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 Nasal Pillows vs. Nasal Masks at High CPAP Pressure (NCT01690923), a randomized na study. The primary outcome is AHI on Nasal Mask and Pillows Mask.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01690923 |
| Phase | NA |
| Condition | OSA |
| Allocation | Randomized |
| Design model | Crossover |
| Masking | None (open label) |
| Enrollment | 20 |
| Arms in the primary outcome | n/a |
| Lead sponsor | ResMed |
| Results posted | Yes |
2. Clinical Question
Population
The registry describes participants as current CPAP users with obstructive sleep apnea (OSA). Enrollment was 20. Further eligibility criteria, participant characteristics, and the pressure levels used are not reported in the registry record.
Intervention
The intervention was a pillows mask, identified in the registry as Swift FX. Participants in one sequence used the pillows mask after a nasal-mask period; the other sequence began with the pillows mask.
Comparator
The comparator was a nasal mask. The registry lists Mirage Activa, Micro, and FX models in one sequence description; the other sequence description spells the first model as MMirage Activa. Each mask type was assigned a seven-night period.
Primary question
The primary question was whether AHI during use of nasal pillows was comparable to AHI during use of a nasal mask at high CPAP pressure. The registry also names patient mask-type preference as an aim and usability as a secondary outcome. Numerical AHI results, a comparison estimate, and preference results are not reported in the registry record, so the question cannot be answered from its posted results.
The question concerns a comparison within a crossover evaluation: participants were assigned to a sequence in which they used both mask types, rather than remaining with just one type throughout. This design can make within-participant comparisons possible, because measurements from the same participant may be related. That potential advantage does not establish that the registry used a paired statistical analysis. The analysis method, the sequence allocation counts, and any handling of order or period effects are not reported in the registry record.
The word comparable describes the aim, but the registry does not state a numerical boundary for deciding that the AHI outcomes are sufficiently similar. It also does not report a confidence interval or other result that would show the range of differences compatible with the observed data. Without the outcome results and a stated comparison criterion, the registry record does not establish whether the primary question was resolved.
3. Trial Design
This was a randomized, unmasked crossover study with enrollment of 20. The registry labels the allocation as randomized, masking as none, and model as crossover. The record gives two treatment sequences: nasal mask followed by pillows mask, and pillows mask followed by nasal mask. Each mask type was used for seven nights in the sequence descriptions. The record does not report how many participants were assigned to each sequence or whether all enrolled participants completed both periods.
The nasal-mask period used models identified as Mirage Activa, Micro, and FX in one sequence description. In the other description, the first model is written as MMirage Activa, followed by Micro and FX. The pillows mask is identified as Swift FX. These details identify the devices listed in the registry, but do not give further information about fitting, pressure settings, adherence, or how device use was monitored.
In a crossover design, participants receive more than one condition in sequence. As a general statistical concept, measurements from the same participant may be correlated, and an analysis can account for that pairing. Results may also depend on the order or period of use. The registry does not report a washout period, a method for assessing period or carryover effects, or the statistical model used. Randomization of sequence can help balance order-related influences in expectation, but does not itself explain how those influences were assessed in this evaluation.
The stated aim was to assess comparability of AHI outcomes and patient mask-type preferences at high pressures. Usability is listed as a secondary outcome. The primary outcome timeframe is seven days, and the primary measure is described as average AHI in events/hour for each mask type. The study is marked completed. Its start date is 2011-08 and its primary completion date is 2012-12. Outcome results and analysis details 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.
Overall Study
| Stage | Nasal Mask First, Then Pillows Mask | Pillows Mask First, Then Nasal Mask |
|---|---|---|
| STARTED | 10 | 11 |
| COMPLETED | 10 | 10 |
| NOT COMPLETED | 0 | 1 |
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 | Current CPAP Users |
|---|---|---|
| Participants analysed | 20 | |
| Age, Categorical: <=18 years | Participants | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 8 |
| Age, Categorical: >=65 years | Participants | 12 |
| Age, Continuous | years | 64.6 (SD 9.5) |
| Sex: Female, Male: Female | Participants | 5 |
| Sex: Female, Male: Male | Participants | 15 |
| Region of Enrollment: Australia | participants | 20 |
6. Primary Endpoint
The registry lists the primary outcome as AHI on Nasal Mask and Pillows Mask, measured over 7 days.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Standard Deviation |
| Unit | events/hour |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is AHI on the nasal mask and pillows mask. AHI, or the apnea-hypopnea index, is described in the registry as a measure of sleep-disordered breathing severity. It is recorded as an average number of events per hour, with a seven-day timeframe for each mask type. The endpoint is continuous, and the registry identifies the summary measure as a mean with standard deviation.
As a general explanation, a continuous measure retains information about the size of observed values rather than reducing each participant to a yes-or-no category. A mean describes the central level of values, while a standard deviation describes their spread around the mean. In a crossover comparison, the relationship between each participant’s measurements under the two mask conditions can also matter; group means alone do not reveal that relationship.
AHI is used in this evaluation because the stated primary aim concerns comparable sleep-disordered breathing outcomes with the two mask types under high-pressure CPAP use. The registry record does not specify how AHI was measured or aggregated within each seven-day period, nor does it state a threshold for comparability. It does not report the means, standard deviations, participant-level paired differences, confidence intervals, or a statistical test. Therefore, the endpoint’s definition is available, but the posted record does not show the observed AHI outcomes or their precision.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry identifies AHI as the primary outcome and describes a comparison of nasal-mask and pillows-mask use. It does not report numerical AHI results or an analysis comparing the conditions. The number of analyses recorded is zero, and the registry notes that the primary outcome has fewer than two arms. Consequently, no estimate of the difference between mask types, confidence interval, or test result is available in the registry record. The data posted there cannot establish whether AHI was similar, different, or too imprecisely measured to distinguish between those possibilities.
The distinction between an outcome definition and an outcome result is important. The record states what was intended to be measured, the unit, the summary measure, and the timeframe. Those details do not tell readers what values participants had or how the values differed between the mask periods. Without the numerical results, the magnitude and direction of any observed contrast are unknown. No recalculated comparison can be made from the posted summary statistics because the relevant summary statistics are absent.
The study is described as randomized and crossover. In general, this design can support within-participant comparisons, but interpretation depends on the analysis accounting appropriately for the pairing and on the handling of sequence and period. The analysis population, model, and methods for addressing order or carryover are not reported in the registry record. It is therefore not possible to determine whether the analysis, if one was conducted outside the registry, incorporated these design features.
The stated aim uses the idea of comparable outcomes. As a general statistical principle, a failure to detect a difference is not, by itself, evidence that two conditions are equivalent or sufficiently similar. A formal comparability or equivalence conclusion ordinarily requires a prespecified acceptable margin and an estimate precise enough to assess that margin. Neither a margin nor an inferential result is reported in the registry record. The registry’s aim alone cannot be treated as proof of comparability.
Usability is listed as a secondary outcome, and patient preference is included in the stated evaluation aim. Their numerical findings and measurement details are not reported in the registry record. The safety record lists zero serious events and zero other events among 20 participants at risk in the Current CPAP Users group. These figures describe the registry’s posted safety counts; they do not supply an AHI comparison or preference result.
Any sample-size illustrations associated with the posted material should be interpreted as planning calculations, not as observed trial findings or observed power. The stated illustration assumptions use a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect to detect expressed as a fraction of the observed effect. The registry does not report the trial’s own sample-size justification or establish that these assumptions were the trial’s design assumptions. In particular, a two-arm illustration does not by itself describe the analysis of a crossover study.
9. Statistical Methods Explained
What does a crossover design imply?
The registry identifies this evaluation as a randomized crossover study. Participants were assigned to one of two orders: nasal mask followed by pillows mask, or pillows mask followed by nasal mask. Each mask period was described as seven nights. Unlike a parallel-group design, in which each participant uses only one assigned condition, a crossover design exposes participants to both conditions in sequence. This makes it possible in principle to compare each participant with their own measurements under the other condition.
As a general statistical explanation, a paired analysis uses the relationship between measurements from the same participant. If observations within a participant are correlated, treating them as if they came from unrelated participants may fail to reflect the design. The registry does not report the analysis model, whether a paired comparison was used, or how repeated measurements within a period were summarized. The design label alone does not identify the method used for analysis.
Order and period can also matter. Measurements during a later period could be influenced by time, sequence, or experience with the earlier condition. A washout period, if any, and methods for examining period or carryover effects are not reported in the registry record. Random assignment to sequence is a design feature, but it does not reveal whether or how those issues were evaluated in the analysis.
What does the endpoint summary mean?
The primary outcome is a continuous measure: average AHI in events/hour for nasal-mask and pillows-mask use, with a seven-day timeframe. The registry identifies the summary as mean and standard deviation. As a general explanation, a mean describes the average level of a measure, while a standard deviation gives information about variation among the values. Neither alone gives the uncertainty around a comparison between conditions. A confidence interval for a contrast would describe a range of values compatible with the observed data under the analysis assumptions.
For a crossover comparison, the distribution of within-participant differences can be important. Separate means and standard deviations for each mask do not necessarily reveal the variability of those differences, because that variability depends partly on how measurements from the same participants relate to each other. The registry does not post those summaries, a contrast estimate, or a confidence interval. No interpretation of the size or precision of an AHI comparison can therefore be made from the record.
What is the role of randomization and masking?
The allocation is recorded as randomized, and masking is recorded as none. As a general concept, randomization of sequence can reduce systematic differences between sequence groups in expectation. It does not ensure that all potential differences are balanced in a small study, and it does not remove the need for an analysis suited to the crossover structure. The registry does not report the randomization procedure or sequence counts.
With no masking, participants and relevant study personnel may have known which device was in use. This is a design characteristic, not proof that measurements were biased. Its possible relevance depends on how outcomes were collected. The registry does not describe the AHI measurement process, participant-reported preference instrument, or steps taken to reduce measurement or reporting influences.
What can be learned from the planning assumptions?
The posted planning illustration is described as a calculation based on an observed effect, not as the trial’s own design justification. It assumes a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is expressed as a stated fraction of the observed effect. Time-to-event illustrations are described as total event counts, while other illustrations are described as participants per arm.
As a general explanation, a planning calculation estimates the sample size that would be needed under chosen assumptions to target a specified probability of detecting an effect at a chosen significance level. It is not an analysis of the trial’s observed outcomes. A calculation based on the observed effect is especially dependent on that effect estimate and its uncertainty. It should not be read as observed power, nor does it establish that the study was designed using those assumptions. The actual sample-size justification is not reported in the registry record.
The stated equal-allocation, two-arm assumptions also do not describe all features of a crossover comparison. Participants used both mask types, and sequence rather than a single permanent treatment assignment is described. A sample-size method for a crossover design may depend on within-participant variability and correlation, among other assumptions. Those design inputs and any trial-specific calculation are not reported in the registry record. No sample-size conclusion about the adequacy of the enrolled 20 participants can be drawn from the design label alone.
Why does over-dispersion matter in general?
Over-dispersion is a general statistical issue that arises when the variability in observed data exceeds what a chosen model assumes. When present and ignored, standard errors can be too small, making confidence intervals appear narrower and tests appear more decisive than warranted. Whether this issue applies depends on the outcome and analysis model. The registry does not report an analysis model or diagnostic assessment, so over-dispersion cannot be evaluated for this study’s primary endpoint.
The same general principle applies more broadly: a statistical method needs assumptions suited to the outcome distribution, study design, and dependence between measurements. The registry record gives the primary outcome’s measure and summary type but does not report the inferential method, model checks, or adjustments. Describing general methods does not establish which methods were actually used.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists two outcome measures and identifies AHI as the primary outcome. Usability is listed as a secondary outcome, while patient mask-type preference is part of the stated aim. The number of analyses recorded is zero, and no numerical outcome analyses are reported. A procedure for controlling multiplicity across outcomes, comparisons, or analyses is not reported in the registry record.
As a general statistical explanation, multiplicity arises when several hypotheses or outcomes are examined. Without a prespecified strategy, the chance of at least one apparently unusual result can increase as more comparisons are considered. That general concern does not show that any particular result is false, and there are no posted outcome tests to evaluate in this record. The analysis plan and any multiplicity adjustment are not reported.
The registry does not report the number of participants with usable primary-outcome data, exclusions from analysis, or the analysis population. Completion of the study is recorded, but completion status does not establish that every participant contributed data to every outcome or period. Missing-data amounts, reasons, handling methods, and sensitivity analyses are not reported in the registry record.
For a crossover study, missing measurements in one period can affect whether a participant contributes a complete within-participant comparison. As a general concept, the consequences depend on the amount and pattern of missingness and on the analysis method. The registry does not provide enough information to assess these features. It also does not report whether the primary analysis followed an intention-to-treat, per-protocol, or another population definition.
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 |
|---|---|---|---|
| Current CPAP Users | 0 | 20 | 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 |
|---|---|
| Current CPAP Users | 0 of 20 |
The registry lists a safety group titled Current CPAP Users, with 20 participants at risk for serious adverse events and zero affected. It also lists 20 participants at risk for other adverse events and zero affected. No serious adverse-event terms are listed. Deaths are recorded as null, which is not the same as a reported count of zero.
These are the posted registry counts. The denominators identify the number recorded as at risk in this safety group; they do not show how events were distributed by mask type or treatment period. The record does not explain event-collection procedures, surveillance duration, or whether the safety counts correspond to exposure to each mask separately. It also does not provide event-level descriptions beyond the absence of listed serious-event terms.
As a general statistical point, observing zero events in a study does not establish that an event is impossible or that a device has no risk. The precision of a safety estimate depends on the amount and duration of observation and on how events were ascertained. Those details are not reported in the registry record. The posted figures should therefore be read as counts for this recorded group, not as a complete estimate of comparative safety between the masks.
12. What the Result Does, and Does Not, Mean
The registry record establishes that a randomized, unmasked crossover evaluation was conducted in 20 participants, comparing nasal masks and pillows masks across sequential seven-night periods. It identifies AHI as the primary outcome and usability as a secondary outcome. It also states that patient mask-type preference was an aim. These details describe the research question and design, not the observed clinical outcomes.
No numerical AHI values or comparison analysis are reported. As a result, the record does not show the direction or size of an AHI contrast, how uncertain any contrast was, or whether the data met a criterion for comparability. The word comparable in the study aim should not be mistaken for a finding. The registry does not report a comparability margin, and it does not post the results needed to assess one.
Preference and usability findings are also not reported. The safety record lists zero serious adverse events and zero other adverse events among the 20 people at risk in the Current CPAP Users group, while the deaths field is null. These counts are limited to what the registry records; they do not establish comparative safety by mask or period.
As a general statistical principle, a study’s design and sample size do not substitute for outcome estimates. A crossover design can allow within-person comparison, but meaningful interpretation still depends on the actual data, the analysis, and its assumptions. Those outcome and analysis details are not reported in the registry record. The appropriate conclusion is therefore limited: the registry describes an evaluation intended to compare mask types, but its posted results do not answer whether the primary AHI outcomes were comparable.
13. Why This Trial Matters Statistically
This trial matters statistically because it poses a within-participant comparison. When the same participant uses each mask type, comparisons can account for stable individual characteristics that might differ between separate groups. This is a potential feature of the crossover design, not evidence that the analysis used the pairing correctly or that it produced a precise comparison.
The design also makes period and sequence relevant. Measurements could vary with order or time, and the way these factors are handled can affect interpretation. The registry identifies the randomized sequences and period lengths, but does not report a washout, analysis model, or assessment of period and carryover effects. Readers can see the structure intended for the comparison but cannot evaluate how it was incorporated into the analysis.
The record illustrates another important statistical distinction: naming a primary endpoint is not the same as reporting an endpoint result. AHI is defined as a continuous measure summarized by mean and standard deviation, yet no values, contrasts, or uncertainty measures are posted. Consequently, no inference about the relative AHI outcomes can be made. The stated aim of comparability also highlights why a decision criterion matters; without a reported margin and estimate, similarity cannot be assessed from the record.
Finally, the study’s completed status and the safety counts do not fill the gaps in the efficacy results. The registry reports no primary outcome analyses, and the preference and usability findings are absent. Statistical interpretation depends on estimates, uncertainty, and methods, not only on the trial’s question or design. This record is useful for understanding what was planned and how participants were assigned, but it does not support a quantitative conclusion about the primary comparison.
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.
A central limitation of the registry record is that it does not report numerical results for the primary AHI outcome. It also does not report a comparison estimate, confidence interval, or test. The number of analyses recorded is zero, and the record notes fewer than two arms in the primary outcome. Without those results, the intended comparison cannot be evaluated statistically.
The registered sample was 20, but the record does not provide the number assigned to each sequence, the number completing both periods, or the analysis population. It does not report missingness by outcome or period, reasons for missing observations, or how missing data were handled. The actual sample-size justification is not reported in the registry record.
Important details for interpreting a crossover comparison are also absent. The registry does not report a washout period, methods for assessing period or carryover effects, the model used for analysis, or whether the analysis accounted for within-participant correlation. The pressure levels and the operational definition of high pressure are not reported. The measurement process for AHI is not described in enough detail to assess how values were collected and summarized during each period.
Masking is recorded as none. This does not establish that the outcomes were biased, but the registry does not describe procedures that would clarify how knowledge of the device may have influenced outcome measurement or reporting. Preference and usability measurement details and results are not reported. The registry also contains a spelling difference in the nasal-mask model description across sequence entries: one lists Mirage Activa and the other lists MMirage Activa. These limitations restrict interpretation of the registered information; they do not establish what may have been documented outside the registry record.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Nasal Pillows vs. Nasal Masks at High CPAP Pressure — NCT01690923.
- Registry record last updated 2014-10-08; status last verified 2014-09.
- Results first posted 2014-10-08.
- 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.
Continue through the Clinical Biostats statistical pathway
Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
18. Record Summary
The registry record describes a completed randomized, unmasked crossover evaluation sponsored by ResMed, with enrollment of 20 and OSA listed as the condition. The study began in 2011-08 and has a primary completion date of 2012-12. Participants were assigned to one of two sequences using nasal masks and pillows masks, with seven nights described for each mask period.
The primary outcome was AHI on nasal mask and pillows mask, measured as average events/hour over a seven-day timeframe and summarized as a mean with standard deviation. Usability is listed as a secondary outcome, and patient mask-type preference is included in the stated aim. Numerical primary outcome results, preference findings, usability results, and analysis methods are not reported in the registry record. The safety listing records zero serious and zero other adverse events among 20 at risk in the Current CPAP Users group; deaths are recorded as null.