PREDICT-SpA - French Epidemiological Study of the Evaluation of the Impact of Fibromyalgia in the TNF Alpha Treatment Effect in Axial Spondyloarthritis in Both Anti-TNF naïve and - Experienced Patients: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for PREDICT-SpA - French Epidemiological Study of the Evaluation of the Impact of Fibromyalgia in the TNF Alpha Treatment Effect in Axial Spondyloarthritis in Both Anti-TNF naïve and - Experienced Patients (NCT03039088), a registered phase not stated study. The primary outcome is To Evaluate the Presence of Fibromyalgia (Defined by a FIRST Questionnaire >= 5/6) as a Predisposing Factor for Lower Treatment Response Rates to TNF Alpha Blockers.

2. Clinical Question

3. Trial Design

PREDICT-SpA is described as a prospective observational national study conducted in France. It examined people with axial spondyloarthritis who were starting a TNF alpha blocker in routine care. The study included both anti-TNF-naïve and anti-TNF-experienced patients. The stated recruitment objective was 500 patients; the registry lists enrollment as 527. The relationship between that enrollment figure and the patients included in the outcome and safety groups is not reported in the registry record.

The study description specifies two visits: baseline and 12 weeks after TNF alpha blocker initiation. The primary endpoint timeframe is also given as 12 weeks after initiation. The comparison was by fibromyalgia status, with one group labeled fibromyalgia patients and the other not fibromyalgia patients. Fibromyalgia was defined using a FIRST questionnaire threshold of >= 5/6. The registry does not describe random allocation, and it explicitly identifies the comparison as non-randomized. Treatment was not assigned by the study, so the groups should not be read as randomized treatment arms or as a like-for-like controlled comparison.

The sponsor is Association de Recherche Clinique en Rhumatologie. The recorded study dates are 2014-10-02 for study start and 2016-10-04 for primary completion, and the status is completed. The registry lists follow-up after treatment initiation as the intervention. It does not report a more detailed protocol, the method used to select participants, or the handling of patients who did not complete follow-up. Those details are not reported in the registry record.

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 To Evaluate the Presence of Fibromyalgia (Defined by a FIRST Questionnaire >= 5/6) as a Predisposing Factor for Lower Treatment Response Rates to TNF Alpha Blockers, measured over At 12 weeks after TNF alpha blockers initiation.

The primary endpoint is described as the difference in BASDAI50 response at week 12 between patients with fibromyalgia and patients without fibromyalgia. It is framed as a participant-level response outcome and is intended to address whether fibromyalgia status is associated with treatment response after TNF alpha blocker initiation. Fibromyalgia classification used a FIRST questionnaire score of >= 5/6.

In general, a defined response endpoint gives a study a prespecified clinical outcome to compare across groups at a particular follow-up time. A binary response measure classifies each participant as meeting or not meeting the response definition, and group response rates can then be compared. The registry record does not give the operational definition of BASDAI50 beyond its name, nor does it report the number of participants meeting the endpoint in either group. It also does not provide an estimated difference or a confidence interval. The clinical and statistical meaning of the observed contrast therefore cannot be assessed from the reported primary results, because those results are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does the primary comparison represent?

The primary question concerns the difference in BASDAI50 response at week 12 between patients with fibromyalgia and patients without fibromyalgia. In general, a group difference is a contrast between the outcome summaries for the groups being compared. For a binary response, that contrast can be expressed using response proportions, but the registry does not report either group's response count or response proportion, or a numerical difference between them. No independent calculation of the effect is possible from the record.

The endpoint is a participant-level outcome, and the registry labels its parameter as a number of participants. That label does not supply the actual response counts. The record also does not give further details about how BASDAI50 was operationalized, how the outcome was collected, or whether any modified endpoint rules were used. These details are not reported in the registry record.

What can a confidence interval tell a reader?

In general, a confidence interval describes the range of effect estimates compatible with the observed data under the method used to calculate it. Its width conveys precision: wider intervals indicate less precise estimation, while narrower intervals indicate greater precision. A confidence interval is not a guarantee that the true effect lies within its endpoints, and it does not resolve bias from the study design. No confidence interval for the primary comparison is reported in the registry record, so the precision of the estimated difference cannot be assessed.

Why does the observational design matter?

In general, randomization can balance measured and unmeasured characteristics between assigned groups on average. Here, the groups were defined by fibromyalgia status, not randomized assignment. Differences in patient characteristics, treatment history, or clinical circumstances could therefore be related to both group membership and response. The study includes anti-TNF-naïve and previously exposed patients, but the registry does not describe how those histories were handled in the primary analysis. It also does not report adjusted estimates, covariates, or a statistical model. The comparison should therefore be understood as observational, and causal interpretation is not supported by the record alone.

What is over-dispersion, and is it relevant?

In general, over-dispersion occurs when outcome variability is greater than a statistical model assumes. It can make standard errors too small if a model does not account for the extra variability. Over-dispersion is relevant to some count or clustered-data analyses, but the registry describes the primary endpoint as a participant response and does not report a model or an over-dispersion assessment. There is no basis in the record to say whether it was considered or whether it would affect the primary comparison.

How should planning calculations be read?

In general, sample-size planning illustrates how many participants might be needed under specified assumptions; it does not measure the power achieved after a study is completed. The planning assumptions associated with this record specify a two-sided significance level of 0.05, equal allocation between groups, a normal approximation, and an effect to detect expressed as a stated fraction of the observed effect. The assumptions describe a planning illustration, not the study's own design rationale. The record does not report the trial's sample-size justification, and any planning illustration must not be interpreted as observed power or as evidence that the study detected an effect.

The registry does not state which method was used to estimate the primary effect, calculate uncertainty, or test a hypothesis. It also does not report whether an interim analysis was planned or conducted. Those methods are not reported in the registry record. As a result, no model-specific assumptions or inferential procedures can be attributed to the study from this entry.

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("Fibromyalgia Patients", "Not Fibromyalgia Patients")
n      <- c(192, 316)
events <- c(87, 171)
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  Fibromyalgia Patients  192  87  45.3  38.1  52.6  38.4  52.4  38.4  52.4
ARM  Not Fibromyalgia Patients  316  171  54.1  48.4  59.7  48.6  59.5  48.6  59.5

11. Multiplicity, Missing Data and Analysis Populations

The registry lists four outcome measures and zero analyses. It names the primary outcome as the difference in BASDAI50 response at week 12 between the fibromyalgia and non-fibromyalgia groups. The listed secondary outcomes concern doctors' versus patients' reported outcomes in decisions to initiate or switch anti-TNF therapy, the percentage of patients with fibromyalgia, and concordance between current recommendations and daily practice. Numerical results for these outcomes are not reported in the registry record.

When a study assesses multiple outcomes or performs multiple comparisons, the chance of at least one apparently unusual result can increase. In general, multiplicity methods are used to manage or describe that issue, but no multiplicity plan or adjustment is reported in the registry record. The record also does not specify whether the primary comparison was the only planned analysis, whether subgroup analyses were planned, or how any additional comparisons were to be interpreted.

Missing-data handling is not reported in the registry record. The entry does not state how many participants had a week-12 assessment, whether outcome data were missing, or how missing responses were treated. Analysis populations are also not described: the record does not specify an intention-to-treat population, a per-protocol population, or another population for the primary endpoint. The enrollment figure and the adverse-event group counts do not establish the primary endpoint denominator. Without outcome availability, analysis-population definitions, and missing-data methods, it is not possible to judge whether the reported groups represent all enrolled participants or to assess potential bias from incomplete follow-up.

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 safety summary lists 202 people at risk in the fibromyalgia group and 324 in the group without fibromyalgia. For serious adverse events, it records zero affected in each group; for other adverse events, it also records zero affected in each group. These are the registry's listed counts. The deaths field is null for both groups, so deaths are not reported in the registry record.

These figures should be read as registry entries, not as evidence that no adverse events occurred during the study. The record does not provide event descriptions, timing, severity beyond the serious-versus-other categories, ascertainment procedures, or an explanation of whether the zero counts reflect complete reporting. It also does not state how these safety groups relate to the population assessed for the primary outcome. Because the study is observational and the groups are defined by fibromyalgia status, the safety counts do not constitute a randomized safety comparison. No causal conclusion about treatment-related risk can be drawn from these counts alone.

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

The record establishes that PREDICT-SpA was designed to examine whether fibromyalgia status was associated with BASDAI50 response at 12 weeks after TNF alpha blocker initiation among people with axial spondyloarthritis. It specifies a prospective observational approach, the fibromyalgia classification threshold, the two group labels, and the primary timeframe. It also records enrollment and describes the intended recruitment objective. These details help readers understand the research question and the setting of the comparison.

The registry record does not report the primary response counts, response rates, estimated group difference, confidence interval, or p-value. Consequently, it does not show whether one group had a higher or lower response rate, how large any difference was, or how precisely it was estimated. The completed status does not fill this gap. Secondary outcomes are listed, but their numerical results are not reported in the registry record either.

Even if an outcome contrast were available, the non-randomized comparison would require cautious interpretation. Patients were grouped by fibromyalgia status, and the registry explicitly says this is not a like-for-like control comparison. In general, characteristics associated with fibromyalgia status or treatment history can also be associated with response. The record does not report adjustment methods that would address such differences, and an observational association would not by itself demonstrate a causal effect of fibromyalgia.

The posted safety counts record zero serious and zero other adverse events in each listed group, with deaths not reported in the registry record. They do not provide enough detail to establish the completeness of safety ascertainment or to compare risks causally. The appropriate conclusion is limited: the registry describes a study intended to assess response and related outcomes, but the results needed to judge those questions are not reported in the registry record.

14. Why This Trial Matters Statistically

This study addresses a statistical challenge common in clinical research: treatment response may be evaluated across groups defined by a coexisting condition rather than by randomized assignment. The question is whether fibromyalgia status is associated with the response observed after TNF alpha blocker initiation in axial spondyloarthritis. Because the classification is observational, the analysis must distinguish a group association from a causal effect. That distinction is central to interpreting the design.

The study also brings together patients who were anti-TNF-naïve and patients who had prior exposure. Treatment history could be relevant to the comparison, but the registry does not report how it was incorporated into the analysis. This illustrates why the statistical analysis plan, population definitions, and adjustment methods matter: without them, readers cannot determine how clinical heterogeneity was handled.

At the same time, statistical interpretation depends on reported effect estimates and uncertainty, not simply on a study's objective, enrollment, or completion status. The registry specifies the primary endpoint and timeframe but does not report the outcome results. It is therefore not possible to assess the magnitude or precision of the primary comparison. The missing numerical results limit what can be learned from the registry entry, even though its design description identifies a relevant research question.

The record is also a useful reminder that safety counts and efficacy outcomes answer different questions. The listed adverse-event counts do not substitute for a treatment-response estimate, and neither set of counts can support causal conclusions without suitable design and analysis. Clear reporting of denominators, outcome availability, missing-data handling, and estimates with uncertainty would be important for interpreting this type of observational comparison.

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.

The main limitation for interpretation is that the primary endpoint results are not reported in the registry record. There are no response counts or rates, estimated difference, confidence interval, or p-value. The record therefore does not permit an assessment of direction, magnitude, or precision. Although the study is marked completed, completion status alone does not provide outcome evidence.

The comparison is observational and non-randomized. Fibromyalgia status defines the groups, and the record says they are not a like-for-like control comparison. Potential differences between groups may influence the observed response contrast. The registry does not report adjusted analyses, covariates, subgroup results, or the handling of anti-TNF-naïve versus previously exposed patients. The extent to which these factors were considered is not reported in the registry record.

Further limitations are the absence of information about missing outcome data, analysis populations, endpoint ascertainment, and the operational definition of BASDAI50 beyond its name. The registry does not explain how the listed enrollment relates to the numbers at risk in the safety summaries or to the primary endpoint population. The safety entries list zero affected in both groups for serious and other events, but deaths are not reported and details of ascertainment are absent. Finally, the record does not state the multiplicity approach, interim-analysis procedures, or full statistical plan. These omissions restrict reproducibility and make it difficult to evaluate the reliability of any potential comparison.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: PREDICT-SpA - French Epidemiological Study of the Evaluation of the Impact of Fibromyalgia in the TNF Alpha Treatment Effect in Axial Spondyloarthritis in Both Anti-TNF naïve and - Experienced Patients — NCT03039088.
• Registry record last updated 2018-09-19; status last verified 2018-01.
• Results first posted 2018-09-19.
• 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

PREDICT-SpA is a completed prospective observational study in France of patients with axial spondyloarthritis initiating a TNF alpha blocker. The study description includes anti-TNF-naïve and previously exposed patients and specifies baseline and 12-week visits. Fibromyalgia status was defined using a FIRST questionnaire threshold of >= 5/6. The primary question was whether BASDAI50 response at week 12 differed by fibromyalgia status.

The registry lists enrollment as 527 and gives a recruitment objective of 500. It lists 202 and 324 people at risk in the two safety groups, with zero serious and zero other adverse events recorded in each. Deaths are not reported in the registry record. Primary response results, statistical analyses, missing-data methods, and analysis populations are not reported in the registry record. The entry therefore describes the study question and design but does not provide enough outcome information to evaluate the primary comparison.