Carotid Angioplasty and Stenting Versus Endarterectomy in Asymptomatic Subjects Who Are at Standard Risk for Carotid Endarterectomy With Significant Extracranial Carotid Stenotic Disease (ACT I): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Carotid Angioplasty and Stenting Versus Endarterectomy in Asymptomatic Subjects Who Are at Standard Risk for Carotid Endarterectomy With Significant Extracranial Carotid Stenotic Disease (ACT I) (NCT00106938), a randomized na study. The primary outcome is Composite of Death, Stroke (Ipsilateral or Contralateral; Major or Minor) and Myocardial Infarction (DSMI) Through 30 Days Post-procedure, Plus Ipsilateral Stroke 31 to 365 Days..

2. Clinical Question

3. Trial Design

ACT I was a randomized, parallel-group trial comparing carotid artery stenting with carotid endarterectomy. The record lists masking as none. It describes a 3:1 allocation ratio of CAS to CEA and reports enrollment of 1663 participants: 1089.0 in the CAS group and 364.0 in the CEA group. The sponsor was Abbott Medical Devices, and the phase is listed as NA.

The study was conducted in asymptomatic subjects with significant extracranial carotid stenotic disease who were at standard risk for carotid endarterectomy. The CAS intervention used the Emboshield Embolic Protection System with the Xact Carotid Stent System; the comparator was surgical endarterectomy. The trial description states that the study was intended to demonstrate non-inferiority. The non-inferiority margin, the assumptions used for the original design, and the original sample-size justification are not reported in the registry record.

The arm descriptions specify follow-up at 30 days, six months, and 12 months after the procedure, then annually for four additional years. The primary outcome covers 0 to 365 days, and the posted secondary outcomes include measures over specified periods within that span. The registry record lists the study status as terminated, with a start date of 2005-04 and primary completion of 2013-03. The reason for termination is not reported in the registry record, and the record does not establish whether the planned longer follow-up was completed.

The group sizes are unequal, consistent with the stated allocation ratio. General statistical context: unequal allocation can affect the precision of a comparison relative to equal allocation, but the reason for the chosen allocation and its expected impact on the original design are not reported in the registry record. No formal analysis entries are reported, although outcome percentages and comparison statistics are posted.

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.

Before assignment: 1453 patients were randomized to support the primary analysis; an additional 210 lead-in subjects were enrolled to allow investigators to gain experience with the study devices prior to randomizing subjects and were not part of the primary analysis.

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 Composite of Death, Stroke (Ipsilateral or Contralateral; Major or Minor) and Myocardial Infarction (DSMI) Through 30 Days Post-procedure, Plus Ipsilateral Stroke 31 to 365 Days., measured over 0 to 365 days.

The primary endpoint is the percentage of participants experiencing a composite event from the procedure through 365 days. It combines death, ipsilateral or contralateral stroke of either major or minor severity, and myocardial infarction through 30 days after the procedure with ipsilateral stroke from 31 to 365 days. The registry labels the measure as a number of participants and gives its unit as percentage of participants.

General statistical context: a composite endpoint combines multiple kinds of events into a single outcome. This can capture a broader range of clinically important events than a single component would, but the components may differ in frequency and clinical meaning. The combined result does not, by itself, show which component accounts for the observed event percentage. Component-specific results for this primary composite are not reported in the registry record.

The registry describes non-inferiority as the study objective. A non-inferiority conclusion requires interpreting the estimated difference against a prespecified margin, along with the planned analysis approach. The margin and the trial's original analysis plan are not reported in the registry record. Therefore, the composite is useful for describing the posted comparison, but the record does not provide enough information to determine whether the planned non-inferiority criterion was satisfied.

7. Results Posted in the Registry

• CEA Group: 3.3% (12/364) versus 3.8% (41/1089) on control; risk difference -0.5 percentage points (95% CI -2.6 to 1.7), risk ratio 0.88 (0.47–1.65); unadjusted two-proportion z-test p = 0.680.

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.

Freedom From Ipsilateral Stroke

• 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:
  • CEA Group: 99.1% (330/333) versus 99.4% (1043/1049) on control; risk difference -0.3 percentage points (95% CI -1.4 to 0.8), risk ratio 1.00 (0.99–1.01); unadjusted two-proportion z-test p = 0.516.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between CEA Group and the control. The interval gives the range of effects that remain compatible with the data.

Freedom From Mortality

• 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:
  • CEA Group: 99.2% (361/364) versus 98.5% (1073/1089) on control; risk difference 0.6 percentage points (95% CI -0.5 to 1.8), risk ratio 1.01 (0.99–1.02); unadjusted two-proportion z-test p = 0.348.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between CEA Group and the control. The interval gives the range of effects that remain compatible with the data.

Freedom From All Stroke

• 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:
  • CEA Group: 97.8% (356/364) versus 96.5% (1051/1089) on control; risk difference 1.3 percentage points (95% CI -0.6 to 3.2), risk ratio 1.01 (0.99–1.03); unadjusted two-proportion z-test p = 0.223.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between CEA Group and the control. The interval gives the range of effects that remain compatible with the data.

The secondary results cover freedom from ipsilateral stroke, mortality, and all stroke. In broad terms, the posted percentages are high, and the unadjusted comparison intervals include no difference. The secondary comparisons therefore do not present a clearly separated pattern of results across these outcomes. Their direction and precision vary, but none should be read as a standalone confirmation of the primary finding.

These outcomes relate to the primary composite because stroke and death are components or closely related outcomes, while the primary measure also includes myocardial infarction and has a specific time structure. Secondary endpoints can help describe individual outcome domains that are combined in a composite. They do not, however, supply the component breakdown for the primary endpoint unless the corresponding definitions and results directly match; that breakdown is not reported in the registry record.

The registry reports no formal analysis entries for the secondary outcomes. Their comparisons are unadjusted, and the record does not report a plan for controlling the chance of misleading findings when many outcomes are assessed. General statistical context: examining multiple outcomes creates more opportunities for a result to appear noteworthy by chance. Without a prespecified hierarchy or multiplicity adjustment, secondary p-values and intervals should be interpreted cautiously and are less persuasive as confirmatory evidence.

The secondary findings can be used as descriptive context for the primary result, but they do not resolve the missing non-inferiority margin or analysis details. They also do not establish that outcomes not posted were absent or unchanged. The registry lists 32 posted secondary outcomes, while the detail available for interpretation depends on the results and comparison information recorded for each measure.

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

• Acute Device Success: Xact Carotid Stent
• Acute Device Success: Embolic Protection Device System
• Procedural Success
• Composite Morbidity Measure
• Freedom From Clinically Indicated Target Lesion Revascularization(CI-TLR)
• Freedom From Clinically Indicated Target Lesion Revascularization
• Freedom From Clinically Indicated Target Lesion Revascularization
• Freedom From Clinically Indicated Target Lesion Revascularization

9. Statistical Interpretation

10. Statistical Methods Explained

The registry reports percentages of participants with events for the primary and secondary outcomes. For the primary endpoint, the groups are presented as CAS and CEA, with the comparison given as a risk difference. The group percentages are 3.8% and 3.4%, respectively. The registry's risk-difference estimate is -0.005 for CEA relative to CAS. The estimate's sign depends on the comparison order; it should not be read as a separate event percentage.

What does a risk difference describe?

General statistical explanation: a risk difference subtracts one group's event proportion from the other group's event proportion. A value of zero corresponds to equal proportions. Positive and negative values indicate direction according to the stated comparison order. Unlike a relative measure, a risk difference is on the absolute probability scale. It describes the difference in observed proportions, not a causal mechanism or a guarantee about an individual participant.

What does a confidence interval add?

General statistical explanation: a confidence interval describes uncertainty around an estimated effect under the statistical method used. Wider intervals indicate less precision than narrower intervals on the same scale. An interval that includes zero does not identify a clear difference under the conventional null comparison, but it does not prove that the groups are identical. For the primary endpoint, the reported 95% interval is -0.026 to 0.017. The interval includes zero and values on both sides of it. Its interpretation is constrained by the analysis details that are not reported in the registry record.

How should the p-value be read?

General statistical explanation: a p-value measures how unusual results at least as incompatible with a specified null model would be, assuming that model and the calculation's conditions. It is not the probability that the null hypothesis is true, and it does not measure the size or clinical importance of an effect. The primary unadjusted p-value is 0.68. It should be read alongside the effect estimate and its interval, not in isolation. The registry does not report a multiplicity adjustment or a prespecified testing hierarchy for the posted outcomes.

Why does the non-inferiority objective need additional information?

General statistical explanation: non-inferiority asks whether the results rule out an unacceptable loss relative to a comparator, using a margin set before interpreting the trial outcome. The estimate and confidence interval must be judged against that margin and the planned analysis. The record says that demonstrating non-inferiority was the study objective, but the margin, analysis population, and formal analysis approach are not reported in the registry record. The posted unadjusted comparison therefore cannot be treated as a complete non-inferiority assessment.

The registry lists 33 outcome measures and 32 posted secondary outcomes, but reports zero analysis entries. That distinction matters: a posted percentage and an unadjusted comparison are statistical results, but they do not supply the full analysis protocol or its implementation. The handling of missing observations, the analysis population, covariate adjustment, and any interim analyses are not reported in the registry record.

General statistical explanation: binary outcomes are proportions, and their precision depends in part on the number of participants contributing data and the frequency of events. A comparison with few events can have appreciable uncertainty even when the group percentages look similar. For the primary result, the registry provides group sizes and an interval, which gives more information about precision than the point estimate alone. The record does not describe any additional modeling or adjustment behind the posted comparison.

Since no discrepancy is flagged for the primary comparison, the reported registry estimate and interval are used as posted. They should not be confused with the separate planning illustrations: those are calculations based on observed effects under stated assumptions, not the trial's original design justification or a measure of the trial's achieved power.

11. Confidence Intervals and Precision

The primary risk-difference estimate is -0.005, with a 95% confidence interval from -0.026 to 0.017. The interval includes zero, so the posted data do not sharply distinguish a difference in either direction from no difference under this comparison. Its range also makes clear that the point estimate is not the only plausible value consistent with the calculation.

General statistical explanation: confidence intervals express uncertainty about an estimated effect, conditional on the data and statistical method. They do not assign a probability to the true effect, and a 95% interval is not a guarantee that the true value lies within its particular limits. Precision is about the range of effects compatible with the data, not about whether an effect is clinically acceptable.

For a non-inferiority question, interval interpretation depends on the prespecified non-inferiority margin. That margin is not reported in the registry record. Consequently, the interval cannot be assessed against the trial's intended threshold using the registry record alone. The posted p-value does not substitute for that comparison, and the point estimate should not be mistaken for a demonstration of equivalence or non-inferiority.

The posted secondary intervals also convey uncertainty, but their unadjusted status and the absence of a reported multiplicity approach affect how much weight to place on them. The record does not report confidence intervals for every outcome measure. Further detail on analysis populations and missing observations is also not reported in the registry record, limiting the assessment of how precisely the results represent all randomized participants.

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.

The sample-size figures are planning illustrations per arm, not total event counts. The stated calculation assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The assumed effect to detect is a stated fraction of the observed effect. For this binary outcome, the displayed figures are participants per arm; the time-to-event convention for total events does not apply to these figures.

The 80% power column gives the planning number of participants per arm under which the calculation would have an 80% chance of detecting the specified effect, if the stated assumptions held. The 90% column gives the corresponding planning number for a 90% chance. These percentages refer to the operating characteristics of the hypothetical design, not to the probability that a result is true or that a particular treatment is better.

The rows describe planning for 100%, 75%, and 50% of the observed effect. A smaller target effect generally requires more participants to distinguish it from no difference at the same significance level and power target. The figures are therefore sensitive to the assumed effect size; the observed effect is not necessarily the effect a future study should target.

These illustrations are not observed power. They are not the trial's original sample-size justification, and they do not show that the trial was adequately sized for its planned non-inferiority objective. The original design assumptions, including any non-inferiority margin, are not reported in the registry record. The equal-allocation assumption in the illustration also differs from the trial's stated 3:1 allocation.

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 = 0.038; treatment proportion p₁ = 0.033; average p̄ = 0.035.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.2610 = 0.5116.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.2610 = 0.2196.
4. n = (0.5116 + 0.2196)² / (-0.0047)² = 24,388.4, rounded up to 24,389 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 <- 0.0376492194674013                          # control proportion
p1 <- 0.032967032967033                          # 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(106938)
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 = 24,389 (80% power), 32,649 (90% power)
 75% of observed effect: n per arm = 44,050 (80% power), 58,970 (90% power)
 50% of observed effect: n per arm = 100,669 (80% power), 134,767 (90% power)
power.prop.test: 24388.4 
Simulated power at n = 24,389 per arm: 0.798 (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. Multiplicity, Missing Data and Analysis Populations

The registry lists 33 outcome measures and 32 posted secondary outcomes, while the reported analysis-entry count is zero. This does not mean there are no numerical results: percentages and unadjusted comparisons are posted. It does mean that a formal account of the analyses is not reported in the registry record. The analysis plan, prespecified outcome hierarchy, and approach to multiple comparisons are not reported.

Multiplicity matters because a trial may assess many outcomes, time periods, or comparisons. General statistical explanation: when many hypotheses are tested, the chance of at least one apparently unusual result can rise unless the analysis accounts for the testing structure. The record does not report whether or how multiplicity was addressed, so individual secondary comparisons should be treated as descriptive rather than as definitive confirmatory tests.

The handling of missing outcome data and the definition of the analysis population are not reported in the registry record. The primary group sizes are 1089.0 and 364.0, while some secondary outcomes have different group denominators. The registry does not explain those differences, so they should not be attributed to a particular pattern of missingness, exclusion, or follow-up without additional information. The record also does not report whether the primary analysis followed an intention-to-treat, per-protocol, or other population definition.

The original sample-size assumptions and the non-inferiority margin are not reported in the registry record. Interim analyses, stopping rules, covariate adjustment, and the statistical methods used for any formal sponsor analysis are also not reported. These omissions limit reconstruction of the intended inferential framework and make it difficult to judge whether the posted comparison corresponds to the trial's planned primary analysis.

The terminated status is recorded, but the reason for termination is not reported in the registry record. The status alone does not establish that the trial stopped early for a particular reason, nor does it describe the consequences for follow-up or analysis. Those questions require information not contained in the registry entry.

15. 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: hypotension (6.3%), coronary artery disease (5.8%), peripheral vascular disease (3.8%), musculoskeletal (3.8%), gastrointestinal (2.7%).

The registry reports serious adverse events affecting 376 of 1089 participants in the CAS group and 118 of 364 participants in the CEA group. Other adverse events are reported for 635 of 1089 participants in the CAS group and 216 of 364 participants in the CEA group. These are counts of participants with events against the listed groups at risk; they are not descriptions of event severity beyond the registry's serious-versus-other categories.

The record lists serious-event terms and percentages, including hypotension at 6.3%, coronary artery disease at 5.8%, peripheral vascular disease at 3.8%, musculoskeletal events at 3.8%, gastrointestinal events at 2.7%, and target lesion restenosis at 2.5%. The registry does not provide a group-specific comparison for these terms in the information recorded here, so the percentages should not be interpreted as comparative treatment effects.

Deaths are listed as null in the adverse-event fields, so death counts from that safety record are not reported in the registry record. Adverse-event counts alone do not establish causation, and the record does not provide enough detail to assess event timing, severity within categories, or adjusted differences between groups.

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

The posted primary result describes a comparison of the one-year composite endpoint in randomized groups. The event percentages are 3.8% for CAS and 3.4% for CEA, with a reported risk difference of -0.005 and a 95% confidence interval from -0.026 to 0.017. The unadjusted p-value is 0.68. The interval includes zero and spans estimates in both directions, so the point estimate alone should not be treated as a conclusive difference between groups.

The result does not establish equivalence. A lack of a clear difference under an unadjusted comparison is not proof that the procedures have identical outcomes. It also does not, on its own, demonstrate non-inferiority. Although the registry states that non-inferiority was the study objective, the non-inferiority margin and formal analysis plan are not reported in the registry record. Without those details, the intended criterion cannot be evaluated from the posted point estimate and interval alone.

The composite outcome does not identify the contribution of its separate components. The registry result combines death, stroke, and myocardial infarction through 30 days with ipsilateral stroke from 31 to 365 days. Component-specific primary results are not reported in the registry record. The secondary outcomes offer additional descriptive measures but are unadjusted, and no multiplicity plan is reported.

These registry results should also be considered alongside the missing information about analysis populations, missing data, original design assumptions, and the reason for the terminated status. The findings describe what is posted; they do not support medical advice or a recommendation about which procedure to choose. They also do not establish outcomes beyond the reported periods or explain whether planned longer-term follow-up was completed.

17. Why This Trial Matters Statistically

Statistically, ACT I is notable for posing a non-inferiority question rather than simply asking whether two groups differ. That distinction changes how results must be interpreted: a non-inferiority conclusion depends on a prespecified margin and analysis plan. The registry states the objective but does not report the margin or the formal plan, making the posted unadjusted estimate informative as a comparison but insufficient to reconstruct the intended non-inferiority test.

The trial used randomized parallel groups with a 3:1 allocation ratio and no masking. The larger CAS group and smaller CEA group are relevant to understanding the precision of the comparison. General statistical context: allocation proportions affect how information is distributed between groups, while the estimated effect and its interval show the uncertainty actually reported. The reason for the ratio is not reported in the registry record.

The primary endpoint is a composite with a defined time structure, and its interval includes zero while extending in both directions. This makes the distinction between a point estimate and its uncertainty especially important. A reader should not equate a non-significant unadjusted comparison with proof of equal outcomes, nor treat the point estimate as a non-inferiority result without the margin.

The record also illustrates the value of separating posted outcome figures from the details of a trial's statistical plan. Results are available, but analysis entries, missing-data methods, population definitions, multiplicity handling, and the reason for termination are not reported. These limits are central to evaluating the strength and scope of the statistical conclusions.

18. 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.

Several limitations are specific to interpreting this registry record. The study focused on asymptomatic subjects with significant extracranial carotid stenotic disease who were at standard risk for endarterectomy. The results therefore describe that recorded trial population and should not be assumed to characterize other populations or clinical settings.

The trial is listed as terminated, but the reason is not reported in the registry record. The arm descriptions specify follow-up through annual visits for four additional years after the earlier scheduled visits; the record does not establish whether that planned follow-up was completed. The primary endpoint itself covers 0 to 365 days, so it does not by itself describe longer-term outcomes.

The registry's stated objective was non-inferiority, but the margin and original design assumptions are not reported. The record also does not report the original sample-size justification, formal analysis methods, analysis population, handling of missing data, multiplicity approach, or interim analyses. Those omissions prevent a full assessment of whether the posted unadjusted result corresponds to the intended confirmatory analysis.

The primary outcome is composite, and component-specific results are not reported in the registry record. Secondary results are unadjusted, with no reported multiplicity plan. Adverse-event information is presented as group counts and listed serious-event terms, but the record does not provide a detailed comparative safety analysis or explain the null death fields. These gaps limit the conclusions that can be drawn from the posted results without additional trial reporting.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Carotid Angioplasty and Stenting Versus Endarterectomy in Asymptomatic Subjects Who Are at Standard Risk for Carotid Endarterectomy With Significant Extracranial Carotid Stenotic Disease (ACT I) — NCT00106938.
• Registry record last updated 2017-07-19; status last verified 2017-06.
• Results first posted 2014-10-21.
• 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.

22. Record Summary

ACT I (NCT00106938) compared carotid artery stenting with carotid endarterectomy in asymptomatic subjects at standard risk for endarterectomy. The record lists randomized allocation, a parallel model, no masking, and enrollment of 1663 participants. The sponsor is Abbott Medical Devices, and the phase is listed as NA.

The study start is recorded as 2005-04, with primary completion in 2013-03 and status listed as terminated. The primary outcome is a composite through 365 days. The posted percentages are 3.8% for CAS and 3.4% for CEA, with a risk-difference estimate of -0.005 and a 95% confidence interval from -0.026 to 0.017. The registry describes non-inferiority as the study objective; the margin and formal analysis plan are not reported in the registry record.