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
ATAC was a phase 3 randomized, double-blind, parallel-design clinical trial sub-protocol evaluating bone density outcomes. The study enrolled 308 participants and included three arms.
| Feature | ATAC |
|---|---|
| NCT ID | NCT00784940 |
| Acronym | ATAC |
| Title | ATAC - Bone Density Sub-Protocol |
| Condition | Bone Density |
| Design | Randomized, parallel, double-blind |
| Lead sponsor | AstraZeneca |
| Sponsor type | Industry |
2. Clinical Question
Population
The registry identifies the study condition as bone density and reports enrollment of 308 participants.
Intervention
Anastrozole was evaluated as a study intervention.
Comparator
Tamoxifen was listed as another drug intervention.
Primary question
The registered primary endpoints evaluated time to withdrawal and time to recurrence.
3. Trial Design
Randomized
Double
Parallel
Three-arm design
4. Registered Endpoints
| Endpoint | Registry definition |
|---|---|
| Primary endpoint | Time to withdrawal |
| Primary endpoint | Time to recurrence |
5. Planned Analysis
The ClinicalTrials.gov record lists registered primary endpoints but does not post statistical analyses or outcome estimates.
Time-to-event endpoints such as time to withdrawal and time to recurrence are typically analyzed using methods that account for follow-up over time, including survival-function estimation, comparison of event times between randomized groups, and model-based estimates such as hazard ratios when prespecified. The registry does not report the formal statistical analysis results for these endpoints.
6. Statistical Methodology
This trial design includes several foundational elements of randomized clinical-trial analysis:
Randomization
Randomization creates treatment groups intended to be comparable at baseline. The treatment comparison is therefore interpreted according to assigned intervention groups rather than patient-selected treatment.
Double masking
Double masking reduces the potential influence of expectations from participants and investigators on treatment exposure, assessment, and reporting.
Time-to-event analysis
Endpoints involving time until an event require methods that handle participants who have not yet experienced the event at the end of observation through censoring approaches.
7. Statistical Methods Explained
Why is randomization important?
Randomization helps balance measured and unmeasured factors between groups, allowing differences in outcomes to be attributed more directly to the assigned interventions.
Why are time-to-event methods used?
Some participants may not experience the endpoint during follow-up. Survival-analysis methods incorporate available follow-up while accounting for incomplete event observation.
What does a hazard ratio represent?
A hazard ratio compares estimated event rates over time between groups. It does not represent the percentage of patients who experience an event or an individual patient's probability.
Why does censoring matter?
Censoring allows participants with incomplete event information to contribute follow-up time without assuming that their future outcomes are known.
8. Limitations
- The registry does not report posted statistical analyses or endpoint results.
- Sample-size calculations, analysis populations, and missing-data procedures are not reported in the available registry record.
- Without posted results, estimates, confidence intervals, and p-values cannot be evaluated.
9. Why This Trial Matters Statistically
| Concept | Application |
|---|---|
| Randomized design | Comparison of assigned intervention groups |
| Blinding | Reduction of assessment and reporting bias |
| Parallel design | Concurrent comparison of multiple arms |
| Time-to-event endpoints | Analysis of outcomes occurring over follow-up |