Study to Assess the Changes in Blood Clotting Factors and Blood Vessel Wall Function in Obstructive Sleep Apnea: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Study to Assess the Changes in Blood Clotting Factors and Blood Vessel Wall Function in Obstructive Sleep Apnea (NCT00936481), a registered phase not stated study. The primary outcome is Comparison of Levels of Mean PAI-1 Activity in Patients With Obstructive Sleep Apnea and Controls..

2. Clinical Question

3. Trial Design

The registry identifies this study as a completed investigation of obstructive sleep apnea, titled Study to Assess the Changes in Blood Clotting Factors and Blood Vessel Wall Function in Obstructive Sleep Apnea. Its official title is Variability of Fibrinolytic Markers and Endothelial Function in Obstructive Sleep Apnea. Vanderbilt University is listed as the sponsor. The recorded study start is 2008-02, and primary completion is 2012-04.

The study summary describes research involving health volunteers and patients with newly diagnosed or untreated obstructive sleep apnea. It says the research examines blood clotting factors and blood vessel function to better understand mechanisms associated with cardiovascular risk. The listed groups are Healthy Controls and Obstructive Sleep Apnea Group. Both arm descriptions specify age 18 years or older and body mass index between 25 and 45.

This is not a randomized comparison according to the registry record: allocation is not stated, and the record cautions that the arms are not a like-for-like control comparison. The posted information therefore supports describing a group comparison, not a randomized treatment effect. It does not report how participants were recruited, how obstructive sleep apnea was diagnosed, how control status was established, or whether additional eligibility criteria were applied.

Enrollment is listed as 34. The record identifies 2 outcome measures, including the primary comparison of mean PAI-1 activity and a secondary comparison of endothelial wall diameter. It lists 0 analyses. The outcome description places the primary measurement at the initial visit; further details on measurement procedures, follow-up, and analysis methods are not reported in the registry record.

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: Once patients were enrolled in the trial and assigned to the groups, we were able to complete the protocols without having to exclude any participants.

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 Comparison of Levels of Mean PAI-1 Activity in Patients With Obstructive Sleep Apnea and Controls., measured over at the initial visit.

The primary endpoint is the comparison of mean PAI-1 activity in patients with obstructive sleep apnea and controls. The registry specifies IU/ml as the unit, the mean as the summary measure, and standard error as the dispersion measure. The measurement timeframe is the initial visit.

PAI-1 is identified in the endpoint as an activity measure, and the study summary places blood clotting factors among the biological features under investigation. In general, comparing a continuous measurement between groups can describe whether the observed group averages differ and by how much. The mean gives a summary of the measured values, while the standard error describes the precision of the estimated mean; it is not a description of the spread of individual values.

The registry record does not explain why PAI-1 activity was selected as the primary endpoint, define its clinical interpretation, or report assay details. It also does not provide the observed group means, standard errors, a between-group estimate, a confidence interval, or a p-value. Without those results, the actual endpoint comparison and its precision cannot be evaluated. The listed secondary outcome concerns endothelial blood vessel wall diameter in patients with obstructive sleep apnea versus controls, but its results are likewise not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary endpoint is a continuous measurement summarized by a mean. In general, a mean combines measured values into a group-level average. It is useful for describing the central level of a continuous outcome, but it does not reveal the full distribution of individual observations. Different distributions can have the same mean, so a mean alone does not show whether values cluster closely or vary widely.

The endpoint specifies standard error as the dispersion accompanying the mean. In general, a standard error describes the precision of an estimated mean: smaller standard errors indicate more precise estimates under the assumptions of the analysis. A standard error is not the same as the standard deviation, which describes the spread of observations. The registry record does not report the standard errors or standard deviations for this endpoint, so neither precision nor the variability of individual PAI-1 activity measurements can be assessed from the posted results.

A comparison between group means is usually most informative when it includes an estimate of the difference and an interval expressing uncertainty. In general, a confidence interval gives a range of values compatible with the data and the statistical model at its stated confidence level. A narrow interval indicates greater precision than a wide interval, while an interval spanning values on both sides of no difference may leave the direction uncertain. These are general principles; the registry record does not report a confidence interval or specify an interval method for this comparison.

A p-value, when reported, describes how unusual the data would be under a specified null model and its assumptions. It is not the probability that the null hypothesis is true, nor does it measure the size or importance of a difference. The registry record does not report a p-value for the primary endpoint. The absence of a posted p-value cannot be interpreted as evidence for either a difference or no difference.

The record describes two groups, but this is not a randomized comparison. Allocation is not stated, and the registry explicitly cautions that the arms are not a like-for-like control comparison. In general, random assignment can help balance measured and unmeasured characteristics on average. Without randomization, observed group differences may be associated with the condition, with other participant characteristics, or with both. Statistical adjustment can sometimes address measured differences, but the registry record does not report whether adjustment, matching, or another approach was used.

The record includes a planning illustration framework based on an observed effect. It states assumptions of a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation; the effect to detect is described as a stated fraction of the observed effect. These are planning assumptions, not evidence about the study's original design. No calculated planning sample sizes or observed endpoint effect are reported in the registry record. Such planning values, when available, would be illustrations rather than observed power; they would not establish that the study was adequately powered or that its result is reliable.

In general, over-dispersion means that variability in the data is greater than a model assumes. If a model understates variability, its uncertainty estimates can be too small and inferential conclusions too confident. Whether over-dispersion is relevant depends on the outcome and model. The posted record describes a continuous mean endpoint but does not identify a model or report a check for over-dispersion, so this issue cannot be evaluated for the study.

The endpoint is timed at the initial visit. That defines the stated measurement occasion, but does not reveal details about the sequence of procedures, repeated measurements, or how multiple measurements were combined. Those details are not reported in the registry record. Likewise, the record does not specify how standard errors were estimated or whether the analysis accounted for any design features.

The registry lists 0 analyses and does not provide a numerical primary comparison. Thus, no recalculated unadjusted estimate from posted summary statistics is available to interpret. The sponsor's analysis cannot be compared with an independent recalculation because the registry record does not report either a sponsor result or the summary statistics needed to recalculate one. The appropriate statistical reading is therefore limited to the endpoint definition and the stated design caveats, not an inference about the size or significance of an effect.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Healthy Controls", "Obstructive Sleep Apnea Group")
n   <- c(17, 17)
m   <- c(17.2, 23.9)
sp  <- c(5.3, 5.1)
sd  <- sp * sqrt(n)      # standard errors converted to SDs
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Healthy Controls  17  17.200  21.852  5.965  28.435
CARM  Obstructive Sleep Apnea Group  17  23.900  21.028  13.088  34.712

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 2 outcome measures: the primary comparison of mean PAI-1 activity and a secondary comparison of endothelial wall diameter. It does not report a multiplicity strategy, such as a hierarchy of testing, adjustment of significance thresholds, or designation of outcomes for confirmatory versus exploratory interpretation. When several outcomes are assessed, general statistical practice recognizes that the chance of at least one apparently notable result can increase if each is tested separately. Without a stated plan, the intended interpretation of multiple tests is unclear.

The registry lists 0 analyses and does not post numerical results for either outcome. It does not report whether additional outcomes or subgroup analyses were performed, how many statistical tests were considered, or whether interim analyses were planned or conducted. Those details are not reported in the registry record. No assumption about them is warranted.

Missing-data handling is also not described. The record does not report whether all enrolled participants contributed an endpoint value, whether any measurements were missing, how missing values were handled, or whether sensitivity analyses were conducted. The number enrolled and the safety risk counts do not establish the completeness of the primary endpoint data.

The analysis population is not specified. The registry record does not say whether the primary comparison used all enrolled participants, only participants with available measurements, or another defined population. It also does not give exclusions from the endpoint analysis. Consequently, the relationship between enrollment and the analysis set cannot be assessed.

These reporting gaps matter because multiplicity, missing observations, and analysis-population choices can affect both estimates and uncertainty. Their absence from the registry record is not evidence that a particular method was or was not used; it means the method cannot be evaluated from the posted information.

12. 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.

The registry safety listing reports serious adverse events for Healthy Controls and the Obstructive Sleep Apnea Group. For each group, 17 participants are listed as at risk and 0 as affected by serious adverse events. The listing also reports 17 at risk and 0 affected for other adverse events in each group. Death counts are recorded as null, which means deaths are not reported in the registry record; null should not be read as a reported count of zero.

These entries describe the safety fields posted in the registry, not a complete account of all possible harms. The record does not give event descriptions, severity details beyond the serious-event category, assessment procedures, observation duration, or an explanation of whether all participants were monitored for the same period. It also does not provide a narrative safety report.

A zero affected count in a registry listing means that no affected participants are recorded in that field. In general, it does not prove that an event is impossible or that the study could exclude uncommon harms. Here, the listed counts should be interpreted as registry entries, alongside the missing death counts and lack of further safety detail. They do not provide a basis for broader claims about safety.

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

The study addresses a biological comparison: mean PAI-1 activity in patients with obstructive sleep apnea versus controls, measured at the initial visit. Its stated context is research into blood clotting factors and blood vessel function. The registry also identifies endothelial wall diameter as a secondary outcome. These details show what the study set out to examine.

The posted results do not include the primary endpoint values or a statistical comparison. Therefore, they do not establish whether mean PAI-1 activity differed between groups, the direction of any observed difference, or its precision. The same limitation applies to the secondary outcome, whose results are not reported in the registry record. It is not possible to characterize a null or non-null finding from the available result entries.

The design also limits what a group comparison can establish. Allocation is not stated, and the registry record warns that the arms are not a like-for-like control comparison. In general, an observed difference in a nonrandomized comparison cannot by itself show that obstructive sleep apnea caused the difference. Other characteristics of participants may contribute, and the record does not describe adjustment methods that could clarify this issue.

The study summary discusses cardiovascular risk as motivation, but the listed endpoints are PAI-1 activity and endothelial wall diameter. The record does not report cardiovascular events or evidence that either endpoint predicts or changes clinical outcomes in these participants. A biological measurement is not interchangeable with a clinical outcome.

The safety entries record zero affected participants for serious and other adverse events in both groups, while death counts are not reported in the registry record. These entries should not be expanded into a general statement that no harms occurred or that safety was established. The available information supports a cautious description of the study's question and reporting limitations, not a treatment recommendation or a claim about clinical benefit or harm.

14. Why This Trial Matters Statistically

This study is statistically notable as a comparison of a continuous biological measure across a disease group and healthy controls. Its primary endpoint is defined as mean PAI-1 activity in IU/ml at the initial visit, with standard error named as the dispersion measure. Such detail is useful because it clarifies the type of quantity the study intended to compare, even though the result itself is not posted.

The record also illustrates why design information is essential to interpreting group differences. It does not state allocation and specifically warns that the arms are not a like-for-like control comparison. Group contrasts can be informative descriptions, but without comparable groups or documented adjustment they do not isolate the condition's contribution. That distinction is central when biological markers are studied in clinical populations.

Another statistical lesson is the difference between a question and an answer. A clearly named primary outcome does not reveal the observed effect. To assess evidence, readers need a result estimate and information about uncertainty, along with a description of the analysis. The registry record lists 0 analyses and does not post the group means, standard errors, or inferential result, so the comparison cannot be judged for magnitude or precision.

The record identifies a secondary outcome as well, but does not report how multiple outcomes were handled. In general, knowing which endpoint is primary and how other tests relate to it helps readers distinguish confirmatory from exploratory evidence. The lack of a reported multiplicity plan leaves that interpretation open.

Finally, the safety listing shows why registry fields require careful reading: a zero affected count is distinct from an unreported value, and the death fields are not reported. Together, these features make the study a useful example of the limits of interpreting a registry record when methods and outcome estimates are incomplete.

15. 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 main limitation for statistical interpretation is that the registry record does not report numerical results for the primary endpoint. It names the mean PAI-1 activity comparison and its unit, but provides no group means, standard errors, effect estimate, confidence interval, or p-value. The secondary outcome, endothelial wall diameter, is also listed without a numerical result.

The design description leaves important comparability questions unresolved. Allocation is not stated, and the record cautions that the arms are not a like-for-like control comparison. Both arm descriptions specify age 18 years or older and body mass index between 25 and 45, but those criteria do not establish balance in other characteristics. The record does not report matching, covariate adjustment, or other methods for addressing group differences.

Further methodological details are not reported in the registry record, including how obstructive sleep apnea and control status were determined, how the endpoint was measured, how standard errors were calculated, and which participants were included in each analysis. The handling of missing data and any sensitivity analyses are also not described. The record lists 0 analyses, limiting evaluation of the statistical methods and their implementation.

The registry lists 2 outcomes but does not describe a multiplicity plan, whether additional analyses were conducted, or whether interim analyses took place. The planning illustration assumptions do not supply an observed effect estimate or establish the original design rationale; no calculated planning values are reported. Finally, the safety listing gives death counts as null and does not explain observation duration or monitoring procedures. These omissions constrain interpretation of both efficacy-related outcomes and safety reporting.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Study to Assess the Changes in Blood Clotting Factors and Blood Vessel Wall Function in Obstructive Sleep Apnea — NCT00936481.
• Registry record last updated 2013-10-25; status last verified 2013-08.
• Results first posted 2013-10-25.
• 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.

19. Record Summary

The registry record describes a completed study sponsored by Vanderbilt University, with a recorded start of 2008-02 and primary completion of 2012-04. Enrollment is listed as 34. The study concerns obstructive sleep apnea and describes research involving health volunteers and patients with newly diagnosed or untreated obstructive sleep apnea.

The primary outcome is a comparison of mean PAI-1 activity in patients with obstructive sleep apnea and controls at the initial visit, reported in IU/ml with standard error as the dispersion measure. A secondary outcome compares endothelial wall diameter. The record lists 2 outcome measures and 0 analyses, but does not report numerical outcome results.

Allocation is not stated, and the registry cautions that the arms are not a like-for-like control comparison. Safety listings record 0 serious and 0 other adverse events affecting participants in each group; deaths are not reported in the registry record. The missing endpoint results and methodological details prevent assessment of the size, precision, or statistical significance of the primary comparison.