This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record.
1. Trial at a Glance
WARCEF was a completed phase 3 randomized, double-masked, parallel-group trial comparing warfarin with aspirin in a cardiovascular prevention setting. The primary endpoint was the event rate per 100 patient-years for a composite of ischemic stroke, intracerebral hemorrhage, or death, followed from randomization for up to 6 years.
| Feature | WARCEF |
|---|---|
| Trial name | Warfarin Versus Aspirin in Reduced Cardiac Ejection Fraction (WARCEF) Trial |
| Phase | Phase 3 |
| Therapeutic area | Cardiovascular |
| Conditions | Heart Disease; Stroke; Ischemic Heart Disease; Myocardial Infarction |
| Design | Randomized, double-masked, parallel-group |
| Allocation | Randomized |
| Primary purpose | Prevention |
| Enrollment | 2,305 |
| Start | October 2002 |
| Primary completion | August 2011 |
| Lead sponsor | Columbia University |
| Primary endpoint type | Count / rate |
| Primary analysis | Cox proportional-hazards model |
| Additional rate analysis | Poisson regression |
2. Clinical Question
The central statistical question was whether time to the first event in the composite of ischemic stroke, intracerebral hemorrhage, or death differed between patients randomized to warfarin and those randomized to aspirin.
Population
The trial enrolled 2,305 patients in a cardiovascular prevention trial involving reduced cardiac ejection fraction.
Intervention
Warfarin.
Comparator
Aspirin.
Primary question
Does time to first ischemic stroke, intracerebral hemorrhage, or death differ between warfarin and aspirin?
3. Trial Design
Aspirin
- Randomized aspirin group
- Comparator for the primary and secondary time-to-event analyses
- Denominator for the reported hazard ratios and rate ratios
Warfarin
- Randomized warfarin group
- Numerator for the reported hazard ratios and rate ratios
- Compared with aspirin under an intention-to-treat framework
The registry describes the allocation as randomized, the design model as parallel, and masking as double. The statistical analyses were based on the randomized treatment groups rather than an exposure-defined comparison.
4. Endpoints
Primary Endpoint
| Endpoint | Registry definition | Analysis |
|---|---|---|
| Event Rate Per 100 Patient Years for Composite Endpoint of Ischemic Stroke, Intracerebral Hemorrhage, or Death | The time, in years, from randomization to the first to occur of ischemic stroke, intracerebral hemorrhage, or death, up to a maximum of 6 years. Event rate per 100 patient years = 100 × (number of subjects with event) / patient-years of follow-up. Patient years of follow-up = sum(date of conclusion of follow-up − date of randomization + 1) of all randomized patients / 365.25. | Cox proportional-hazards model; hazard ratio |
Secondary Endpoint
| Endpoint | Time frame | Analysis |
|---|---|---|
| Event Rate Per 100 Patient-years for Composite Endpoint of Hospitalization for Heart Failure, Myocardial Infarction, Ischemic Stroke, Intracerebral Hemorrhage, or Death | From randomization to the first to occur of hospitalization for heart failure, myocardial infarction, ischemic stroke, intracerebral hemorrhage, or death, up to a maximum of 6 years. | Cox proportional-hazards model; hazard ratio |
Other Prespecified Endpoints
| Endpoint | Time frame | Analysis |
|---|---|---|
| Ischemic stroke | From date of randomization to date of ischemic stroke component of primary composite outcome, up to 6 years | Cause-specific Cox model |
| Intracerebral hemorrhage | From date of randomization to date of intracerebral hemorrhage component of primary composite outcome, up to 6 years | Cause-specific Cox model |
| Death | From date of randomization to date of death component of primary composite outcome, up to 6 years | Cause-specific Cox model |
| Myocardial infarction component | From date of randomization to date of myocardial infarction component of secondary composite outcome, up to 6 years | Cause-specific Cox model |
| Heart failure hospitalization component | From date of randomization to date of heart failure hospitalization component of secondary composite outcome, up to 6 years | Cause-specific Cox model |
| Ischemic stroke component of secondary composite | From date of randomization to date of ischemic stroke component of secondary composite outcome, up to 6 years | Cause-specific Cox model |
| Intracerebral hemorrhage component of secondary composite | From date of randomization to date of intracerebral hemorrhage component of secondary composite outcome, up to 6 years | Cause-specific Cox model |
| Death component of secondary composite | From date of randomization to date of death component of secondary composite outcome, up to 6 years | Cause-specific Cox model |
| Major hemorrhage | From date of randomization until end of scheduled follow-up, up to 6 years | Poisson regression; rate ratio |
| Minor hemorrhage | From date of randomization until the end of scheduled follow-up, up to 6 years | Poisson regression; rate ratio |
5. Statistical Methodology
Intention-to-treat analysis
The primary analysis population was an intention-to-treat population: all enrolled patients were analyzed. The same framework was specified for the secondary and other prespecified time-to-event analyses and for the hemorrhage rate analyses.
Cox proportional-hazards models
The primary endpoint was analyzed with a Cox proportional-hazards model. The same model family was used for the secondary composite and the individual component endpoints. For the individual components, the registry describes cause-specific Cox models that account for competing events through the modeling framework.
For the reported analyses, warfarin is the numerator and aspirin is the denominator. An HR below 1 therefore corresponds to a lower estimated instantaneous event hazard in the warfarin group, while an HR above 1 corresponds to a higher estimated instantaneous event hazard.
Stratification and covariate adjustment
The primary Cox models were stratified by site, New York Heart Association class (I vs. II-IV), and status with respect to recent stroke or transient ischemic attack. The primary analysis notes also describe adjustment for use of beta-blockers in the original sample-size assumptions. The individual component analyses were similarly stratified by site, NYHA class, and prior stroke or TIA status.
Poisson regression
Major and minor hemorrhage were analyzed as rates per 100 patient-years using Poisson regression. The corresponding effect measure was a rate ratio, with the warfarin group as numerator and aspirin as denominator.
Unlike a hazard ratio, which compares instantaneous event hazards in a time-to-event model, a rate ratio compares event rates expressed over accumulated patient-time. The distinction is important when interpreting recurrent or rate-based safety outcomes.
Superiority testing
The registry identifies the hypothesis type as superiority. For the primary endpoint, the null hypothesis was that time to first event in the composite endpoint did not differ significantly between warfarin and aspirin. The reported primary confidence interval was two-sided at the 95% level, and the corresponding P-value was 0.40.
6. Primary Result: Composite of Ischemic Stroke, Intracerebral Hemorrhage, or Death
The primary endpoint compared time from randomization to the first occurrence of ischemic stroke, intracerebral hemorrhage, or death, with follow-up extending up to 6 years.
Primary hazard ratio
95% CI: 0.79–1.10 · P = 0.40
Warfarin vs aspirin; intention-to-treat analysis; Cox proportional-hazards model
| Primary endpoint statistic | Reported value |
|---|---|
| Effect measure | Hazard ratio |
| Comparison | Warfarin vs aspirin |
| Estimate | 0.93 |
| 95% confidence interval | 0.79–1.10 |
| P-value | 0.40 |
| Analysis population | Intent-to-treat: all enrolled patients were analyzed |
| Model | Cox proportional-hazards model |
| Stratification | Site; NYHA class (I vs. II-IV); recent stroke or TIA status |
The estimated hazard ratio of 0.93 means that, under the fitted Cox model, the estimated instantaneous hazard of the first primary-composite event in the warfarin group was 0.93 times the corresponding hazard in the aspirin group. Expressed as a simple relative interpretation, this corresponds to an estimated hazard about 7% lower with warfarin than aspirin.
The estimate does not mean that 7% fewer patients necessarily experienced an event, nor does it describe an individual patient's probability of stroke, intracerebral hemorrhage, or death. A hazard ratio is a model-based relative measure of event hazard over follow-up.
The 95% confidence interval of 0.79–1.10 indicates substantial uncertainty around the point estimate. Because the interval includes 1, the data are compatible with both a lower and a higher estimated hazard for warfarin relative to aspirin under the specified model.
The P-value of 0.40 addresses the statistical evidence against the prespecified null hypothesis under the analysis framework. It is not a measure of effect size and does not tell us that the treatments are clinically identical. The estimate and its confidence interval are needed to understand the magnitude and precision of the comparison.
Because the analysis uses a Cox model, interpretation also depends on the model's proportional-hazards framework. Censoring and follow-up contribute to the time-to-event analysis, and the stratification factors affect how the hazard comparison is estimated.
7. Secondary Result: Composite of Heart Failure Hospitalization, Myocardial Infarction, Stroke, Intracerebral Hemorrhage, or Death
The secondary composite extended the event definition to include hospitalization for heart failure and myocardial infarction in addition to ischemic stroke, intracerebral hemorrhage, and death.
Secondary composite hazard ratio
95% CI: 0.93–1.23 · P = 0.33
Warfarin vs aspirin; intention-to-treat analysis; Cox proportional-hazards model
| Secondary endpoint statistic | Reported value |
|---|---|
| Effect measure | Hazard ratio |
| Comparison | Warfarin vs aspirin |
| Estimate | 1.07 |
| 95% confidence interval | 0.93–1.23 |
| P-value | 0.33 |
| Analysis population | Intent-to-treat: all enrolled patients were analyzed |
| Model | Cox proportional-hazards model |
| Stratification | Site; NYHA class (I vs. II-IV); recent stroke or TIA status |
The hazard ratio of 1.07 places the estimated hazard for the warfarin group at 1.07 times that of the aspirin group for the secondary composite. The point estimate therefore corresponds to an estimated hazard about 7% higher with warfarin under the fitted model.
The 95% confidence interval of 0.93–1.23 spans 1. This means the statistical uncertainty includes values consistent with either a modestly lower or a higher hazard for warfarin. The interval is more informative about that uncertainty than the P-value alone.
The P-value of 0.33 does not quantify the size or clinical importance of the observed 1.07 estimate. It summarizes the evidence against the prespecified null hypothesis under the stated testing framework.
This is a time-to-event comparison rather than a simple comparison of the proportion of patients who eventually experienced an event. Censoring, follow-up time, stratification, and the Cox-model assumptions therefore remain relevant to interpretation.
8. Individual Component Results
The registry also posted analyses of individual components of the primary and secondary composites. These analyses used intention-to-treat populations and cause-specific Cox models stratified by site, NYHA class, and prior stroke or TIA status.
| Endpoint | HR, Warfarin vs aspirin | 95% CI | P-value |
|---|---|---|---|
| Ischemic stroke, primary composite component | 0.52 | 0.33–0.82 | 0.005 |
| Intracerebral hemorrhage, primary composite component | 2.22 | 0.43–11.66 | 0.35 |
| Death, primary composite component | 1.01 | 0.85–1.20 | 0.91 |
| Myocardial infarction, secondary composite component | 0.98 | 0.58–1.64 | 0.93 |
| Heart failure hospitalization, secondary composite component | 1.21 | 0.998–1.47 | 0.053 |
| Ischemic stroke, secondary composite component | 0.55 | 0.32–0.96 | 0.03 |
| Intracerebral hemorrhage, secondary composite component | 1.77 | 0.32–9.88 | 0.51 |
| Death, secondary composite component | 1.03 | 0.81–1.30 | 0.83 |
How to interpret the component pattern
The individual estimates illustrate why composite endpoints require component-level context. The ischemic-stroke analyses have hazard-ratio estimates below 1, whereas the intracerebral-hemorrhage estimates are above 1. The confidence intervals for the hemorrhage estimates are very wide, reflecting substantial uncertainty in those component-specific comparisons.
The ischemic-stroke estimate of 0.52 corresponds to an estimated hazard approximately 48% lower with warfarin than aspirin under the cause-specific Cox model. Its 95% CI of 0.33–0.82 indicates that the point estimate is considerably below 1, while still quantifying uncertainty around the magnitude of the effect.
By contrast, the intracerebral-hemorrhage estimate of 2.22 has a 95% CI of 0.43–11.66. The very wide interval means that the point estimate alone provides an incomplete description of the evidence. The data are compatible with a substantially lower or substantially higher hazard under the fitted model.
The P-values of 0.005 for ischemic stroke and 0.35 for intracerebral hemorrhage should not be interpreted as measurements of the relative size of the effects. P-values and hazard ratios answer different questions.
9. Other Prespecified Time-to-Event Results
| Endpoint | HR | 95% CI | P-value | Interpretive direction |
|---|---|---|---|---|
| Ischemic stroke | 0.52 | 0.33–0.82 | 0.005 | Lower estimated hazard with warfarin |
| Intracerebral hemorrhage | 2.22 | 0.43–11.66 | 0.35 | Higher point estimate with warfarin; wide uncertainty |
| Death | 1.01 | 0.85–1.20 | 0.91 | Near-null point estimate |
| Myocardial infarction | 0.98 | 0.58–1.64 | 0.93 | Near-null point estimate |
| Heart failure hospitalization | 1.21 | 0.998–1.47 | 0.053 | Higher point estimate with warfarin |
| Ischemic stroke, secondary composite | 0.55 | 0.32–0.96 | 0.03 | Lower estimated hazard with warfarin |
| Intracerebral hemorrhage, secondary composite | 1.77 | 0.32–9.88 | 0.51 | Higher point estimate with warfarin; wide uncertainty |
| Death, secondary composite | 1.03 | 0.81–1.30 | 0.83 | Near-null point estimate |
These endpoints were prespecified and were analyzed with the same general cause-specific Cox framework. They should nevertheless be interpreted as distinct endpoints rather than as interchangeable estimates of a single treatment effect.
10. Hemorrhage Rate Results
Major and minor hemorrhage were analyzed differently from the time-to-first-event composite endpoints. The registry reports Poisson regression with rate ratios, using the warfarin group as numerator and aspirin as denominator.
Major Hemorrhage
Major hemorrhage rate ratio
95% CI: 1.36–3.12 · P < 0.001
Warfarin vs aspirin; intention-to-treat; Poisson regression
A rate ratio of 2.05 means that the reported major-hemorrhage event rate per patient-time was estimated to be 2.05 times as high in the warfarin group as in the aspirin group. As a simple relative interpretation, the estimated rate was approximately 105% higher with warfarin.
The 95% CI of 1.36–3.12 describes uncertainty around that rate-ratio estimate. Unlike a hazard ratio, this quantity is specifically a comparison of event rates expressed over accumulated patient-time.
The P-value of <0.001 indicates strong statistical evidence against the prespecified null hypothesis of no difference in the rate comparison. It does not mean that the probability of a major hemorrhage for an individual patient was <0.001 or that the effect size was <0.001.
Minor Hemorrhage
Minor hemorrhage rate ratio
95% CI: 1.34–1.81 · P < 0.001
Warfarin vs aspirin; intention-to-treat; Poisson regression
The rate ratio of 1.56 indicates that the reported minor-hemorrhage event rate was estimated to be 1.56 times the aspirin-group rate in the warfarin group. This corresponds to an estimated rate approximately 56% higher with warfarin.
The confidence interval of 1.34–1.81 provides a relatively narrower range around the estimated rate ratio than the major-hemorrhage estimate. The interval remains entirely above 1.
Again, the P-value of <0.001 is evidence against a null rate ratio of 1 under the specified model. It is not a measure of the clinical magnitude of the increased event rate.
11. Serious Adverse Events
The registry reports serious adverse events by randomized arm as affected patients divided by patients at risk.
| Arm | Affected / at risk |
|---|---|
| Aspirin | 617 / 1,163 |
| Warfarin | 632 / 1,142 |
These counts describe the number of patients affected among those at risk in each arm. They are not the same statistical quantity as the primary time-to-event hazard ratio or the hemorrhage rate ratios, so they should not be directly substituted for those effect measures.
12. Statistical Methods Explained
Why was a Cox proportional-hazards model used?
The primary endpoint was defined by the time from randomization to the first occurrence of an event, with follow-up extending up to 6 years. A Cox model is designed for this type of time-to-event outcome because it uses both event occurrence and the timing of follow-up while accommodating censored observations.
What does the primary hazard ratio of 0.93 mean?
Because the registry defines warfarin as the numerator and aspirin as the denominator, an HR of 0.93 represents an estimated instantaneous event hazard in the warfarin group that is 0.93 times the aspirin-group hazard under the fitted model. It does not mean that the probability of experiencing the composite endpoint was exactly 7% lower for every patient.
Why were the Cox models stratified?
The registry specifies stratification by site, NYHA class, and recent stroke or TIA status. Stratification allows the baseline hazard to differ across these strata while estimating the treatment comparison within the Cox framework. This is different from simply ignoring those factors.
Why are individual components analyzed separately?
A composite endpoint combines clinically distinct events. Separate component analyses show how the treatment comparison behaves for ischemic stroke, intracerebral hemorrhage, death, myocardial infarction, and heart failure hospitalization. Component estimates can differ substantially even when they contribute to the same composite endpoint.
Why was Poisson regression used for hemorrhage?
Major and minor hemorrhage were expressed as rates per 100 patient-years, making accumulated patient-time part of the outcome definition. Poisson regression is a standard model for count data observed over differing amounts of exposure time, and the resulting rate ratio compares event rates between the randomized groups.
Why is a rate ratio different from a hazard ratio?
A hazard ratio compares instantaneous event hazards within a time-to-event model. A rate ratio compares event rates per unit of accumulated patient-time. Although both are relative measures, they are not numerically interchangeable and should be interpreted according to the model and endpoint that produced them.
What does a wide confidence interval for intracerebral hemorrhage mean?
The primary-composite intracerebral-hemorrhage analysis has an HR of 2.22 with a 95% CI of 0.43–11.66. The width of that interval indicates substantial uncertainty about the magnitude and even the direction of the underlying hazard comparison. A point estimate should therefore not be interpreted without its confidence interval.
13. Primary Sample-Size and Power Considerations
The original target sample size was 2,860, described as providing 89% power for a log-rank test with two-sided alpha .05, assuming a hazard-rate reduction of 17.82% in either group compared with the other. The assumptions also allowed for beta-blocker use, discontinuation of therapy, dropout, and crossover.
The final sample of 2,305 patients yielded 69% power under the registry's stated analysis notes.
Original target
2,860 patients and 89% power for the specified log-rank design assumptions.
Final sample
2,305 patients and 69% power under the stated final-sample calculation.
Alpha
Two-sided alpha .05 for the original log-rank power calculation.
Assumed effect
Hazard-rate reduction of 17.82% in either group compared with the other.
Power is a design quantity: it describes the probability of detecting a specified effect under specified assumptions. It is not a measure of the observed treatment effect and should not be interpreted from the final P-value.
14. Stratification and Covariate Adjustment
The primary Cox analysis was stratified by three factors: site, New York Heart Association class with class I versus II-IV, and status with respect to recent stroke or transient ischemic attack.
| Stratification factor | Specified categories | Statistical role |
|---|---|---|
| Site | Site-specific strata | Allows baseline hazard to vary by site while estimating the treatment comparison. |
| NYHA class | I vs. II-IV | Accounts for this prespecified clinical classification in the stratified survival model. |
| Recent stroke or TIA status | Status with respect to recent stroke or TIA | Allows the treatment comparison to be estimated within prespecified strata defined by this status. |
The registry's primary analysis notes also identify covariate adjustment and beta-blocker use in the original sample-size assumptions. Stratification and covariate adjustment are related but distinct ideas: stratification permits separate baseline hazards across strata, whereas covariate adjustment generally incorporates covariates directly into a regression model.
15. Competing Risks and Cause-Specific Cox Models
The individual ischemic-stroke and intracerebral-hemorrhage analyses were described as cause-specific Cox models. This matters because patients can experience other clinically relevant events before the event of interest.
For example, the ischemic-stroke analysis adjusts for competing risks of death and intracerebral hemorrhage according to the registry's analysis note. The resulting hazard ratio is a cause-specific hazard comparison, not a direct comparison of cumulative incidence probabilities.
This distinction is particularly important for clinical endpoints that compete with death. A cause-specific HR and a cumulative-incidence comparison answer different statistical questions.
16. Composite Endpoints: What the Primary Result Combines
The primary endpoint combines three events: ischemic stroke, intracerebral hemorrhage, and death. A patient contributes the time from randomization until the first of these events occurs.
| Component | Primary composite role | Separate HR |
|---|---|---|
| Ischemic stroke | Component of primary composite | 0.52 (95% CI 0.33–0.82) |
| Intracerebral hemorrhage | Component of primary composite | 2.22 (95% CI 0.43–11.66) |
| Death | Component of primary composite | 1.01 (95% CI 0.85–1.20) |
The composite HR of 0.93 should not be treated as if it were an average of the three component hazard ratios. The composite is a separate time-to-first-event endpoint, and its estimate reflects the combined event process defined by the protocol.
17. Interpreting the P-values
The registry reports two-sided P-values for the posted analyses. These values quantify the evidence against the corresponding null hypotheses within the specified statistical models; they do not measure the magnitude of an effect.
| Endpoint | Estimate | P-value | What the P-value addresses |
|---|---|---|---|
| Primary composite | HR 0.93 | 0.40 | Evidence against the primary null hypothesis of no significant difference in time to first composite event. |
| Secondary composite | HR 1.07 | 0.33 | Evidence against the secondary null hypothesis of no significant difference in time to first secondary-composite event. |
| Ischemic stroke | HR 0.52 | 0.005 | Evidence against the corresponding cause-specific null hypothesis. |
| Major hemorrhage | Rate ratio 2.05 | <0.001 | Evidence against the corresponding rate-comparison null hypothesis. |
| Minor hemorrhage | Rate ratio 1.56 | <0.001 | Evidence against the corresponding rate-comparison null hypothesis. |
The table illustrates why P-values should be read alongside effect estimates and confidence intervals. A small P-value can accompany a modest effect, while a larger P-value can accompany a large point estimate when the estimate is imprecise.
18. Results Across Endpoint Families
This visual is intentionally a conceptual display of the reported point estimates rather than a forest plot. The hazard ratios and rate ratios belong to different endpoint definitions and different regression families, so they should not be interpreted as a single common scale of treatment benefit or harm.
19. Statistical Interpretation of the Primary Endpoint
The primary HR of 0.93 is close to 1, indicating that the fitted model estimated relatively similar instantaneous hazards for the primary composite between warfarin and aspirin.
The 95% CI of 0.79–1.10 shows that the point estimate has meaningful statistical uncertainty. The interval extends on both sides of 1, so the estimate does not establish a precise direction of the treatment effect at the conventional two-sided 95% confidence level.
The 0.40 P-value is not an effect-size statistic. It quantifies the evidence against the prespecified primary null hypothesis under the Cox-model analysis framework.
The primary result does not establish that warfarin and aspirin have identical effects for every component, every patient, or every point in follow-up. It describes the estimated treatment comparison for the prespecified composite time-to-event endpoint.
20. Statistical Interpretation of the Hemorrhage Findings
The hemorrhage analyses illustrate a different endpoint structure from the primary composite. Major and minor hemorrhage were evaluated using patient-time rates and Poisson regression.
| Endpoint | Rate ratio | 95% CI | P-value |
|---|---|---|---|
| Major hemorrhage | 2.05 | 1.36–3.12 | <0.001 |
| Minor hemorrhage | 1.56 | 1.34–1.81 | <0.001 |
Both point estimates are above 1, and both reported confidence intervals are entirely above 1. The statistical interpretation is therefore different from the primary composite analysis, where the confidence interval includes 1.
Importantly, these are rate ratios, not hazard ratios. The major- and minor-hemorrhage findings should therefore be described as differences in reported event rates per patient-time rather than as instantaneous hazard comparisons.
21. Limitations
- Composite endpoint interpretation: the primary outcome combines ischemic stroke, intracerebral hemorrhage, and death, which are distinct clinical events with different individual hazard estimates.
- Component-specific precision: the intracerebral-hemorrhage analyses have very wide confidence intervals, particularly the primary-composite component estimate of 2.22 with a 95% CI of 0.43–11.66.
- Different estimands across analyses: the primary and component outcomes use Cox hazard ratios, whereas major and minor hemorrhage use Poisson rate ratios.
- Proportional-hazards interpretation: Cox-model hazard ratios are model-based relative measures and require care when translating a single HR into a description of risk over an entire follow-up period.
- Competing events: cause-specific analyses of individual outcomes require careful distinction between cause-specific hazards and cumulative event probabilities.
- Power: the original target sample was 2,860 patients with 89% power under the specified assumptions, while the final sample of 2,305 yielded 69% power under the registry's stated calculation.
- Serious adverse events: the registry reports affected and at-risk counts by arm, but these counts are not equivalent to a time-to-event hazard ratio or a patient-time rate ratio.
- Follow-up: the endpoint definitions allow follow-up for up to 6 years, but the registry endpoint descriptions should not be interpreted as supplying a common fixed follow-up time for every patient.
22. Why This Trial Matters Statistically
WARCEF is a useful teaching case because the registry combines randomized treatment assignment with several related but statistically distinct endpoint frameworks. The primary endpoint is a time-to-first-event composite, individual components are evaluated with cause-specific Cox models, and hemorrhage outcomes are evaluated as patient-time rates using Poisson regression.
| Concept | How it appears in WARCEF |
|---|---|
| Randomization | Patients were randomized to aspirin or warfarin. |
| Double masking | The registry describes the trial as double-masked. |
| Intention-to-treat analysis | All enrolled patients were analyzed for the posted primary analysis. |
| Time-to-event endpoint | The primary outcome measured time from randomization to the first composite event. |
| Cox proportional-hazards model | Used for the primary, secondary, and component time-to-event analyses. |
| Hazard ratio | Used to compare warfarin with aspirin for time-to-event outcomes. |
| Stratified analysis | Cox models were stratified by site, NYHA class, and recent stroke/TIA status. |
| Cause-specific analysis | Individual components were analyzed with cause-specific Cox models. |
| Poisson regression | Used for major and minor hemorrhage rates. |
| Rate ratio | Used to compare hemorrhage rates between randomized groups. |
| Confidence intervals | 95% confidence intervals accompany the posted effect estimates. |
| Power | The final sample size was associated with 69% power under the stated calculation. |
23. Statistical Methods Explained in Context
Hazard ratio vs rate ratio
The primary endpoint uses a hazard ratio from a Cox model, whereas hemorrhage uses a rate ratio from Poisson regression. The two measures summarize different statistical quantities.
Composite vs component
The composite HR of 0.93 should not be interpreted as an average of the individual component HRs. The composite is its own time-to-first-event endpoint.
Cause-specific hazards
For individual outcomes such as ischemic stroke, the cause-specific Cox model evaluates the event of interest while accounting for other event types within the risk-set definition.
Confidence intervals
The width of the confidence interval conveys precision. The very wide interval for intracerebral hemorrhage indicates substantially more uncertainty than the narrower interval for major hemorrhage.
24. Related Tutorials
Learn more about the methods used in this trial:
25. Related Calculators
26. Sources
- ClinicalTrials.gov: NCT00041938 — WARCEF.
- PubMed: PMID 38393500.
- PubMed: PMID 38205865.
- PubMed: PMID 31779926.
- PubMed: PMID 28774396.
- PubMed: PMID 27354224.
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27. Record Summary
WARCEF provides a compact example of how a randomized clinical trial can require several complementary statistical analyses. The primary endpoint is a time-to-first-event composite analyzed with a stratified Cox proportional-hazards model. The registry also reports a secondary composite and individual component analyses using cause-specific Cox models, while major and minor hemorrhage are analyzed as patient-time rates using Poisson regression.
The primary composite estimate was HR 0.93 with a 95% CI of 0.79–1.10 and P = 0.40. The individual ischemic-stroke analysis produced an HR of 0.52 (95% CI 0.33–0.82; P = 0.005), while the intracerebral-hemorrhage component had an HR of 2.22 (95% CI 0.43–11.66; P = 0.35). The hemorrhage rate analyses produced rate ratios of 2.05 for major hemorrhage and 1.56 for minor hemorrhage, each with P < 0.001.