This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Sleep Apnea Treatment After Stroke (SATS) (NCT00282815), a randomized phase 2 study. The primary outcome is Cumulative Continuous Positive Airway Pressure (CPAP)/Sham CPAP Usage Hours Over the 3 Month Period..
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00282815 |
| Phase | Phase 2 |
| Condition | Obstructive Sleep Apnea, Stroke |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Double |
| Enrollment | 32 |
| Arms in the primary outcome | 2 |
| Lead sponsor | University of Michigan |
| Results posted | Yes |
2. Clinical Question
Population
People with stroke and obstructive sleep apnea were the intended population. The registry lists the trial enrollment as 32. The number contributing data to the primary endpoint differs by arm and is reported with the endpoint results.
Intervention
The active intervention was continuous positive airway pressure, or CPAP, a device treatment. The registry's brief summary frames the study purpose as determining whether treating obstructive sleep apnea with CPAP improves symptoms caused by stroke.
Comparator
The comparator was sham CPAP, described in the arm information as placebo. The study is listed as randomized, double-masked, and parallel, but further details about how masking was maintained are not reported in the registry record.
Primary question
The posted primary endpoint is cumulative CPAP or sham CPAP usage hours per participant over 3 months. It measures device use, not stroke symptoms. The registry also lists the Barthel Index as a secondary outcome, but secondary results are not posted.
These are related but distinct questions: whether participants used the assigned device and whether treatment changed symptoms or function. Device-use time can describe exposure to the assigned treatment, but it does not by itself establish a change in stroke symptoms. The primary endpoint is reported as a median with an inter-quartile range for each arm. The registry record does not post an inferential comparison, confidence interval, or analysis of a treatment effect for this outcome. The purpose stated in the study summary therefore extends beyond what can be concluded from the posted primary results.
3. Trial Design
The registry identifies Sleep Apnea Treatment After Stroke (SATS), NCT00282815, as a phase 2 randomized, double-masked, parallel study sponsored by the University of Michigan. It lists obstructive sleep apnea and stroke as the conditions under study. The record gives a start of 2004-09, a primary completion date of 2010-05, and a status of terminated. A reason for termination is not reported in the registry record.
The assigned treatments were active CPAP and sham CPAP. The record describes sham CPAP as placebo, but does not give further information about the device setup, treatment duration beyond the primary endpoint timeframe, or procedures used to keep participants and study personnel masked. Random allocation and double masking are registry design labels; the method used to generate the allocation sequence, conceal assignments, or assess masking success is not reported in the registry record.
Registry enrollment is listed as 32. The primary endpoint results use 8 participants in the active CPAP arm and 10 in the sham CPAP arm. The endpoint description says data were unavailable for one sham participant, lowering the sham group count from 11 to 10. The reason for the available active-arm endpoint count and a full participant flow are not reported in the registry record. These differing counts should not be treated as interchangeable: enrollment, endpoint availability, and safety denominators describe different recorded information.
The registry lists three outcome measures and identifies the Barthel Index as a secondary outcome. It records no posted analyses. Details of the planned statistical methods, follow-up procedures, and analysis populations are not reported in the registry record. The listed design features describe how the trial was classified, but do not fill in those missing protocol details.
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
| Stage | Active Continuous Positive Airway Pressure (CPAP) | Sham Continuous Positive Airway Pressure (CPAP) |
|---|---|---|
| STARTED | 15 | 17 |
| COMPLETED | 8 | 11 |
| NOT COMPLETED | 7 | 6 |
Analysis population for the primary outcome, as defined in the registry: Data not available on one sham participant (lowering n from 11 to 10 in the shame group).
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.
| Characteristic | Unit | Active Continuous Positive Airway Pressure (CPAP) | Sham Continuous Positive Airway Pressure (CPAP) | Total |
|---|---|---|---|---|
| Participants analysed | 15 | 17 | 32 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 8 | 5 | 13 |
| Age, Categorical: >=65 years | Participants | 7 | 12 | 19 |
| Age Continuous | years | 61 (SD 16) | 74 (SD 16) | 65 (SD 16) |
| Sex: Female, Male: Female | Participants | 10 | 4 | 14 |
| Sex: Female, Male: Male | Participants | 5 | 13 | 18 |
| Region of Enrollment: United States | participants | 15 | 17 | 32 |
6. Primary Endpoint
The registry lists the primary outcome as Cumulative Continuous Positive Airway Pressure (CPAP)/Sham CPAP Usage Hours Over the 3 Month Period., measured over 3 months.
| Element | Registry entry |
|---|---|
| Result type | Median |
| Measure of spread | Inter-Quartile Range |
| Unit | Hours/participant |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is cumulative CPAP or sham CPAP usage hours per participant over 3 months. It is reported in hours per participant as a median and inter-quartile range. In the active CPAP arm, the median is 53.0 hours, with an inter-quartile range from 22.0 to 173.0 hours. In the sham CPAP arm, the median is 74.0 hours, with an inter-quartile range from 17.0 to 94.0 hours. The endpoint counts are 8 and 10, respectively.
Device-use time is a measure of exposure to the assigned device. In general, documenting exposure can help characterize whether participants used an intervention during the study. It does not directly measure stroke-related symptoms, functional status, or the effect of treatment on those outcomes. The registry's brief summary mentions symptoms as the study purpose, while the posted primary endpoint is device use. The record does not explain why this endpoint was selected as primary or how it was expected to relate to the clinical outcomes.
A median describes the center of the observed values, while the inter-quartile range describes the middle portion of their distribution. These summaries are useful when individual values vary and a mean may not adequately represent a typical observation. They do not show every participant's use or quantify uncertainty in a comparison between arms. No confidence interval or statistical test for the primary endpoint is reported in the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The posted primary result is a pair of arm-specific summaries of cumulative device use. The active CPAP arm has a median of 53.0 hours and an inter-quartile range of 22.0 to 173.0 hours; the sham CPAP arm has a median of 74.0 hours and an inter-quartile range of 17.0 to 94.0 hours. These values describe observed use over 3 months among the participants included in each endpoint summary. They do not establish whether the difference between arms is statistically distinguishable from chance or clinically important.
The ranges indicate variation among participants within each arm. In the active arm, the upper end of the inter-quartile range is substantially farther from the median than the lower end; in the sham arm, the median lies within a more compact reported interval. Such patterns can occur when usage is unevenly distributed. They are descriptive features, not evidence about why individual participants used the device as they did. The registry does not report individual values or an explanation for the observed variation.
The available endpoint counts are 8 for active CPAP and 10 for sham CPAP. The endpoint description separately notes unavailable usage data for one sham participant, reducing that arm's count from 11 to 10. The record does not explain the difference between the enrollment of 32 and the endpoint counts, or provide a full account of participant flow. Without further information, the posted summaries should be interpreted as results among the participants with endpoint data rather than as a complete account of all enrolled participants.
No inferential analysis of the primary endpoint is posted. A comparison of medians alone does not provide a standard error, confidence interval, or p-value. It is therefore not possible to assess the precision of an arm contrast from these summaries, or to determine whether the observed medians are compatible with a range of treatment effects. The registry record also does not report an adjusted analysis, a prespecified analysis model, or a primary treatment-effect estimate.
The registry lists the Barthel Index as a secondary outcome, but does not post its results. It lists three outcome measures and no analyses. Consequently, the available record cannot answer whether device use was associated with a change in stroke symptoms or function. The posted usage summaries describe device exposure; they should not be substituted for results on clinical outcomes.
The status is terminated, but the reason for termination is not reported in the registry record. The status alone does not show whether the trial stopped early, whether the planned enrollment was reached, or whether any particular result influenced the decision. Those explanations should not be inferred from the endpoint summaries.
9. Statistical Methods Explained
The registry reports medians and inter-quartile ranges for cumulative usage hours. It does not report an inferential analysis of the primary endpoint. The following points explain how to read the posted summaries in general and distinguish them from a treatment-effect analysis.
What does a median describe?
In general, the median is a measure of the center of a distribution. It is less affected by particularly high or low observations than an arithmetic mean. For a measure such as accumulated device-use hours, participant values may be unevenly distributed: some people may use a device much more or less than others. A median can therefore give a useful description of typical observed use without requiring the distribution to be symmetric.
The reported medians are 53.0 hours for active CPAP and 74.0 hours for sham CPAP over 3 months. These are summaries of observed usage in the endpoint population for each arm. They are not the mean usage, do not describe each participant, and are not by themselves an estimate with a measure of uncertainty. A numerical contrast between medians would not supply the missing uncertainty information or account for the trial design.
What does the inter-quartile range add?
In general, the inter-quartile range spans the middle portion of the observed distribution. It describes how spread out the central observations are, while leaving the most extreme observations outside that interval. The active CPAP result has an inter-quartile range of 22.0 to 173.0 hours; the sham CPAP result has an inter-quartile range of 17.0 to 94.0 hours.
An inter-quartile range is not a confidence interval for the median or for the difference between treatment arms. It describes variation among observed participants rather than the precision of an estimated treatment effect. Overlap or separation between two such ranges is not a substitute for a formal comparison. The registry does not report a confidence interval for either median or for an arm contrast.
Why would an analysis model matter?
In general, an inferential analysis uses a statistical model or test to quantify how compatible the observed data are with a specified comparison. The choice depends on the endpoint's distribution, the study design, and the question the analysis is intended to answer. Usage hours can be highly variable, and a small number of participants with high values can affect some methods more than others. A method based only on a normal distribution may be unsuitable if its assumptions do not reflect the data. The registry record does not identify a model or test for the primary endpoint, nor does it report checks of model assumptions.
General methods for strongly variable or over-dispersed data can allow variability beyond that expected under a simpler model. That is a general consideration, not a claim that a particular method was used in this trial. No distributional assessment or alternative analysis is reported in the registry record. The posted median and inter-quartile range are descriptive and do not reveal which inferential method, if any, would have been appropriate.
What can randomization contribute?
In general, random allocation aims to make treatment groups comparable with respect to factors that could affect outcomes, including factors not measured by investigators. It supports a fair comparison when the allocation process is implemented as planned and outcomes are analyzed appropriately. The registry labels this study randomized, but does not report the allocation method, concealment procedures, baseline characteristics, or a treatment-effect analysis. The design label alone cannot show whether the groups were balanced in this particular trial or quantify uncertainty in the primary result.
Double masking can, in general, reduce the influence of expectations on participants' behavior and outcome assessment. The record labels the trial double-masked but does not say who was masked, how the sham device was made similar to active treatment, or whether masking was assessed. These details matter for interpreting device-use behavior, since participants' knowledge or beliefs could affect use. They are not documented in the registry record.
What do the planning illustrations mean?
The registry describes planning illustrations based on the observed effect, a two-sided significance level of 0.05, equal allocation, and a normal approximation. It specifies that the illustrations consider detecting a stated fraction of the observed effect. These are planning assumptions, not the trial's original design justification and not observed power. The registry record does not report the trial's own sample-size justification or the values of the planning illustrations in the registry record for this analysis. A planning illustration cannot establish that the completed study had adequate precision, and it does not replace a confidence interval for the observed result.
The distinction is important: observed data summarize what happened among participants with results, while a planning calculation describes assumptions for a hypothetical design. Neither a sample-size illustration nor the fact that the study is phase 2 provides evidence of a treatment effect. Since no inferential analysis is posted for the primary endpoint, the most defensible interpretation remains descriptive.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists three outcome measures and identifies the Barthel Index as a secondary outcome. It does not post results for that secondary outcome, and it records no analyses. The status of the other listed outcome measures and any associated findings is not reported in the registry record. With several outcomes, interpretation can depend on which outcomes were designated primary, how many comparisons were planned, and whether adjustments for multiple testing were intended. The record does not report a multiplicity strategy, so it is not possible to determine how the potential for multiple comparisons was addressed.
The primary endpoint description notes that usage data were unavailable for one sham participant, with the reported count lowering from 11 to 10. The posted endpoint counts are 8 for active CPAP and 10 for sham CPAP. The reason that data are unavailable, whether missingness was related to device use or participant characteristics, and how missing observations were handled are not reported in the registry record. No imputation method or sensitivity analysis is reported.
The record does not specify whether the primary analysis followed an intention-to-treat principle, included only participants who used their assigned device, or used another analysis population. It also does not provide a participant-flow account explaining the relationship between enrollment and endpoint availability. Accordingly, the posted summaries should be read as summaries for their stated endpoint counts, not as proof that all enrolled participants were included in the primary analysis.
Such omissions limit assessment of bias and robustness. They do not establish that missing data or multiplicity changed the results; they mean that the registry record does not provide the information needed to evaluate those possibilities.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Active Continuous Positive Airway Pressure (CPAP) | 0 | 15 | 0.0% |
| Sham Continuous Positive Airway Pressure (CPAP) | 0 | 17 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 5% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Active Continuous Positive Airway Pressure (CPAP) | 0 of 15 |
| Sham Continuous Positive Airway Pressure (CPAP) | 0 of 17 |
The registry reports serious adverse events for the active CPAP and sham CPAP groups. For active CPAP, 15 participants are listed as at risk and 0 as affected by serious adverse events. For sham CPAP, 17 participants are listed as at risk and 0 as affected. The record also reports 0 participants affected by other adverse events in each group, with 15 and 17 at risk, respectively.
These figures are counts recorded in the registry, not estimates that an event is impossible. A zero reported count means no affected participants are listed for that category in the stated group; it does not show that the treatment has no risk. The safety denominators differ from the primary endpoint counts and should not be treated as the same analysis population. The registry does not report death counts; the death entries are not reported in the registry record.
The record does not provide event narratives, severity details beyond the serious-event classification, timing, attribution, or a safety comparison analysis. It also does not explain the relationship between participants at risk for safety reporting and those contributing primary endpoint data. These safety figures therefore describe what was posted, but do not support a broad conclusion about comparative safety.
12. What the Result Does, and Does Not, Mean
The posted primary results show the distribution summaries of device-use hours for participants with endpoint data in the active CPAP and sham CPAP arms. The medians are 53.0 hours and 74.0 hours, respectively, over 3 months. The inter-quartile ranges are 22.0 to 173.0 hours and 17.0 to 94.0 hours. These statistics describe use; they are not direct measurements of stroke symptoms or functional recovery.
The trial's brief summary says its purpose was to determine whether treating obstructive sleep apnea after stroke with CPAP would improve symptoms caused by stroke. The primary endpoint posted in the registry is cumulative usage, and results for the listed secondary outcome, the Barthel Index, are not posted. The record therefore does not provide the outcome evidence needed to determine whether symptoms or function changed.
No confidence interval, p-value, or other inferential comparison for the primary endpoint is reported. The posted medians cannot by themselves establish that the groups differed beyond what might be expected from sampling variation, nor do they quantify the precision of a treatment effect. They also cannot establish that the groups were equivalent. A lack of a posted inferential result is not evidence of no effect.
The trial is listed as terminated, but the reason is not reported in the registry record. The record does not establish whether the termination related to recruitment, resources, safety, efficacy, or another reason. It would be inappropriate to infer the circumstances or their implications from the termination label alone.
In short, the available information supports a descriptive account of device use and posted adverse-event counts. It does not support a conclusion about clinical benefit, lack of benefit, or comparative safety. The distinction between a device-use endpoint and a clinical outcome is central to interpreting this record.
13. Why This Trial Matters Statistically
This trial illustrates why endpoint choice matters in clinical research. The stated study purpose concerns possible improvement in symptoms caused by stroke, while the posted primary endpoint measures cumulative use of CPAP or sham CPAP. Usage is relevant as a measure of exposure, but it is not itself a symptom or functional outcome. Statistical interpretation needs to stay aligned with what the endpoint actually measures.
It also demonstrates the difference between descriptive summaries and inferential evidence. A median and inter-quartile range convey the center and spread of observed usage. They do not provide a confidence interval or a test of the treatment comparison. Readers should not treat the visual or numerical contrast between arm summaries as if it were a fully analyzed treatment effect.
Missing information matters for evaluating the reliability of a result. The registry identifies unavailable sham-arm usage data and gives endpoint counts, but does not explain missingness or specify the analysis population. Those details are necessary to assess how well the reported summaries represent the randomized groups. The different safety denominators further reinforce that endpoint and safety counts describe distinct recorded populations.
Finally, the registry lists additional outcomes but does not post their analyses. Without those findings, a reader cannot connect device use to the clinical questions motivating the trial or assess how multiple outcomes were handled. The record is useful for identifying the design and the available descriptive results, while also showing why prespecified methods, participant flow, and complete outcome reporting are important to sound interpretation.
14. 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 registry record is limited by the absence of a reported inferential analysis for the primary endpoint. It provides medians and inter-quartile ranges but no confidence interval, p-value, model, or treatment-effect estimate. The precision of a comparison therefore cannot be assessed from the posted usage summaries.
Participant accounting is incomplete. Enrollment is listed as 32, while the primary endpoint uses 8 active CPAP participants and 10 sham CPAP participants. The endpoint description says one sham participant's data were unavailable, lowering that group's count from 11 to 10, but the reason and the remaining participant flow are not described. The record does not report the primary analysis population or explain why the active endpoint count is 8.
The clinical outcome information is also limited. The Barthel Index is listed as a secondary outcome, but its results are not posted. The record lists three outcome measures and no analyses. It does not explain how outcomes were selected, whether multiplicity was considered, or whether results for other measures are available elsewhere in the registry record.
Details needed to evaluate conduct are not reported, including the randomization procedure, allocation concealment, masking procedures, baseline characteristics, missing-data methods, and protocol-level analysis plan. The reason the study was terminated is not reported. These omissions do not demonstrate that the conduct or results were flawed; they restrict what can be independently assessed from the registry record.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Sleep Apnea Treatment After Stroke (SATS) — NCT00282815.
- Registry record last updated 2013-03-11; status last verified 2012-12.
- Results first posted 2013-03-11.
- 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.
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18. Record Summary
NCT00282815 is a University of Michigan phase 2 randomized, double-masked, parallel trial of active CPAP versus sham CPAP in people with obstructive sleep apnea after stroke. Registry enrollment is 32. The record gives a start of 2004-09, primary completion of 2010-05, and status of terminated; the reason for termination is not reported in the registry record.
The primary endpoint is cumulative device usage over 3 months, reported as medians and inter-quartile ranges. The active CPAP result is 53.0 hours, with an inter-quartile range of 22.0 to 173.0 hours, among 8 participants. The sham CPAP result is 74.0 hours, with an inter-quartile range of 17.0 to 94.0 hours, among 10 participants. The registry lists the Barthel Index as a secondary outcome but does not post its results. No inferential analyses are listed. Safety results report 0 serious adverse events and 0 other adverse events in each group; death counts are not reported in the registry record.