The ACTIVE (Use of the Assurant® Cobalt Iliac Stent System in the Treatment of Iliac Vessel Disease) Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The ACTIVE (Use of the Assurant® Cobalt Iliac Stent System in the Treatment of Iliac Vessel Disease) Study (NCT00753337), a na na study. The primary outcome is Major Adverse Events (MAE), Measured as Device and/or Procedure Related Death, Target Limb Loss and/or Clinically Driven Target Lesion Revascularization (TLR) or Target Vessel Revascularization (TVR)..

2. Clinical Question

The study objective was to evaluate safety and efficacy of the stent system for de novo and restenotic iliac artery lesions in people with peripheral artery disease. Its primary endpoint focuses on major adverse events over 9 months. That endpoint combines serious clinical events and repeat revascularization into a single measure; the registry record does not report the observed percentage or an event count for it.

Because the record describes a single group rather than a randomized comparison, the clinical question is descriptive: what outcomes were recorded among participants treated with the device? It does not provide a concurrent control group for estimating how outcomes would differ under another treatment or strategy. The registry record also does not report a primary endpoint analysis or an estimate of the treatment effect.

3. Trial Design

The ACTIVE study is registered as a completed, single-group device study of the Assurant Cobalt Iliac Stent System. The listed condition is peripheral vascular disease, and the study objective concerns treatment of de novo and restenotic lesions in iliac arteries among people with peripheral artery disease. Enrollment is 123. The registry record lists the study start as 2008-10 and primary completion as 2011-02.

There is one listed intervention and one arm description, both naming the Assurant Cobalt Iliac Stent System. Allocation is listed as NA, and the study model is single group. Masking is listed as none. These features mean the record does not describe random assignment, blinding, or a parallel control arm. A like-for-like treatment comparison therefore cannot be made from the design information presented.

Phase is listed as NA. A sample-size justification, detailed protocol, and statistical analysis plan are not reported in the registry record. The record lists 11 outcome measures and 0 analyses. Although the study is marked completed, completion status alone does not establish that the primary endpoint result is available in the registry. In this record, that result is not reported.

The listed secondary outcomes include primary patency at 9 months, device success, lesion success, procedure success, clinical success, and hemodynamic success. Clinical success and hemodynamic success each appear more than once in the list. Their detailed definitions and analysis results 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

Analysis population for the primary outcome, as defined in the registry: Intent to Treat population (ITT)

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 Major Adverse Events (MAE), Measured as Device and/or Procedure Related Death, Target Limb Loss and/or Clinically Driven Target Lesion Revascularization (TLR) or Target Vessel Revascularization (TVR)., measured over 9 months.

The primary endpoint is the percentage of participants with major adverse events by 9 months. The event definition includes device and/or procedure related death, target limb loss, and clinically driven target lesion revascularization or target vessel revascularization. This is a composite endpoint: different types of events contribute to the same overall measure.

Composite endpoints can capture a range of clinically important outcomes in a single summary. Their interpretation depends on knowing the component events, how they were counted, and whether one component contributes much more often than the others. The registry record does not report component counts or the overall endpoint percentage, so the relative contribution of each event type cannot be assessed.

The primary population is described as the Intent to Treat population, but the percentage is based on participants evaluable for major adverse events. A participant is considered unevaluable by 9 months under specified circumstances: withdrawal before 240 days without a major adverse event; loss to follow-up before 240 days without an event and with no later contact; or a device- and/or procedure-unrelated death before 240 days without an event. This rule affects the denominator used for the reported percentage. The registry record does not report the number evaluable or the endpoint result.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is a binary participant-level measure: a participant either meets the major adverse event definition within the specified period or does not. The registry describes the result in percentage terms. In general, such a percentage is interpreted together with its numerator, the number of participants meeting the definition, and its denominator, the number whose outcome could be evaluated. Neither the primary endpoint numerator nor its denominator is reported in the registry record, so no endpoint percentage can be interpreted from this record.

What does the endpoint denominator mean?

The population is identified as Intent to Treat, a general analysis principle that retains participants in the group to which they were assigned, regardless of later treatment changes. In this study, the record describes one group and no allocation to different groups. It also states that the primary endpoint percentage is based on participants evaluable for major adverse events. The record defines situations that make a participant unevaluable by 9 months: certain withdrawals or losses to follow-up before 240 days without a recorded event, and a device- and/or procedure-unrelated death before 240 days without an event. This means the denominator for the endpoint is governed by the stated evaluability rule, but its actual size is not reported.

How should a percentage be read?

As a general statistical point, an event percentage is a descriptive summary of the observed participants who meet a definition within a follow-up period. It is not by itself evidence of a difference from another treatment, especially when there is no comparator group. Its interpretation depends on the event definition, follow-up completeness, and denominator. Here, the composite definition includes several kinds of event, but no event count, percentage, or component breakdown is reported for the primary endpoint.

A confidence interval is a general way to express uncertainty around an estimate. A narrower interval indicates greater precision under the method used; a wider interval indicates less precision. It does not guarantee that the estimate equals the underlying event frequency, and it does not resolve limitations in study design or missing follow-up. No confidence interval or method for calculating one is reported for the primary endpoint.

What can the design establish?

The record identifies a single-group model, allocation as NA, and masking as none. General methods interpretation follows from those design features: the study can describe outcomes observed in the treated group, but without a concurrent comparator it cannot directly quantify a difference between treatment strategies. The registry record does not report an analysis that adjusts for other factors or estimates a comparative effect. A statistical plan, including the planned analysis method, is not reported.

The study lists 11 outcome measures, including the primary endpoint and several secondary outcomes. When many outcomes are examined, the chance of finding an apparently notable result by chance can increase. As a general statistical approach, multiplicity procedures can address that issue, but the record does not report whether any such procedure was planned or used. It also does not report results for the listed secondary outcomes.

How do the planning assumptions relate to the trial?

The registry record describes planning illustrations using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It says that the effect to detect is a stated fraction of the observed effect. These are hypothetical calculation assumptions, not a description of the enrolled study: the trial itself is listed as single group and has no separate comparator arm. The illustrations are not observed power and do not establish the study’s original design justification. The specific sample-size values and effect fractions are not reported in the registry record.

The record also describes a Schoenfeld approach for total event counts in time-to-event illustrations, while other illustrations use participants per arm. These are general planning conventions, not observed trial outcomes. The primary endpoint is reported as a percentage of participants with an event by 9 months; the record does not provide a time-to-event analysis or a primary endpoint analysis. The study’s own sample-size rationale and statistical plan are not reported.

Over-dispersion is a general concern when observed variability exceeds what a statistical model assumes. It is often relevant to count or clustered data, but the registry record does not identify such a model for this endpoint. There is no basis in the record to say that over-dispersion was assessed or that a particular model was used. The central limitation for interpreting the primary endpoint is more direct: its estimate, denominator, and uncertainty are not reported.

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("Assurant Cobalt Iliac Stent")
n      <- c(123)
events <- c(1)
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  Assurant Cobalt Iliac Stent  123  1  0.8  0.0  4.4  0.1  4.5  0.2  4.4

11. Multiplicity, Missing Data and Analysis Populations

The record lists 11 outcome measures, including a primary endpoint and secondary outcomes such as primary patency at 9 months, device success, lesion success, procedure success, clinical success, and hemodynamic success. Clinical success and hemodynamic success appear repeatedly in the listed outcomes. The record does not explain the repeated entries, provide their detailed definitions, or report results for the secondary outcomes.

When a study evaluates multiple endpoints, multiplicity is a general statistical concern: repeated testing can increase the chance of at least one apparently positive result arising by chance. A prespecified testing hierarchy or adjustment can help manage that concern. Whether the ACTIVE study used an adjustment, a hierarchy, or another multiplicity strategy is not reported in the registry record. No interim analyses or statistical analysis plan are reported either.

The record lists 0 analyses. It does not provide a primary endpoint numerator, evaluable denominator, percentage, confidence interval, or test result. Therefore, there is no reported analysis from which to assess missing-data handling beyond the endpoint’s stated evaluability criteria.

For the primary outcome, the registry defines participants as unevaluable in specified circumstances involving withdrawal, loss to follow-up, or a device- and/or procedure-unrelated death before 240 days without a major adverse event. The record does not report how many participants met those conditions, how many were evaluable, or whether other missing observations occurred. The treatment of missing values for secondary outcomes is not reported in the registry record. The stated Intent to Treat population and the evaluable-subject denominator should therefore be read as distinct descriptions: the former identifies the population, while the latter defines the basis for the primary percentage.

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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: vascular disorders (12.2%), cardiac disorders (11.4%), infections and infestations (6.5%), injury, poisoning and procedural complications (4.1%), musculoskeletal and connective tissue disorders (4.1%).

For the Assurant Cobalt Iliac Stent group, the registry records 37 participants affected by serious adverse events among 123 at risk, and 78 affected by other adverse events among 123 at risk. These are adverse-event reporting figures, not the primary major adverse event endpoint result. The endpoint has its own defined events and evaluability rules, and its result is not reported in the registry record.

The listed serious adverse-event categories are vascular disorders (12.2%), cardiac disorders (11.4%), infections and infestations (6.5%), injury, poisoning and procedural complications (4.1%), musculoskeletal and connective tissue disorders (4.1%), and general disorders and administration site conditions (2.4%). These are category percentages as listed in the registry. The record does not give event counts for each category or explain the category-specific denominators.

As a general point, participants can experience events from more than one category, so category percentages should not automatically be added to estimate an overall proportion. The record does not state whether participants contributed to multiple categories. Deaths are not reported in the adverse-event record. These safety summaries describe recorded events in the study group; without a comparator, they do not quantify a difference in risk between treatment strategies.

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

The record shows that the ACTIVE study evaluated the Assurant Cobalt Iliac Stent System in a single group of 123 participants. Its stated primary question concerned the percentage with major adverse events by 9 months, including device- and/or procedure-related death, target limb loss, and clinically driven target lesion or target vessel revascularization. The record also lists other outcomes and adverse-event summaries.

It does not report the primary endpoint event count, percentage, evaluable denominator, confidence interval, or analysis. As a result, the posted registry information does not allow readers to quantify the observed primary endpoint frequency or judge its statistical precision. Nor does it show which components, if any, contributed most to the composite endpoint.

The study’s single-group design matters to interpretation. Outcomes recorded among participants in that group cannot by themselves establish how outcomes would compare with a different device, procedure, or management strategy. The record does not describe a concurrent comparator, randomization, or masking. It therefore does not provide a direct estimate of a comparative treatment effect.

The adverse-event summaries add descriptive safety information: the record reports 37 participants affected by serious adverse events and 78 by other adverse events, each among 123 at risk. The serious-event category percentages provide additional classification, but do not replace the primary endpoint result or explain the relationship between broad adverse-event categories and the endpoint’s specific definition.

These limitations do not establish that the device was effective or ineffective, or that it was safe or unsafe. They identify what can and cannot be concluded from the registry record: the study objective, design, endpoint definition, enrollment, and some adverse-event summaries are available, while the primary outcome result and its uncertainty are not reported.

14. Why This Trial Matters Statistically

This study illustrates why the endpoint definition and the reporting of its denominator matter. The primary outcome is a composite of device- and/or procedure-related death, target limb loss, and clinically driven revascularization. Each component can have a different clinical meaning and frequency. An overall percentage, even if reported, would be more informative when accompanied by component counts and a clear explanation of who was included in the denominator. Those primary outcome details are not reported in the registry record.

The stated evaluability rule makes follow-up status especially relevant. Participants with specified withdrawals, losses to follow-up, or unrelated deaths before 240 days can be excluded from the endpoint denominator if they had no major adverse event. Reporting the number evaluable and the reasons for non-evaluability would help readers understand how much of the enrolled group contributes to the endpoint estimate. Neither is reported.

The design also demonstrates the distinction between a descriptive study and a comparative trial. A single-group study can document outcomes in the group studied, but it does not provide a concurrent reference group for estimating a treatment difference. A planning illustration that assumes equal allocation between two arms does not change the registered study’s single-group design or create comparative evidence.

Finally, a completed study record and an outcome definition do not substitute for a reported analysis. Without the primary endpoint estimate and its uncertainty, readers cannot assess the observed frequency or its precision. Clear outcome reporting is essential for statistical interpretation, particularly when multiple endpoints and missing follow-up may affect what the results mean.

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 most important limitation for interpretation is that the primary endpoint result is not reported in the registry record. The endpoint count, percentage, evaluable denominator, confidence interval, and statistical test are absent. The record lists 0 analyses, so no posted primary analysis can be assessed.

The single-group design has no described comparator arm, and allocation is listed as NA. Masking is listed as none. These design features limit what can be inferred about comparative effects and can leave outcome assessment open to influences that blinding might otherwise reduce. The registry record does not report whether any other safeguards or adjustment methods were used.

The primary endpoint’s evaluability rules are specified, but the number of participants classified as unevaluable and the number included in the endpoint denominator are not reported. The record also does not provide a breakdown of the composite endpoint into its component events. Without those details, neither missing follow-up nor the contribution of different event types can be assessed.

The record lists multiple outcomes but does not report the results, detailed definitions, or a multiplicity strategy. It also does not report an interim-analysis plan, statistical analysis plan, or sample-size justification. The planning assumptions described for hypothetical calculations do not establish the original study’s design rationale, particularly because those calculations assume two-arm allocation while the trial is listed as single group.

Adverse-event summaries are available, but the record does not give category-specific event counts or explain whether participants can appear in more than one category. Deaths are not reported in the adverse-event record. These reporting gaps constrain interpretation of the safety summaries and do not resolve the missing primary endpoint result.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: The ACTIVE (Use of the Assurant® Cobalt Iliac Stent System in the Treatment of Iliac Vessel Disease) Study — NCT00753337.
• Registry record last updated 2016-04-04; status last verified 2016-02.
• Results first posted 2013-12-30.
• 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 ACTIVE study is a completed, single-group device study of the Assurant Cobalt Iliac Stent System for de novo and restenotic iliac artery lesions in people with peripheral artery disease. Enrollment is 123. The registry lists no allocation and no masking. The primary endpoint is the percentage of participants with major adverse events by 9 months, based on participants evaluable under the stated follow-up rules.

The registry record does not report the primary endpoint result, its denominator, a confidence interval, or a statistical analysis. It lists 11 outcome measures and 0 analyses. Adverse-event reporting records 37 participants affected by serious events and 78 by other events among 123 at risk; deaths are not reported. The single-group design does not provide a concurrent comparison, and the record does not report a statistical analysis plan, multiplicity approach, or sample-size justification.