A Study of Ixekizumab (LY2439821) in Chinese Participants With Radiographic Axial Spondyloarthritis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study of Ixekizumab (LY2439821) in Chinese Participants With Radiographic Axial Spondyloarthritis (NCT04285229), a randomized phase 3 study. The primary outcome is Percentage of Participants Achieving an Assessment of Spondyloarthritis International Society 40 (ASAS40) Response in Biological Disease-modifying Antirheumatic Drug (bDMARD)-naïve Participants.

2. Clinical Question

The clinical question is about a defined short-term response in a particular participant subgroup, not about every possible effect of treatment or the longer-term results. The study also listed other efficacy outcomes, including ASAS20, disease activity, function, imaging, and health-related quality of life. Their presence broadens the outcomes assessed but does not change the primary question.

3. Trial Design

This was a phase 3, randomized, double-blind, parallel-group, placebo-controlled study. The registry record gives an enrollment of 147 and describes the study as evaluating ixekizumab efficacy and safety in Chinese participants with radiographic axial spondyloarthritis. The official title describes a 16-week study followed by long-term evaluation. The registry status is completed.

During the double-blind period, the intervention group received ixekizumab and the comparator group received placebo. The ixekizumab schedule began with 160 mg and continued with 80 mg once every four weeks by subcutaneous injection. The placebo arm description specifies placebo every four weeks during the double-blind period. In the extension description, participants initially assigned to placebo switched to ixekizumab; the record also describes continued ixekizumab for participants who had received it earlier.

Randomization and double masking are features of the design intended to support a balanced comparison and reduce the influence of expectations on trial conduct and assessment. In general, a parallel-group design assigns participants to a group and compares outcomes between groups over the study period. These design features do not, by themselves, reveal details such as the randomization procedure or who was masked; those details are not reported in the registry record.

The primary endpoint was assessed at week 16 and focused on ASAS40 among biological disease-modifying antirheumatic drug-naïve participants with endpoint data. The record also lists a broader ASAS40 endpoint and multiple other secondary outcomes. The registry record does not report the original sample-size justification, the planned statistical analysis details beyond the listed analysis, or whether interim analyses were planned.

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.

Double-Blind Treatment Period

Reasons for not completing this period:

Extended Treatment Period

Reasons for not completing this period:

Follow-up Period

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: All randomized participants from bDMARD-naïve who had data for ASAS40.

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: All randomized participants

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Participants Achieving an Assessment of Spondyloarthritis International Society 40 (ASAS40) Response in Biological Disease-modifying Antirheumatic Drug (bDMARD)-naïve Participants, measured over Week 16.

The primary endpoint is the percentage of biological disease-modifying antirheumatic drug-naïve participants achieving an ASAS40 response at week 16. ASAS40 is a composite response definition. It requires improvement from baseline of at least 40% and an absolute improvement of at least 2 units in at least three of four domains, with no worsening in the remaining domain.

The four domains are patient global assessment, spinal pain, physical function measured using BASFI, and inflammation measured using questions from BASDAI. Each domain uses a scale from 0 to 10, with higher scores indicating more activity, pain, difficulty, or severity as specified in the endpoint description. A participant therefore has to meet the response threshold across multiple aspects of the condition rather than on one measure alone.

In general, a composite endpoint can capture change across several clinically relevant dimensions in a single response definition. It can also be harder to interpret than a single measurement, because the overall response does not show which individual domain changed most. ASAS40 is used in the registry as the primary measure of response at week 16; the registry record does not report a separate rationale for selecting this endpoint or further details about how missing domain measurements were handled.

7. Results Posted in the Registry

• Ixekizumab 80mg Q4W: 40.9% (27/66) versus 7.8% (5/64) on control; risk difference 33.1 percentage points (95% CI 19.5 to 46.7), risk ratio 5.24 (2.15–12.75); unadjusted two-proportion z-test p = <0.001.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Percentage of Participants Achieving an ASAS40 Response

• Endpoint type: Binary: the percentage of participants with the event (counts rebuilt from the posted percentages and group sizes).
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Ixekizumab 80mg Q4W: 37.8% (28/74) versus 8.2% (6/73) on control; risk difference 29.6 percentage points (95% CI 16.9 to 42.3), risk ratio 4.60 (2.03–10.46); unadjusted two-proportion z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the proportion with the event is statistically higher for Ixekizumab 80mg Q4W than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Percentage of Participants Achieving an ASAS20 Response

• Endpoint type: Binary: the percentage of participants with the event (counts rebuilt from the posted percentages and group sizes).
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Ixekizumab 80mg Q4W: 59.5% (44/74) versus 35.6% (26/73) on control; risk difference 23.8 percentage points (95% CI 8.2 to 39.5), risk ratio 1.67 (1.16–2.40); unadjusted two-proportion z-test p = 0.004.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the proportion with the event is statistically higher for Ixekizumab 80mg Q4W than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Change From Baseline in Ankylosing Spondylitis Disease Activity Score (ASDAS)

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard errors.
• Result:
  • Ixekizumab 80mg Q4W: mean -1.33 versus -0.19 on control; difference -1.14 (95% CI -1.42 to -0.86), standardized effect d = -1.31; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for Ixekizumab 80mg Q4W than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The registry lists a broad set of secondary outcomes: ASAS40 and ASAS20 response, disease activity measured by ASDAS, BASDAI response, physical function measured by BASFI, spinal MRI SPARCC score, and physical and mental component scores from SF-36. The posted secondary results include binary response outcomes and continuous changes from baseline. Across the reported comparisons, the pattern is generally consistent with the primary endpoint: the ixekizumab group has higher response percentages for the listed response outcomes and larger decreases in the reported ASDAS measure than the placebo group at week 16.

This broad pattern provides context for the primary ASAS40 result because the other outcomes assess related but distinct aspects of response, such as disease activity, function, imaging, and health-related quality of life. They do not replicate the primary endpoint exactly, and they do not establish that every domain changed in the same way. The registry record lists 16 secondary outcomes as posted, but detailed interpretations should remain tied to each outcome’s own definition, scale, analysis population, and time point.

In general, multiple secondary outcomes create a multiplicity concern: the more statistical tests conducted, the more likely at least one may appear statistically significant by chance if all are interpreted as confirmatory without adjustment. The registry record does not report whether multiplicity adjustments were planned or applied. Therefore, unadjusted secondary results carry less weight as confirmatory evidence than a prespecified primary analysis. They are best read as supportive or exploratory context unless the analysis plan establishes otherwise, and that plan is not reported in the registry record.

The secondary endpoints should not be combined into a single overall effect, and their results should not be used to infer unreported outcomes. Their value is in showing whether different measurements tell a broadly coherent story, while acknowledging that the available registry information does not establish the hierarchy or inferential status of each secondary test.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Percentage of Participants Achieving an ASAS40 Response
• Percentage of Participants Achieving an ASAS20 Response
• Change From Baseline in Ankylosing Spondylitis Disease Activity Score (ASDAS)
• Change From Baseline in Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) Response
• Change From Baseline in Bath Ankylosing Spondylitis Functional Index (BASFI)
• Change From Baseline in Magnetic Resonance Imaging (MRI) of the Spine (Spondyloarthritis Research Consortium of Canada [SPARCC] Score)
• Change From Baseline in 36-Item Short Form Health Survey (SF-36) Physical Component Summary (PCS) Score
• Change From Baseline in 36-Item SF-36 Mental Component Summary (MCS) Score

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is binary at the participant level: each participant either meets the ASAS40 response definition at week 16 or does not. The registry presents the result as a percentage of participants. The recalculation also uses the posted response counts and group sizes to describe the unadjusted contrast. The registry record reports a logistic regression analysis for its own primary comparison.

What does a response percentage describe?

In general, a response percentage is the share of participants in a group who met the endpoint definition. It is a direct description of the observed group data, but it does not by itself quantify how much uncertainty surrounds that percentage or the contrast between groups. The reported percentages are 7.8% for placebo and 40.9% for ixekizumab 80mg Q4W in the primary population. The corresponding group sizes are 64 and 66. The endpoint’s population restriction matters: these figures are for biological disease-modifying antirheumatic drug-naïve participants with ASAS40 data.

What is the risk difference?

In general, a risk difference subtracts one group’s event probability from the other group’s event probability. It is an absolute measure, expressed on the probability scale. The unadjusted recalculation gives a risk difference of 0.331 for ixekizumab relative to placebo. The interval for this recalculation stays above zero. This measure describes the observed gap in response proportions; it is not the same quantity as an odds ratio. The risk difference is a simple comparison of the posted summary data and is not a replacement for the registry’s reported analysis.

What is an odds ratio?

In general, an odds ratio compares the odds of an outcome between groups. Odds and probabilities are related but are not the same scale, so an odds ratio should not be read as a risk difference or as a direct multiplication of response percentages. The registry reports a logistic regression analysis with an odds ratio of 7.64 for the primary comparison. Its 95% confidence interval is 2.68 to 21.76, and the reported p-value is <0.001. The registry record identifies logistic regression but does not report the model’s covariates or other implementation details.

The recalculated comparison and the reported analysis answer related but not identical statistical questions. The recalculation is an unadjusted comparison on the risk-difference scale, while the registry analysis reports a logistic-regression odds ratio. Their magnitudes should not be compared as though they were estimates on a common scale. Both describe a contrast between the same primary groups, but only the registry analysis represents the sponsor’s reported model-based result.

How should the p-value be read?

In general, a p-value measures how unusual data at least as extreme as those observed would be under a specified null hypothesis and model. A small p-value is evidence against that null model under the analysis assumptions. It does not tell the reader the probability that the treatment effect is real, the probability that the result will replicate, or whether the magnitude is important. The registry’s primary analysis reports p <0.001; the recalculated unadjusted comparison also reports p <0.001. These values belong to their respective analyses.

Hypothesis tests and confidence intervals are related ways to describe uncertainty, but each depends on the statistical model and estimand. A confidence interval includes a range of values compatible with the data and method at its stated confidence level. The registry reports a 95% interval for the odds ratio. The unadjusted recalculation reports an interval for the risk difference. Their scales and methods differ, so they should be interpreted separately.

What is the role of the secondary continuous outcome?

The registry also reports change from baseline in ASDAS at week 16 as a least-squares mean. The posted values are -0.19 for placebo and -1.33 for ixekizumab 80mg Q4W, with standard errors of 0.103 and 0.1. The registry’s reported mixed models analysis gives a least-squares mean difference of -1.14, a 95% confidence interval from -1.38 to -0.90, and p <0.001. This is a continuous outcome, unlike the binary ASAS40 response. In general, a mean difference compares average changes on the outcome’s measurement scale. The registry identifies a mixed models analysis, but further model details are not reported in the registry record.

The recalculated methods are not the trial’s full statistical plan. The original sample-size justification, detailed missing-data approach, covariate specifications, and any interim analyses are not reported in the registry record. Those absences limit the ability to reconstruct every analytic decision from the posted summaries.

11. Confidence Intervals and Precision

Precision describes how much uncertainty remains around an estimated effect. The registry reports the primary result as an odds ratio of 7.64, with a 95% confidence interval from 2.68 to 21.76. The interval is on the odds-ratio scale and does not directly describe the range of plausible risk differences. It spans a substantial range of odds-ratio values, so the point estimate should not be treated as an exact description of the underlying contrast.

In general, a confidence interval is generated by a statistical method and reflects uncertainty under that method’s assumptions. A 95% confidence interval is not a guarantee that a particular interval contains the true value. It is a procedure that, under its assumptions and repeated use, would cover the target value at the stated rate. The interval also does not incorporate every possible source of uncertainty, such as limitations in the trial record or differences between the study population and other populations.

The unadjusted recalculation uses the posted primary response summaries and reports a risk difference of 0.331. Its interval remains above zero. That interval uses the absolute probability scale, unlike the sponsor’s odds-ratio interval. The result is therefore evidence of a positive absolute contrast in the posted sample, but precision should be considered alongside the endpoint, subgroup, and analysis method. The recalculated interval endpoints are not repeated numerically because they are reported with more than three decimal places.

The reported group sizes for the primary analysis are 64 and 66. The record does not state the number of participants with missing endpoint data relative to all randomized participants in the primary subgroup, or how such missing data were handled. As a result, the precision figures cannot resolve uncertainty arising from unreported missing-data procedures.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

Sample-size illustrations based on an observed effect are planning exercises, not a reconstruction of the trial’s original design. For non-time-to-event outcomes such as these, the figures refer to participants per arm, not total events. The assumptions listed for the illustrations are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. Each illustration uses a stated fraction of the observed effect as the effect to detect.

The 80% power column describes the number of participants per arm in an illustrative design that would have an 80% chance of detecting the specified effect under those assumptions, if that effect and the assumptions were correct. The 90% power column makes the corresponding illustration for a 90% chance. These are planning probabilities under a model, not guarantees about the results of a future study. The trial’s own original sample-size assumptions and justification are not reported in the registry record.

The rows for 100%, 75%, and 50% of the observed effect show how the illustrative requirements change when the target effect is smaller than the observed one. Smaller effects generally require more participants to detect with the same power and significance level. For example, for the primary comparison, the illustration using 100% of the observed effect lists 26 participants per arm for 80% power and 34 participants per arm for 90% power; the illustration using 50% lists 77 and 102 participants per arm, respectively.

These figures are not observed power. Observed power would not provide a useful substitute for the confidence interval and the uncertainty in the estimated effect. The planning values are sensitive to the observed effect used as their starting point, so they should be read as conditional illustrations rather than as evidence that the completed trial was designed with those sample sizes or assumptions.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.078; treatment proportion p₁ = 0.409; average p̄ = 0.244.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.6071 = 1.1898.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.5601 = 0.4714.
4. n = (1.1898 + 0.4714)² / (0.3310)² = 25.2, rounded up to 26 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
p0 <- 0.078125                          # control proportion
p1 <- 0.409090909090909                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(4285229)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 26 (80% power), 34 (90% power)
 75% of observed effect: n per arm = 40 (80% power), 53 (90% power)
 50% of observed effect: n per arm = 77 (80% power), 102 (90% power)
power.prop.test: 25.2 
Simulated power at n = 26 per arm: 0.846 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Analyses Reported by the Sponsor

The registry’s reported primary analysis is a logistic regression estimate: odds ratio 7.64, with a 95% confidence interval from 2.68 to 21.76 and p <0.001. The recalculation is an unadjusted comparison of the posted response summaries on the risk-difference scale, with an estimate of 0.331 and p <0.001. An odds ratio and a risk difference use different scales, so the two estimates are not expected to have the same numerical value.

The reported odds ratio is the sponsor’s own analysis as recorded in the registry and should be distinguished from the unadjusted recalculation. The methods also differ: the registry identifies logistic regression, while the recalculation uses posted group summaries without model adjustment. The registry record does not report the logistic model’s covariates or additional specifications, so the reported estimate cannot be fully reconstructed from the record alone.

The two analyses point in the same direction and both report p <0.001, but their agreement does not make them interchangeable. For interpretation of the trial’s own analysis, the registry’s reported analysis takes precedence. The recalculation is useful as a transparent, simple description of the posted data, with the caveat that it answers a different statistical question from the regression odds ratio.

15. Multiplicity, Missing Data and Analysis Populations

The registry record identifies a primary endpoint and lists many secondary outcomes, but it does not report a multiplicity-control strategy. Multiplicity arises when multiple outcomes, time points, or statistical comparisons are tested. In general, if many tests are interpreted as independent opportunities to declare a result, the chance of at least one apparently positive result can increase. Prespecified testing hierarchies or statistical adjustments can address this concern, but whether either was used is not reported in the registry record.

The primary result should therefore be distinguished from the secondary findings. The primary endpoint is explicitly identified as ASAS40 at week 16 in biological disease-modifying antirheumatic drug-naïve participants with endpoint data. The record also posts a broader ASAS40 outcome and other secondary measures. Without a reported analysis plan describing endpoint hierarchy and multiplicity handling, the degree to which secondary p-values were intended to support confirmatory conclusions is unclear.

Missing-data handling is also not reported in the registry record. The primary population definition includes participants with ASAS40 data, but the record does not explain how participants without endpoint data were treated, whether any imputation was used, or what assumptions underlay the analysis. It is therefore not possible to assess the sensitivity of the result to missing outcomes from the registry summaries alone.

The primary analysis is restricted to biological disease-modifying antirheumatic drug-naïve participants with data. The broader ASAS40 analysis uses different group sizes, 73 for placebo and 74 for ixekizumab. The record does not fully describe the relationship between these analysis populations or provide a detailed participant flow for the endpoint. The terms used to describe the primary population should be retained when interpreting its percentages rather than assuming that they represent every randomized participant.

The registry record identifies logistic regression for the sponsor’s primary analysis but does not report the model covariates, detailed analysis population rules beyond the stated endpoint population, or other model specifications. It also does not report the trial’s original sample-size justification or whether interim analyses were planned. These omissions limit independent assessment of the full prespecified statistical strategy.

16. 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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: male genital tract tuberculosis (1.6%), auricular haematoma (1.4%), brain contusion (1.4%), hand fracture (1.4%), spinal osteoarthritis (1.4%).

The registry lists serious adverse event counts and participants at risk for several treatment-period groupings. During the listed placebo group, 1 serious adverse event was reported among 73 participants at risk; the ixekizumab 80mg Q4W group lists 2 among 74. In the extended treatment period groupings, the placebo/ixekizumab group lists 6 among 70, and the ixekizumab/ixekizumab group lists 4 among 72. The follow-up groupings list 0 among 1 for placebo and 1 among 135 for ixekizumab. No deaths are listed in any of these groups.

These figures are counts for the registry’s stated groupings and periods. They should not be combined or interpreted as directly comparable rates without more information about exposure time, participant movement between periods, and the safety analysis definitions. The record also lists other adverse events, but a serious adverse event is a distinct category and should not be conflated with all adverse events.

In general, safety counts describe events recorded under the study’s definitions; they do not establish whether an event was caused by treatment. The registry record does not provide enough detail to assess causality, event timing, or comparative risk over equivalent exposure periods. The posted figures are descriptive and should be read in the context of their separate treatment and follow-up groupings.

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

The primary result describes the percentage meeting a defined ASAS40 response at week 16 among biological disease-modifying antirheumatic drug-naïve participants with endpoint data. The registry reports 7.8% in the placebo group and 40.9% in the ixekizumab 80mg Q4W group. The recalculated absolute contrast is 0.331, while the registry’s own logistic regression analysis reports an odds ratio of 7.64 with a 95% confidence interval from 2.68 to 21.76 and p <0.001.

In general, a statistically detectable group contrast is not the same as a complete account of its clinical meaning. The primary endpoint combines improvements across several domains, and an overall response does not reveal which domain contributed most for an individual participant. The reported group percentages also do not predict how a particular person will respond. No medical advice or individual treatment decision follows from these group summaries.

The result is limited to the stated population, endpoint, and week 16 assessment. It does not alone establish longer-term outcomes, results in participants outside the primary subgroup, or effects on every secondary measure. Although the study’s official title describes long-term evaluation, the primary comparison concerns week 16. The registry record does not report all details of missing-data handling, multiplicity control, or the full statistical analysis plan.

The sponsor’s reported odds ratio and the unadjusted recalculated risk difference use different statistical scales and methods. Their values should not be treated as competing estimates of the same quantity. The sponsor’s analysis is the trial’s reported model-based result; the recalculation provides a straightforward description based on the posted response summaries. Both should be interpreted with their respective uncertainty and assumptions in mind.

The safety summary is also descriptive. The event counts are reported for distinct treatment and follow-up groupings, and the record does not provide sufficient information to equate their exposure periods or infer causality. Taken together, the registry data permit a focused description of the week 16 response contrast and listed safety counts, but do not answer every question about long-term outcomes, mechanisms, or individual benefit and risk.

18. Why This Trial Matters Statistically

This trial is statistically informative because it reports a randomized, double-blind, placebo-controlled comparison with a clearly defined primary response endpoint and a specific assessment time. Those features give the week 16 group contrast a clear target: the proportion achieving ASAS40 in biological disease-modifying antirheumatic drug-naïve participants with endpoint data.

The primary response is presented both as group percentages and through the sponsor’s logistic regression analysis. The simple unadjusted recalculation adds a risk-difference perspective, while the registry’s analysis uses an odds ratio. Seeing these measures as distinct estimands helps prevent a common interpretive error: reading a relative measure as if it were an absolute percentage-point difference. The confidence intervals also emphasize that estimates have uncertainty, even when the reported p-value is small.

The analysis population matters as much as the endpoint definition. The primary result is based on the stated subgroup, whereas another ASAS40 result includes different group sizes. Keeping these analyses separate avoids extending a subgroup result to a broader population without evidence. The presence of several secondary outcomes offers context across disease activity, function, imaging, and health-related quality of life, but the missing multiplicity details limit their confirmatory interpretation.

The registry record also illustrates why statistical interpretation depends on reporting completeness. The original sample-size rationale, missing-data procedures, detailed model specifications, and multiplicity strategy are not reported. Those omissions do not erase the posted estimates, but they constrain how fully readers can evaluate the analysis plan and uncertainty. Clear reporting of populations, estimands, analysis choices, and safety periods is central to judging what a clinical trial comparison can support.

19. 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.
• Participant counts were reconstructed from posted percentages and arm sizes, so small rounding differences are possible.

The primary endpoint population is a defined subgroup: biological disease-modifying antirheumatic drug-naïve participants with ASAS40 data. The registry record does not provide a full participant flow or explain how participants without endpoint data were handled. Consequently, the relationship between the primary analysis population and all randomized participants cannot be fully assessed from the posted summaries.

The record identifies logistic regression for the sponsor’s primary analysis but does not report the covariates or detailed model specifications. The original sample-size justification, interim-analysis plans, and missing-data methods are also not reported in the registry record. These missing details limit independent reconstruction of the prespecified statistical approach.

Many secondary outcomes are listed, but multiplicity control and the inferential status of the secondary analyses are not reported. The secondary results therefore provide context, but their interpretation as confirmatory findings is uncertain. In addition, the primary result is at week 16; the presence of an extension period in the study description does not supply long-term endpoint results in the primary analysis.

The safety counts are separated into treatment and follow-up groupings. Without further information about exposure duration, movement between groups, and event attribution, these counts should not be treated as directly comparable risks or as evidence that treatment caused a particular event. The registry record also does not provide all details needed to assess the generalizability of the findings beyond the studied Chinese participants and the specified primary subgroup.

20. Related Tutorials

21. Related Statistical Calculators

22. Sources

• ClinicalTrials.gov: A Study of Ixekizumab (LY2439821) in Chinese Participants With Radiographic Axial Spondyloarthritis — NCT04285229.
• Registry record last updated 2023-04-14; status last verified 2023-04.
• Results first posted 2022-06-28.
• 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.

23. Record Summary

NCT04285229 is a completed phase 3, randomized, double-blind, parallel-group, placebo-controlled study of ixekizumab in Chinese participants with radiographic axial spondyloarthritis. The primary endpoint was ASAS40 response at week 16 in biological disease-modifying antirheumatic drug-naïve participants with endpoint data.

The posted primary response percentages were 7.8% for placebo and 40.9% for ixekizumab 80mg Q4W. The registry reports a logistic regression odds ratio of 7.64, a 95% confidence interval from 2.68 to 21.76, and p <0.001. An unadjusted recalculation gives a risk difference of 0.331 and p <0.001; this is a different measure from the sponsor’s odds ratio.

The registry lists secondary efficacy outcomes and safety counts across separate treatment and follow-up periods. Details of the original sample-size rationale, missing-data handling, multiplicity strategy, and full statistical model specifications are not reported in the registry record.