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
SPACE was a completed, non-randomized, parallel diagnostic study of patients with carotid stenoses. The registry lists 266 enrolled participants and two study arms involving carotid ultrasound examination and Panorama examination.
| Feature | SPACE |
|---|---|
| Study title | Stroke and Panorama - Analyzing Carotid Endocalcifications (SPACE) |
| ClinicalTrials.gov identifier | NCT00514644 |
| Condition | Carotid Stenoses |
| Status | Completed |
| Phase | NA |
| Allocation | Non-randomized |
| Design model | Parallel |
| Masking | Single |
| Primary purpose | Diagnostic |
| Enrollment | 266 |
| Number of arms | 2 |
| Lead sponsor | Umeå University |
| Sponsor type | Other |
2. Clinical Question
The central statistical question is descriptive and diagnostic rather than therapeutic: what is the prevalence of carotid stenosis in the group examined with carotid ultrasound on the "atheroma on Panoramic examination"-indication?
Population
The registry identifies the condition under study as carotid stenoses and records 266 enrolled participants.
Diagnostic intervention
Carotid ultrasound examination is listed as one of the study interventions.
Comparator / second examination
Panorama examination is listed as the other study intervention.
Primary question
The registered primary endpoint asks for the prevalence of carotid stenosis in the group examined with carotid ultrasound on the specified Panorama-related indication.
3. Trial Design
Carotid ultrasound examination
- Intervention classification: other
- Associated with the registered prevalence endpoint
- Registry wording specifies the "atheroma on Panoramic examination"-indication
Panorama examination
- Intervention classification: other
- Included as the second study intervention
- The registry classifies the overall study as non-randomized and parallel
4. Trial Timeline
Study start
The registry records the study start date as 2007-08.
Primary completion
The registry records the primary completion date as 2009-11.
Current registry status
The study is recorded as completed.
5. Primary Endpoint
| Endpoint | Registry definition | Statistical role |
|---|---|---|
| Primary endpoint | The prevalence of carotid stenosis in the group that is examined with carotid ultrasound on the "atheroma on Panoramic examination"-indication | Primary diagnostic prevalence measure |
The wording of the endpoint is important. The target quantity is a prevalence, meaning the proportion of the specified examination group in whom carotid stenosis is identified according to the study's assessment framework. This is fundamentally different from a time-to-event endpoint such as overall survival or a comparative treatment-effect measure such as a hazard ratio.
The denominator must correspond to the group defined by the registered endpoint. A prevalence estimate is meaningful only when the numerator and denominator are defined consistently.
6. Statistical Methodology
Descriptive prevalence estimation
For a binary diagnostic finding, the most direct analysis is a proportion: the number of participants meeting the carotid-stenosis definition divided by the number of participants assessed in the endpoint population. The result can be reported as a proportion or percentage.
Because the registry endpoint is specifically phrased as a prevalence in a defined examination group, the primary statistical quantity should remain tied to that group rather than being silently generalized to all 266 enrolled participants.
Confidence intervals for a proportion
A prevalence estimate should normally be accompanied by a confidence interval. The interval quantifies sampling uncertainty around the observed proportion and is particularly useful when the number of participants contributing to the endpoint differs from overall enrollment.
Here, x is the number of participants classified as having carotid stenosis and n is the number of participants contributing to the registered prevalence endpoint.
Diagnostic interpretation
The primary endpoint is prevalence rather than sensitivity, specificity, positive predictive value, or negative predictive value. Those diagnostic accuracy measures require clearly defined reference-standard and classification information. The registry information available here does not report such measures.
Non-randomized design
The study is classified as non-randomized. Consequently, the statistical interpretation should focus on the descriptive diagnostic question defined by the endpoint rather than treating the two arms as randomized treatment groups.
Parallel design
The registry classifies the design model as parallel with two arms. A parallel structure means that the study's observations can be organized by arm, but the non-randomized allocation remains important when interpreting any difference between those arms.
7. Statistical Methods Explained
What does prevalence measure?
Prevalence is the proportion of a defined population that has a condition or finding at the relevant assessment. In this study, the registered primary endpoint specifically targets the prevalence of carotid stenosis in the group receiving carotid ultrasound for the stated indication.
Why is the denominator important?
A prevalence estimate is inseparable from its denominator. The registry reports overall enrollment of 266, but the primary endpoint is defined for a particular examination group. Therefore, overall enrollment should not automatically be substituted for the endpoint denominator.
Why report a confidence interval?
A point estimate alone does not communicate statistical precision. A confidence interval provides a range of values compatible with the observed sample under the selected statistical framework. Wider intervals indicate greater uncertainty, while narrower intervals indicate greater precision.
Why is this not a hazard-ratio analysis?
The primary endpoint is a prevalence rather than a time-to-event outcome. There is no event-time dimension in the registered endpoint. Kaplan-Meier estimation and Cox proportional-hazards modeling are therefore not the natural primary methods for this question.
What does non-randomized allocation change?
Randomization is a mechanism for balancing measured and unmeasured characteristics between study groups in expectation. Because SPACE is registered as non-randomized, an observed difference between the two arms would not automatically have the causal interpretation of a randomized treatment comparison.
Why should prevalence not be called diagnostic accuracy?
Prevalence answers how common the finding is in a defined group. Diagnostic accuracy asks how well one test classifies disease relative to an appropriate reference standard. Sensitivity, specificity, predictive values, and related measures require additional information that is not contained in the registered primary endpoint.
8. Planned Analysis
The registry identifies one primary endpoint: the prevalence of carotid stenosis in the group examined with carotid ultrasound on the "atheroma on Panoramic examination"-indication.
For an endpoint of this type, the principal analysis would normally report the observed proportion of participants classified as having carotid stenosis among those contributing to the specified endpoint population. A confidence interval for that proportion would provide a measure of statistical precision.
Primary quantity
A proportion representing the prevalence of carotid stenosis in the endpoint-defined examination group.
Precision
A confidence interval would ordinarily accompany the prevalence estimate to quantify sampling uncertainty.
Population definition
The analysis should use the population explicitly described in the primary endpoint rather than automatically using total enrollment as the denominator.
Interpretation
The result would describe the prevalence in the specified study population; it would not, by itself, establish a causal treatment effect.
9. Understanding a Prevalence Estimate
If a study observes x cases among n eligible participants, the estimated prevalence is x/n. The estimate describes the proportion observed in that study population.
A confidence interval describes uncertainty around the population prevalence under the statistical model used to construct it. It does not describe the range of disease status across individual participants.
A prevalence estimate does not by itself establish that the Panorama examination caused, prevented, detected, or changed the occurrence of carotid stenosis. It is a descriptive quantity tied to the population and assessment specified by the endpoint.
10. Non-Randomized Design and Statistical Interpretation
The registry's NON_RANDOMIZED allocation designation is a central feature of the statistical interpretation. In a randomized trial, random allocation creates a basis for attributing systematic differences in outcomes to the assigned intervention, subject to the usual assumptions and limitations. That logic does not automatically apply to a non-randomized study.
For SPACE, the primary endpoint is also diagnostic and prevalence-based. The appropriate emphasis is therefore on accurately defining the examination population, counting the relevant diagnostic finding, estimating the corresponding proportion, and quantifying its uncertainty.
| Feature | Statistical implication |
|---|---|
| Non-randomized allocation | Between-arm differences should not automatically be interpreted as causal treatment effects. |
| Parallel design | The registry organizes the study into two parallel arms. |
| Single masking | The registry records single masking but does not provide further masking detail here. |
| Diagnostic purpose | The principal question concerns diagnostic findings rather than therapeutic efficacy. |
| Prevalence endpoint | The primary analysis is naturally expressed as a proportion with appropriate uncertainty. |
11. What the Registry Reports About the Interventions
| Intervention | Registry classification |
|---|---|
| Carotid ultrasound examination | Other |
| Panorama examination | Other |
The registry does not provide additional intervention parameters in the information reported here. The statistical interpretation therefore remains centered on the registered primary prevalence endpoint rather than assigning unreported technical characteristics to either examination.
12. Enrollment and Study Period
| Registry feature | Reported value |
|---|---|
| Enrollment | 266 |
| Start date | 2007-08 |
| Primary completion date | 2009-11 |
| Status | Completed |
| Lead sponsor | Umeå University |
| Sponsor type | Other |
Enrollment describes the number of participants registered for the study as a whole. It should be distinguished from the denominator of the primary endpoint, because the endpoint itself identifies a particular examination group.
13. Limitations
- No posted numerical primary result: the ClinicalTrials.gov record does not report a numerical prevalence estimate, confidence interval, or p-value for the registered primary endpoint.
- Endpoint-specific denominator: the registered endpoint is defined for a particular carotid-ultrasound examination group, so overall enrollment should not automatically be treated as the endpoint denominator.
- Non-randomized allocation: differences between the two arms cannot automatically be interpreted using the causal framework of a randomized controlled trial.
- Limited diagnostic detail: the registry information available here does not report sensitivity, specificity, predictive values, likelihood ratios, or another formal diagnostic-accuracy endpoint.
- Masking detail: the study is classified as single-masked, but the registry information available here does not specify the identity of the masked party.
- Arm-specific enrollment: the registry reports two arms and overall enrollment of 266 but does not provide arm-specific enrollment counts in the information available here.
- Limited statistical specification: the registry does not provide a detailed statistical analysis plan for the primary endpoint in the posted information available here.
14. Why This Trial Matters Statistically
SPACE is useful as a statistical teaching case because it illustrates a different class of clinical-trial analysis from the large randomized treatment trials that dominate clinical research. Its primary endpoint is a prevalence measure, and its allocation is non-randomized with a diagnostic primary purpose.
| Concept | How it appears in SPACE |
|---|---|
| Prevalence estimation | The registered primary endpoint asks for the prevalence of carotid stenosis. |
| Binary outcome analysis | The endpoint naturally reduces to whether carotid stenosis is present according to the study definition. |
| Confidence intervals | A prevalence estimate should ordinarily be accompanied by an interval describing statistical precision. |
| Endpoint population | The registry defines the primary endpoint for a specified carotid-ultrasound examination group. |
| Non-randomized allocation | The two-arm design does not have the causal interpretation provided by random treatment assignment. |
| Diagnostic study design | The study's primary purpose is diagnostic rather than therapeutic. |
| Parallel design | The registry classifies the study as parallel with two arms. |
| Masking | The registry classifies the study as single-masked. |
15. Statistical Concepts in This Trial
16. Clinical Interpretation vs Statistical Interpretation
Statistical interpretation
The primary endpoint is a prevalence measure in a defined examination group. The natural statistical summary is a proportion, accompanied by an appropriate measure of uncertainty.
Clinical interpretation
The registry frames the study around carotid stenosis and two examination modalities. Any clinical interpretation of the examinations requires attention to the exact population, endpoint definition, and diagnostic framework.
17. What Is and Is Not Established by the Registered Endpoint
| Question | What the primary endpoint addresses |
|---|---|
| How common is carotid stenosis in the specified group? | Yes. This is the registered primary question. |
| What is the prevalence estimate? | Not numerically reported in the ClinicalTrials.gov record. |
| How precise is the prevalence estimate? | No confidence interval is reported in the ClinicalTrials.gov record. |
| Is the Panorama examination superior to carotid ultrasound? | Not established by the registered endpoint alone. |
| What is the sensitivity of either examination? | Not specified by the registered primary endpoint. |
| What is the specificity of either examination? | Not specified by the registered primary endpoint. |
| Was there a statistically significant treatment effect? | This is not a therapeutic treatment-effect endpoint, and no formal statistical result is posted. |
18. A Statistical Reading of the SPACE Design
The most important analytical distinction is between describing a diagnostic finding and estimating a causal treatment effect. SPACE is registered as a diagnostic study with non-randomized allocation. Its primary endpoint is therefore naturally read as a prevalence question within a specified examination group.
That distinction determines which statistical tools are appropriate. A prevalence analysis begins with a clearly defined numerator and denominator. It then reports the estimated proportion and, ideally, a confidence interval. A comparison between groups can be considered separately, but because allocation is non-randomized, such a comparison requires careful consideration of differences between the groups before it can be interpreted causally.
The registry's two-arm, parallel structure is consequently useful for organizing the observations, but it does not by itself transform the study into a randomized comparison. The primary statistical story remains anchored to the registered diagnostic endpoint.
19. Missing Information That Affects Statistical Interpretation
The ClinicalTrials.gov record identifies the study design and primary endpoint but does not provide several pieces of information that would ordinarily be needed for a complete numerical analysis of the endpoint.
| Information | Registry status |
|---|---|
| Numerical prevalence result | Not reported |
| Confidence interval for prevalence | Not reported |
| Primary endpoint p-value | Not reported |
| Arm-specific enrollment | Not reported in the available registry data |
| Detailed statistical analysis plan | Not reported in the available registry data |
| Sensitivity / specificity | Not reported as the registered primary endpoint |
| Diagnostic reference standard | Not specified in the available registry data |
These distinctions matter because the validity of a diagnostic statistical conclusion depends on the exact endpoint population, disease classification, reference framework, and analysis population.
20. Summary of the Statistical Framework
This framework matches the registered primary endpoint more directly than a survival-analysis or randomized-treatment framework.
The registered study structure can therefore be understood as follows: SPACE enrolled 266 participants, used two parallel study arms, was non-randomized and single-masked, and had a diagnostic primary purpose. The primary endpoint focused on the prevalence of carotid stenosis in the group examined with carotid ultrasound on the specified Panorama-related indication.
21. Sources
- ClinicalTrials.gov: SPACE, NCT00514644.
- PubMed: PubMed record associated with the study.
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22. Record Summary
SPACE is a completed diagnostic study of carotid stenoses with 266 enrolled participants, two parallel arms, non-randomized allocation, and single masking. Its registered primary endpoint is the prevalence of carotid stenosis in the group examined with carotid ultrasound on the "atheroma on Panoramic examination"-indication.
Statistically, the endpoint is most naturally understood as a prevalence proportion rather than a time-to-event or therapeutic treatment-effect measure. A complete numerical interpretation would require the number of participants meeting the carotid-stenosis definition and the number contributing to the specified endpoint population, together with an appropriate confidence interval. Those numerical primary results and formal statistical analyses are not posted in the ClinicalTrials.gov record.