Effects of CPAP on Diet, Physical Activity, and Cardiovascular Risk: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Effects of CPAP on Diet, Physical Activity, and Cardiovascular Risk (NCT01944020), a non-randomized na study. The primary outcome is Fat Mass (% of Total Body Mass).

2. Clinical Question

The study concerns whether CPAP use is associated with changes in body composition in people with obstructive sleep apnea. Its rationale describes possible links among sleep apnea, energy balance, physical activity, appetite-regulating hormones, and weight gain. Those proposed links motivate the research question; they are not findings established by the registry record.

The primary measure was recorded at baseline and after the two-month treatment or control period. The registry also identifies ad libitum food intake, measured as total daily calories consumed, as a secondary outcome. The summary describes an investigation of energy balance and cardiovascular risk, but the numerical results for these outcomes are not reported in the registry record.

Because allocation was nonrandomized, the groups should not be treated as a like-for-like controlled comparison. Differences between them could reflect factors other than CPAP use. The record therefore supports describing the study question and its measured outcomes, but it does not establish a causal treatment effect. In addition, without posted primary outcome values or a reported analysis, the direction, size, and precision of any observed change cannot be assessed.

3. Trial Design

This was a completed, parallel-group study with nonrandomized allocation and no masking. The registry lists an enrollment of 29. It identifies Columbia University as the sponsor, a start date of 2015-05, and a primary completion date of 2018-09. The phase is recorded as NA.

The intervention group used active CPAP at a therapeutic dose each night for two months. The control group did not use CPAP for two months. The study summary says patients were instructed to use CPAP at home nightly during the treatment phases. Fat mass was measured at baseline and at the end of the treatment or control period. The primary outcome description specifies measurement by BODPOD and refers to participants who completed the CPAP and non-CPAP groups.

Nonrandomized allocation means that assignment was not made by chance, according to the registry. The record does not describe how participants entered or were assigned to the groups, so the possibility of systematic differences between groups cannot be evaluated from the recorded details. Such differences can complicate interpretation: for example, a change over time in one group does not by itself show that CPAP caused that change, and a contrast between groups may also reflect baseline or other differences.

The study is described as parallel rather than as a crossover design. Its outcome timeframe is baseline and the end of the two-month treatment or control period. Further details about visit scheduling, adherence assessment, protocol deviations, or the timing of other measurements are not reported in the registry record. Although the study status is completed, completion status alone does not supply the numerical results or the analysis needed to evaluate the primary question.

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

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: all completed CPAP group and non-CPAP group participants

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.

Population: Participants who completed the intervention

6. Primary Endpoint

The registry lists the primary outcome as Fat Mass (% of Total Body Mass), measured over At baseline ("Pre") and after 2 months of treatment ("Post") or control.

The primary endpoint is fat mass expressed as a percentage of total body mass. The registry describes this as a mean with standard deviation and states that it was measured by BODPOD at baseline and at the end of the treatment or control period. The stated population is participants who completed the CPAP group and the non-CPAP group.

As a measure of body composition, a percentage expresses fat mass relative to total body mass rather than as an absolute amount. This can be useful when the research question concerns the composition of body mass. Generally, however, a percentage should be interpreted in relation to its denominator: a change in the percentage can reflect changes in fat mass, total body mass, or both. It is not interchangeable with a direct measure of cardiovascular risk or with body weight alone.

The baseline and end-of-period measurements allow investigators to describe how the endpoint changed over the study period. A comparison between groups could provide additional context, but its interpretation depends on the analysis and on how comparable the nonrandomized groups were. The registry does not report the numerical means, standard deviations, changes, or between-group contrast. It also does not report a confidence interval or test result for this endpoint. Consequently, the endpoint's observed direction, magnitude, and statistical precision are not available in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a mean with a standard deviation describe?

The primary endpoint is specified as a mean with a standard deviation. Generally, the mean describes the central value of a continuous measurement across the observations included in an analysis. The standard deviation describes how spread out individual measurements are around that mean. It is not the same as a confidence interval: a standard deviation describes variability among observations, while a confidence interval describes uncertainty around an estimated quantity.

The registry record does not report the endpoint means or standard deviations. It also does not say whether the principal comparison was based on end-of-period values, changes from baseline, or another formulation. Those choices can answer related but distinct questions, particularly when baseline values differ between nonrandomized groups.

How should baseline and follow-up measurements be understood?

Fat mass percentage was measured at baseline and after the two-month treatment or control period. Generally, repeated measurements on the same participant are related rather than independent. An analysis of change can account for that relationship, while an analysis that treats measurements as unrelated may use the available information differently. Which approach was used is not reported in the registry record.

A change within the CPAP group would describe change among its measured participants over time. A change within the no-CPAP group would describe change among its measured participants over time. To estimate a contrast between the strategies, an analysis would need to compare the groups in a way consistent with the study question. Because the groups were not randomized, measured and unmeasured differences may affect that contrast. The record does not report an adjustment method or identify covariates used in an analysis.

What would a confidence interval contribute?

Generally, a confidence interval gives a range of values compatible with an estimate under the assumptions of the statistical method. Its width conveys information about precision: a narrower interval indicates greater precision than a wider interval, all else equal. The interval does not remove bias from confounding, measurement, or selection. In a nonrandomized study, a precise estimate can still be biased if the comparison is not sufficiently comparable.

No confidence interval for the primary outcome is reported in the registry record. Without an estimate and its interval, readers cannot assess either the apparent size of a difference or the uncertainty around it. A significance test, if available, would not substitute for that information; a test addresses compatibility with a specified null hypothesis under its assumptions, not whether an effect is important or free from bias.

What can be said about planning calculations?

The record describes planning illustrations based on an observed effect. Their stated assumptions are a two-sided significance level of 0.05, equal allocation, and a normal approximation, with the effect to detect set as a stated fraction of the observed effect. For outcomes other than time-to-event outcomes, such illustrations are expressed as participants per arm. These assumptions describe the planning illustration, not the design of the completed trial. The numerical illustrations themselves are not reported in the record details.

Such calculations are not observed power. Generally, planning calculations ask how many participants would be needed under specified assumptions to detect a chosen effect with a chosen probability. An illustration based on an observed effect is especially dependent on that effect estimate, which may be uncertain. It should not be interpreted as proof that the completed study had adequate power or that a result is reliable. The record does not report a trial-specific sample-size justification or its assumptions.

Why can variability matter?

Generally, greater variability in a continuous outcome makes it harder to estimate a group mean or a difference precisely, all else equal. Standard deviations help describe that variability. In some settings, data may show more variability than a simple statistical model expects; this is called over-dispersion. Accounting for over-dispersion can affect uncertainty estimates and tests. The primary endpoint is described with a standard deviation, but the record does not report an over-dispersion assessment or a model for the outcome. There is no basis to say that over-dispersion was present or that a particular method was used to handle it.

What analysis details are absent?

The registry reports 0 analyses and does not provide numerical primary outcome results. A complete statistical interpretation would ordinarily need the analyzed values or estimates, the number of observations contributing to each analysis, the method used to compare groups, handling of baseline values, uncertainty estimates, and any model assumptions. These details are not reported in the registry record. The outcome population is described as participants who completed the CPAP and non-CPAP groups, but the record does not explain how completion was defined or how participants without endpoint measurements were handled.

10. Multiplicity, Missing Data and Analysis Populations

The registry states that there were 3 outcome measures and identifies ad libitum food intake, expressed as total daily calories consumed, as a secondary outcome. The listed primary outcome is fat mass as a percentage of total body mass. The identities and analysis details for all outcome measures are not fully reported in the registry record.

When a study examines multiple outcomes or performs multiple statistical tests, the chance of obtaining at least one apparently unusual result can increase. Generally, a multiplicity strategy specifies which outcomes or comparisons are primary and whether or how significance thresholds or interpretation will account for the number of analyses. The registry record does not report a multiplicity adjustment, a hierarchy among outcomes beyond identifying the primary measure, or a plan for handling multiple comparisons. It is therefore not possible to determine how multiplicity was addressed.

Missing-data handling is also not reported in the registry record. The primary outcome population is described as participants who completed the CPAP and non-CPAP groups, but no definition of completion, missingness summary, imputation method, or sensitivity analysis is stated. Generally, excluding participants without complete measurements can affect a result if missingness is related to participant characteristics or outcomes. The direction or extent of any such effect cannot be assessed without further details.

The record does not report an analysis population such as an intention-to-treat population, nor does it describe how nonadherence, withdrawal, or other deviations were treated. These omissions limit evaluation of the outcome analysis and of how well it represents the participants enrolled in the study.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The registry lists 0 serious adverse events and 0 other adverse events among 12 participants at risk in the CPAP group. It lists 0 serious adverse events and 0 other adverse events among 12 participants at risk in the no-CPAP group. Deaths are recorded as 0 in each group.

These figures should be read as the event counts and at-risk counts entered in the registry, not as a general guarantee that no adverse events occurred. The record does not provide descriptions of event definitions, duration of safety observation, completeness of reporting, or whether participants contributed different amounts of observation time. It also does not explain how the at-risk counts relate to the overall enrollment.

A zero count in a group does not establish that the underlying risk is zero. Generally, observed counts are limited by the number of participants observed, the length and completeness of follow-up, and how events are collected and classified. The posted figures describe the registry's recorded safety data; they do not by themselves establish comparative safety or answer the primary body-composition question.

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

The study asks whether fat mass as a percentage of total body mass changes between baseline and the end of two months of CPAP use or no CPAP use. The registry describes a nonrandomized, parallel-group design and identifies the primary endpoint, but it does not report numerical outcome findings. As a result, the posted record cannot establish whether the measure increased, decreased, or remained similar, nor how large or precise any change was.

Even if numerical changes were available, a change observed during CPAP use would not by itself show that CPAP caused it. Participants were not randomly allocated, and the registry does not report enough about group comparability or adjustment to assess confounding. A comparison with the no-CPAP group could help describe differences over the same period, but nonrandomized allocation remains a limitation for causal interpretation.

The endpoint is a body-composition measure, not a direct measurement of every element named in the study rationale. The record identifies food intake as a secondary outcome, but numerical results for that outcome are not reported. A broad motivation involving energy balance and cardiovascular risk should not be read as evidence of a change in diet, activity, or cardiovascular outcomes.

The safety counts record no serious or other adverse events and no deaths in the listed at-risk groups. Those counts are limited to the registry's recording and do not establish absence of risk. Taken together, the record describes what the study set out to compare and how it characterized its primary endpoint, but it does not provide enough results to determine the observed outcome or its uncertainty.

13. Why This Trial Matters Statistically

This study is statistically informative as an example of the distinction between a defined research question and an evaluable result. The registry identifies a continuous primary endpoint, a baseline and follow-up timeframe, a treatment group, and a no-CPAP comparison. Those details clarify what the investigators intended to measure. However, a measurement definition alone cannot show whether the groups differed or how precisely a difference was estimated.

The nonrandomized allocation also makes design interpretation central. Statistical adjustment can sometimes account for measured differences between groups, but it cannot guarantee control of unmeasured confounding. Since the registry does not report an adjustment strategy or numerical analyses, readers cannot assess whether the comparison addressed potential baseline differences. This is why the design must shape the strength of any causal claim, even if an estimate is eventually available.

The endpoint is reported as a mean with standard deviation, which distinguishes average level from variation among observations. A complete account would also communicate the estimated contrast and its uncertainty. Without those numerical results, there is no basis to judge whether an apparent difference is small or large, precise or imprecise, or compatible with no difference.

The record also illustrates why outcome multiplicity and missing-data methods matter. It names a secondary outcome and reports 3 outcome measures, but it does not describe multiplicity handling or missing-data procedures. These details help readers understand how analyses were selected and which participants contributed to them. Their absence, together with the lack of numerical results, limits independent statistical 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 main limitation for interpreting this trial record is that numerical results for the primary endpoint are not reported in the registry record. Means, standard deviations, estimated changes, between-group contrasts, confidence intervals, and test statistics are unavailable. Without these, the observed direction, magnitude, and precision cannot be evaluated.

Nonrandomized allocation limits causal interpretation. The registry does not describe how participants came to be in the CPAP or no-CPAP group, whether baseline characteristics differed, or whether statistical adjustment was performed. Consequently, the extent to which group differences could reflect factors other than CPAP use is not reported.

The primary outcome population is described as participants who completed the two groups, but the record does not define completion or state how missing measurements were handled. It does not report adherence results, losses to follow-up, or sensitivity analyses. These omissions prevent assessment of how the analyzed population may differ from those enrolled.

The record names one secondary outcome and states that there were 3 outcome measures, while the full outcome analysis details are not reported. Multiplicity methods, model specifications, and the statistical analysis plan are not reported in the registry record. The planning assumptions are described as an illustration based on an observed effect, but no numerical planning values or trial-specific sample-size justification are available in the record details. The serious and other adverse-event counts are also limited by the lack of reported detail about event definitions and safety observation.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Effects of CPAP on Diet, Physical Activity, and Cardiovascular Risk — NCT01944020.
• Registry record last updated 2022-05-03; status last verified 2022-04.
• Results first posted 2022-05-03.
• 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.

18. Record Summary

NCT01944020 is a completed, nonrandomized, unmasked, parallel-group study sponsored by Columbia University. It lists an enrollment of 29 and compares active CPAP use at home each night for two months with no CPAP use for two months. The registry gives a start date of 2015-05 and a primary completion date of 2018-09.

The primary endpoint is mean fat mass as a percentage of total body mass, measured by BODPOD at baseline and after the treatment or control period. The primary outcome population is described as participants who completed the CPAP and non-CPAP groups. Ad libitum food intake, measured as total daily calories consumed, is identified as a secondary outcome.

Numerical outcome results and analysis details are not reported in the registry record. Safety counts list 0 serious adverse events, 0 other adverse events, and 0 deaths in each group, with 12 participants at risk in each group for the adverse-event counts.