Observational Non-Interventional Study With Enbrel (Etanercept) in Patients With Ankylosing Spondylitis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Observational Non-Interventional Study With Enbrel (Etanercept) in Patients With Ankylosing Spondylitis (NCT01188655), a registered phase not stated study. The primary outcome is Percentage of Participants Achieving BASDAI 40 Response at Week 24.

2. Clinical Question

The clinical question is descriptive rather than a randomized treatment comparison. The study was intended to document how Enbrel was prescribed and administered and to record outcomes among people with ankylosing spondylitis in routine practice. The primary endpoint focuses on whether participants met a specified threshold of improvement on the BASDAI by Week 24.

The registry lists 89 participants as enrolled. That figure is not necessarily the number with a recorded Week 24 assessment: the endpoint description says the number analyzed is the number of participants at the given time point, but the time-point-specific count is not reported in the registry record. The endpoint percentage itself is also not reported in the registry record.

Other listed outcomes include changes in BASDAI, BASFI and ASQoL, global assessments by participants and physicians, morning stiffness, and the presence or absence of enthesitis and peripheral arthritis. These measures broaden the description of outcomes, but the record does not provide numerical estimates for them. Without a control group suitable for comparison, results from this study would describe outcomes observed in the enrolled group rather than isolate the effect of Enbrel from other influences.

3. Trial Design

This is an observational, non-interventional study of Enbrel (etanercept) in patients with ankylosing spondylitis. The registry describes its purpose as documenting prescribing and administration practices and their relationship to patient outcomes in a real-life setting. It records one Treatment Group Enbrel; the group description contains no further details.

The record lists 89 participants as enrolled and gives the status as completed. The study start is recorded as 2008-05, and primary completion as 2010-03. Pfizer is listed as the sponsor. These registry entries identify the study's scope and status, but they do not establish how participants were selected, how treatment decisions were made, or how follow-up was managed.

Allocation is not stated, and the record does not describe a control group. It therefore does not support a like-for-like treatment comparison. In an observational study, treatment is not assigned through random allocation as part of the study; differences in participant characteristics, clinical decisions and follow-up can affect observed outcomes. These are general features to consider when interpreting observational evidence, not details of this study's procedures.

The primary endpoint is the percentage achieving a BASDAI 40 response at Week 24. Secondary outcomes include measures at Weeks 12 and 24, as well as measures for which the record does not specify a time point. Although 12 outcome measures and zero analyses are listed, numerical outcome findings are not reported in the registry record. The record also does not report a detailed protocol, eligibility criteria, the schedule of visits, or the methods used to account for differences among participants. Those omissions limit how fully the study's conduct and analysis can be evaluated.

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: Safety population: all participants who recieved at least one dose of study medication during the study period, n equals number of participants analyzed at the given time point

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 Percentage of Participants Achieving BASDAI 40 Response at Week 24, measured over Week 24.

The primary endpoint is the percentage of participants achieving a BASDAI 40 response at Week 24. BASDAI is a self-assessment tool for disease activity in ankylosing spondylitis. It uses six questions about discomfort, pain and fatigue, each answered on a visual analog scale from 0 to 10, where 0 means none and 10 means very severe. The responses are averaged to produce a final score ranging from 0 to 10.

A participant is classified as a responder if the BASDAI score decreases by 40 percent or more from baseline to the follow-up visit. This threshold turns a continuous score into a binary outcome: each assessed participant either meets the response definition or does not. The percentage then expresses the share of assessed participants who meet that definition.

A threshold-based response can be easier to interpret as a count or proportion than a mean score change, but it also compresses information. Participants just on opposite sides of the threshold are placed in different categories even if their score changes are similar. The underlying score changes can therefore add context to a response percentage.

The registry record describes the endpoint and its timing but does not report the observed Week 24 percentage, the number of responders, or the number assessed at that time point. The endpoint definition alone cannot establish what proportion met the response criterion.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is a binary response: participants are classified according to whether their BASDAI score decreased by 40 percent or more from baseline by Week 24. A percentage for such an outcome is based on a numerator, the number meeting the criterion, and a denominator, the number assessed for that endpoint. Both counts matter. A percentage without its denominator can conceal how much information supports the estimate, while a denominator that differs across visits can make time-point results less directly comparable.

What does the response threshold capture?

BASDAI measures disease activity through six self-assessment questions covering discomfort, pain and fatigue. Each uses a visual analog scale from 0 to 10, with 0 meaning none and 10 meaning very severe; the final score averages the individual assessments and ranges from 0 to 10. The endpoint converts change in that score into a responder classification using the stated decrease threshold. Dichotomizing a score can make a result straightforward to describe, but it discards detail about the size of changes and treats participants near the threshold as categorically different.

The registry record does not report the number of Week 24 responders, the number assessed, or the resulting percentage. It also does not report a confidence interval or a statistical test for the primary endpoint. No recalculation from posted summary statistics is possible from the information recorded for this endpoint.

How should uncertainty be considered?

As a general statistical concept, a confidence interval communicates uncertainty around an estimate. For a response percentage, that uncertainty depends in part on the number of observations contributing to the numerator and denominator. An interval does not remove uncertainty or account automatically for biases in how participants entered a study or how outcomes were recorded. No interval is reported for the primary endpoint in the registry record, so its statistical precision cannot be evaluated.

General methods for binary outcomes include estimating a proportion and attaching an interval, or using a regression model when adjustment for measured characteristics is justified and suitable data are available. The registry record does not state which, if any, such methods were used. It does not provide an adjusted estimate, a model specification, or information about covariates. The listed count of zero analyses means the record supplies no analysis results to evaluate.

Why does the study design matter?

This is an observational study, and allocation is not stated. The record describes an Enbrel treatment group but no like-for-like control comparison. In general, random allocation can help balance measured and unmeasured characteristics between treatment groups. Without such a comparison, differences in outcomes cannot be attributed to treatment alone. In observational research, adjustment can sometimes address measured differences, but it cannot guarantee control of unmeasured factors. The record does not report an adjustment strategy, so none should be assumed.

The endpoint description defines the population as people who received at least one dose, while the number analyzed depends on the time point. This makes the time-specific denominator important. The registry record does not state how missing Week 24 measurements were handled, whether participants with incomplete follow-up were excluded, or whether any imputation was used. These choices can affect a percentage, particularly if missingness is related to participant outcomes.

What do the planning assumptions represent?

Any sample-size figures associated with a planning exercise are illustrations rather than a record of the study's original design or observed power. The stated planning assumptions use a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is expressed as a fraction of the observed effect. These assumptions describe a hypothetical planning setup, not the design documented for this observational study. The record lists an Enbrel group and does not describe an equal-allocation, two-arm randomized comparison. Planning calculations cannot replace a reported endpoint estimate, and they do not show the probability that this completed study detected an effect.

More broadly, statistical methods should be interpreted in light of the endpoint, analysis population, design and missing-data handling. Here, the endpoint definition and some registry-level counts are available, but the numerical primary result and the analysis details are not reported in the registry record. As a result, the methods needed to assess the endpoint's estimated magnitude and precision cannot be verified from this record.

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("Etanercept")
n      <- c(67)
events <- c(56)
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  Etanercept  67  56  83.6  72.5  91.5  72.9  90.6  72.9  90.5

11. Multiplicity, Missing Data and Analysis Populations

The record lists 12 outcome measures, including the primary BASDAI 40 response and secondary measures of disease activity, function, quality of life, global assessment, morning stiffness, enthesitis and peripheral arthritis. It lists zero analyses. Numerical results and statistical tests for these outcomes are not reported in the registry record.

When a study examines multiple outcomes or multiple time points, the chance of obtaining at least one apparently notable result can increase if each is tested separately. General approaches include specifying a primary outcome in advance and adjusting or otherwise accounting for multiple comparisons. The registry record does not report a multiplicity strategy, a hierarchy among secondary outcomes, or whether any adjustment was applied. No such procedure should be inferred from the outcome list alone.

The primary endpoint is defined at Week 24, while several secondary measures are listed at Weeks 12 and 24. The record does not say whether all planned time points were analyzed or how results across time points were handled. It also does not report reasons for missing assessments, the amount of missing outcome data, or methods for addressing missingness. In general, analyses restricted to participants with observed measurements can be biased if missingness is related to outcomes or participant characteristics; the record does not establish whether that concern applies in this study.

The endpoint description defines the safety population as participants who received at least one dose, with the number analyzed at each time point. A time-specific analysis count is not reported in the registry record. Enrollment of 89 should not be treated as a substitute denominator for an endpoint with an unspecified assessed count. The record also does not report whether any other analysis populations were defined or how participants with incomplete data were handled.

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.

Most frequent non-serious adverse event terms

For the Etanercept group, the registry reports 89 at risk for the serious-event count and 0 affected. It reports 89 at risk for the other-event count and 3 affected. These are the safety figures recorded; the registry record does not provide further detail about the event definitions in these fields.

The record does not list any serious-event terms. The deaths value is not reported in the registry record. No further event descriptions, timing, severity breakdown, or analysis details are available in these fields. The counts therefore provide limited descriptive information and should not be read as a complete account of safety during the study.

These figures do not establish whether an event was caused by Enbrel. In general, an event observed during treatment is not necessarily attributable to the treatment, particularly in an observational study without a control comparison. The safety counts also do not provide a basis for comparing risk between treatments. They should be interpreted as the registry's reported counts, not as evidence for or against a causal relationship.

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

The registry record establishes that an observational study of Enbrel in patients with ankylosing spondylitis was completed, with 89 participants enrolled. Its stated purpose was to document prescribing and administration practices and patient outcomes in a real-life setting. The primary outcome was defined as the percentage achieving a BASDAI 40 response at Week 24, where response means a decrease of 40 percent or more from baseline.

The record does not report the numerical result for that primary endpoint, the number of participants assessed at Week 24, or a measure of uncertainty. It therefore does not show what proportion met the response definition or how precisely that proportion was estimated. Listed secondary outcomes likewise have no numerical findings in the registry record.

Even if an outcome estimate were available, an observational description without a like-for-like control group would not by itself isolate a treatment effect. Differences in who received treatment, their clinical circumstances, and how outcomes were observed can influence the results. Allocation is not stated, and the record does not report adjustment methods that might address measured differences.

The listed safety counts are limited: the record gives 0 affected in the serious-event count and 3 affected in the other-event count, each with 89 at risk. It does not report the deaths value or serious-event terms. These fields do not establish causality or support a comparison with another treatment.

Accordingly, the record is informative about the study's purpose, endpoint definition, listed outcomes and some safety counts. It does not support a quantitative conclusion about the primary response outcome, its precision, or a causal effect of treatment. Missing outcome and analysis details should be treated as unreported rather than interpreted as zero or as evidence of no change.

14. Why This Trial Matters Statistically

This study is statistically relevant because it illustrates the distinction between documenting outcomes in routine practice and estimating a treatment effect through a controlled comparison. The stated aim was to record prescribing and administration practices and outcomes in a real-life setting. That type of description can address what was observed in a treated group, but it does not by itself show how outcomes would have differed under another treatment or without treatment.

The primary endpoint uses a defined responder threshold on BASDAI, a self-assessment measure of disease activity. A threshold-based percentage is easy to communicate, while retaining the underlying score and its change can provide additional detail. To evaluate the response percentage, readers need both the number meeting the threshold and the number assessed. Neither the Week 24 numerator nor the denominator is reported in the registry record.

The registry lists several additional outcomes and time points, underscoring why a clear analysis plan matters. Multiple outcomes can complicate interpretation if the selection of findings is not prespecified or if repeated testing is not considered. The record does not report a multiplicity strategy or numerical analyses, so the extent to which those issues were addressed cannot be assessed.

The safety entries also demonstrate why counts need context. The record reports counts and numbers at risk, but supplies no event terms for serious events and no deaths value. These limited entries cannot establish causation or comparative safety. Overall, the record makes the intended descriptive question clear, while the absent endpoint estimates and analysis details constrain statistical interpretation.

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.

Important limitations are specific to the information recorded for this study. The primary endpoint is defined, but its Week 24 value, responder count and time-point denominator are not reported in the registry record. The listed enrollment of 89 does not establish how many participants contributed data to that endpoint. Consequently, neither the size nor precision of the primary response estimate can be assessed.

The study is observational, and allocation is not stated. The record describes an Enbrel group but no suitable control comparison. This limits causal interpretation: outcomes in the treated group cannot by themselves distinguish treatment effects from other influences. The registry record also does not report an adjustment strategy or participant characteristics that would help evaluate potential differences in who received treatment.

The record lists 12 outcome measures and zero analyses. It does not provide numerical results for the primary or secondary outcomes, statistical tests, confidence intervals, or a multiplicity plan. Missing-data methods and the amount of missing outcome information are also not reported. These gaps prevent assessment of how robust the results would be to incomplete follow-up or analytic choices.

The group description is empty, and details such as eligibility criteria, visit schedules, treatment duration and outcome-assessment procedures are not reported in the registry record. Safety reporting is also limited: serious-event terms are not listed, and the deaths value is not reported. These are limits of the registry information and should not be replaced by assumptions about what the full study may have recorded.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Observational Non-Interventional Study With Enbrel (Etanercept) in Patients With Ankylosing Spondylitis — NCT01188655.
• Registry record last updated 2011-09-12; status last verified 2011-09.
• Results first posted 2011-04-26.
• 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 observational, non-interventional study examined Enbrel (etanercept) in patients with ankylosing spondylitis. Pfizer is listed as sponsor. The registry records 89 participants enrolled, a start of 2008-05 and primary completion in 2010-03.

The primary endpoint is the percentage achieving a BASDAI 40 response at Week 24, defined as a decrease of 40 percent or more from baseline. The registry lists 12 outcome measures and zero analyses, but does not report numerical efficacy findings or the Week 24 analysis denominator.

For the Etanercept group, the record reports 0 affected in the serious-event count and 3 affected in the other-event count, with 89 at risk for each. Serious-event terms and the deaths value are not reported in the registry record. Allocation is not stated, and no like-for-like control comparison is described.