adverse-event interpretation depends on the event definition, follow-up completeness, clinical context, and how treatment attribution was assessed. Those details are not reported in the registry record. The counts are useful as a descriptive record of events during the study, but they cannot establish comparative risk or causality.

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

The result establishes that the registry recorded adverse events in participants receiving baricitinib while prednisone was being tapered. The safety entries include 1 participant affected by a serious adverse event among 15 at risk, 14 affected by other adverse events among 15 at risk, 0 deaths, and thrombocytopenia listed at 6.7% among serious adverse-event terms. These figures describe the posted safety record over the study’s stated timeframe; they do not, on their own, explain why events occurred.

The study design limits what can be concluded. It was open label and single group, with no randomized comparator. There is therefore no direct estimate of how the adverse-event experience differed from another treatment or from the course of the condition without baricitinib. A reported event could relate to the regimen, the disease, prednisone tapering, other care, or other factors. The registry record does not provide a basis for separating these possibilities.

The primary outcome was intended to capture the percentage experiencing at least one adverse event over 52 weeks. The registry record does not report that percentage as a primary result, nor does it provide a confidence interval or detailed analysis population. The secondary outcome names are recorded, but their results are not reported. Thus the available record does not establish a complete balance of safety and disease activity outcomes.

These results should not be read as proof that baricitinib is beneficial, harmful, or equivalent to another approach. A descriptive count is not a treatment-effect estimate, and the absence of a reported outcome is not evidence that the outcome did not occur. The appropriate interpretation is limited to the events and counts the registry record actually reports, with uncertainty about the completeness and analytic handling of the data.

14. Why This Trial Matters Statistically

This trial is statistically informative as an example of the difference between describing outcomes and estimating a treatment effect. Its single-group design can document what was recorded among participants receiving baricitinib alongside a prednisone taper. It cannot create the counterfactual comparison needed to determine whether outcomes would have differed under another regimen. That distinction remains important even when a study has a clearly stated endpoint and follow-up period.

The primary endpoint is participant-level: whether someone experienced at least one adverse event during 52 weeks. Such an endpoint compresses potentially varied experiences into a binary summary. It can be useful for describing how widespread an outcome was, but it omits event count, duration, severity beyond the separate serious classification, and timing. The registry record’s separate serious and other event counts underscore why endpoint definitions and reporting categories should be read carefully.

The trial also illustrates the importance of complete results reporting. A stated primary outcome is not the same as a reported estimate. Without the primary-endpoint percentage, uncertainty interval, analysis population, and missing-data description, readers have limited ability to evaluate precision or reproduce the interpretation. The secondary outcome names likewise do not reveal their observed results.

Finally, planning calculations and observed results answer different questions. Planning illustrations rely on assumptions about design and effect; they do not turn a single-group pilot into a randomized comparison or establish observed power. Keeping those distinctions clear helps prevent descriptive findings from being overstated and makes the limits of a registry record explicit.

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 limitations arise from the information reported for this study. The trial was single group, open label, and had no comparator. Those design features prevent a like-for-like comparison and leave possible influences of disease course, prednisone tapering, other care, and event-reporting expectations unresolved. The registry record does not report a randomized allocation or a masked assessment process.

Although the primary endpoint is defined as the percentage of participants experiencing at least one adverse event during 52 weeks, the registry record does not report that percentage or an uncertainty interval. It reports serious and other adverse-event counts, but does not explain the relationship of those categories to the primary endpoint, whether categories overlap, or how event seriousness and treatment attribution were determined. The listed thrombocytopenia term has no further case-level context in the record.

The record does not report the results for relapse, erythrocyte sedimentation rate, or C reactive protein. It also does not report detailed eligibility criteria, baseline characteristics, outcome assessment schedules, analysis populations, missing-data handling, or inferential analyses. These omissions constrain assessment of who contributed data, how outcomes were measured, and how precise the reported counts are.

Enrollment of 15 is reported, but the registry information does not give a sample-size justification for the trial’s own design. Planning illustrations based on two-arm assumptions do not describe the actual single-group study and should not be mistaken for evidence of observed power. These limitations define what can be concluded from the registry record; they do not establish that unreported procedures or analyses were absent from the conduct of the study.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Baricitinib in Relapsing Giant Cell Arteritis — NCT03026504.
• Registry record last updated 2022-04-08; status last verified 2022-04.
• Results first posted 2022-04-08.
• 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 registry record describes a completed phase II, single-institution, open-label pilot study of baricitinib in relapsing giant cell arteritis. It reports enrollment of 15 participants and a single-group design. Participants received 4 milligrams of oral baricitinib daily for 52 weeks while prednisone was reduced according to a standardized tapering schedule.

The primary outcome was the percentage of participants with at least one adverse event during 52 weeks. Posted safety results include 1 participant with a serious adverse event among 15 at risk, 14 with other adverse events among 15 at risk, 0 deaths, and thrombocytopenia listed at 6.7% among serious adverse-event terms. Results for the listed secondary outcomes are not reported in the registry record.

No comparator was used, and the registry record does not report a primary-endpoint percentage, uncertainty interval, inferential analyses, or missing-data methods. The reported counts are descriptive and do not establish a comparative treatment effect or event causality.