GLYCOSA Study:Effect of PAP Treatment on Glycemic Control in Patients With Type 2 Diabetes: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for GLYCOSA Study:Effect of PAP Treatment on Glycemic Control in Patients With Type 2 Diabetes (NCT00509223), a randomized na study. The primary outcome is HbA1c Change.

2. Clinical Question

3. Trial Design

The GLYCOSA study (NCT00509223) is recorded as a randomized, parallel-group trial with no masking. It is marked completed. ResMed is listed as the sponsor. The registry gives a start date of 2007-07 and a primary completion date of 2012-02. The recorded enrollment is 416.

The two arms differed by PAP use. One arm received lifestyle counseling with PAP therapy, and the other received lifestyle counseling without PAP therapy. The registry summary describes a six-month CPAP treatment evaluation and follow-up at 3 months and 6 months, with laboratory assessments intended to evaluate glycemic control. The primary endpoint is specifically defined as change in HbA1c from baseline to Month 6.

Random allocation is intended to create groups that are comparable on average, while the parallel design means participants were assigned to one group rather than crossing between treatments. Because masking is listed as none, participants and study personnel were not masked according to the record. The registry does not report further details about how the random sequence was generated, whether allocation was concealed, or how masking was handled for laboratory measurement.

The primary endpoint results include 129.0 participants in the lifestyle-counseling-with-PAP arm and 138.0 in the lifestyle-counseling arm. These are the arm counts shown for this outcome, whose analysis population required a baseline and at least one follow-up HbA1c value. The record does not report the reasons participants were absent from this analysis or provide a detailed account of retention by visit.

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: Subjects were presented with an Informed Consent Form (and HIPAA in USA) and assessed for eligibility based on inclusion /exclusion criteria. If all IEC met, subjects randomized 1:1. 118 subjects not included in endpoint analysis due to reanalysis of Obstructive Sleep Apnea (OSA) inclusion criteria. 298 of the 416 were included for final analysis.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: The following definition was applied to the primary endpoint: included in analysis were all participants that had at least 1 follow-up HbA1c value in addition to the Baseline HbA1c were considered.

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: 118 subjects (of the 416 that started in the participant flow module) were not included in endpoint analysis due to reanalysis of OSA inclusion criteria. Thus, 298 of the 416 were included for final analysis.

6. Primary Endpoint

The registry lists the primary outcome as HbA1c Change, measured over Baseline to Month 6.

The primary endpoint is change in HbA1c from baseline to Month 6, measured as HbA1c percent. HbA1c is a laboratory measure used to assess glycemic control over time. A change score expresses how the measurement at follow-up differs from the baseline measurement for each participant; the reported arm results summarize those changes with means and standard deviations.

Using change from baseline makes the endpoint directly address the study’s stated objective of assessing glycemic control after treatment. The comparison asks whether average change differed between participants assigned to lifestyle counseling with PAP and those assigned to lifestyle counseling alone. The registry reports a mean change of -0.1 for each group.

The endpoint population was defined as participants with at least one follow-up HbA1c value in addition to the baseline value. This definition identifies who could contribute a change measurement, but it does not explain how missing follow-up measurements were handled or whether other analysis populations were planned. Those details are not reported in the registry record.

HbA1c is one measure of glycemic control, not a complete account of every outcome named in the study objectives. The registry also describes interest in glucose measures, biochemical markers, cardiovascular outcomes, and quality of life, but no secondary results are posted in this record.

7. Results Posted in the Registry

• Lifestyle Counseling: mean -0.10 versus -0.10 on control; difference 0.00 (95% CI -0.18 to 0.18), standardized effect d = 0.00; z-test p = 1.000.

8. Statistical Interpretation

9. Statistical Methods Explained

What does the mean change represent?

For a continuous measure such as HbA1c, a mean summarizes the average value across the observations in a group. Here the outcome is a change from baseline to Month 6, so the arm means describe average change rather than the average Month 6 measurement alone. The registry reports a mean change of -0.1 in each arm. The accompanying standard deviations, 0.8 and 0.7, describe how dispersed the individual changes were around their respective group means.

A standard deviation is not a confidence interval and is not a direct measure of how precisely the difference between groups has been estimated. A group can have substantial variation among individuals while its mean is estimated with greater precision, depending in part on the number of observations. The posted outcome counts are 129.0 for the PAP arm and 138.0 for the counseling arm.

What does the mean difference compare?

The mean difference is a contrast between the groups’ average changes. The reported estimate is 0.0. This estimate is the quantity to interpret as the observed average contrast, not as a percentage of participants or a relative effect. The arm means are rounded, and the reported contrast is also rounded; the displayed values should not be taken to imply identical individual responses or exact equality in the unrounded data.

The record provides a confidence interval for the contrast and an unadjusted p-value of 1.0. The interval indicates a range of estimates compatible with the data under the method used to form it. Its inclusion of zero means that no difference is among the values compatible with the interval. A p-value summarizes compatibility with a null model, but does not give the probability that a treatment effect exists or that the null is true.

Why does the analysis population matter?

The primary endpoint definition includes participants who had a baseline HbA1c and at least one follow-up HbA1c value. A participant without a follow-up value cannot contribute a baseline-to-follow-up change under that definition. Consequently, the posted endpoint analysis is not described as including every randomized participant automatically. The registry reports the arm counts used for this outcome, but does not give the reasons for missing measurements or specify an imputation procedure.

In general, missing outcome data can affect interpretation if the participants with observed follow-up measurements differ systematically from those without them. That is a general concern about incomplete follow-up, not a finding established by this record. The registry does not report sensitivity analyses that would show how alternative assumptions about missing values might affect the result.

What statistical details are not available?

The registry record does not report the statistical test used for the contrast, a model specification, covariate adjustment, the confidence interval’s stated confidence level, or a detailed statistical analysis plan. It also does not report whether the analysis was designated as intention-to-treat or per-protocol. Randomization is recorded, but details such as sequence generation and allocation concealment are not reported in the registry record.

General statistical context can help distinguish these methods without assuming which were used. An unadjusted comparison estimates a contrast without accounting for additional covariates in a model. An adjusted analysis can account for measured variables, but its interpretation depends on the variables and model specified. The posted record does not establish that such an adjusted analysis was performed.

Over-dispersion is a general issue for outcomes whose variability exceeds what a chosen model expects; accounting for it can affect standard errors and inference. This endpoint is continuous and its result is summarized by means and standard deviations. The registry does not report an over-dispersion assessment or model-based variance adjustment, so no such procedure should be attributed to the trial.

The record lists one outcome measure and no posted analyses in its analysis information. It does not report a multiplicity procedure. Therefore, there is no basis in the registry record for claiming that the primary comparison was adjusted for multiple outcomes, repeated looks at the data, or other testing. These missing methodological details limit how specifically the inferential result can be reconstructed from the posted summary statistics.

10. Confidence Intervals and Precision

The reported confidence interval concerns the mean difference in HbA1c change. It includes 0.0 and extends to values on both sides of zero. This means the posted estimate is compatible with no average difference as well as with some difference in either direction. The registry does not report the confidence level attached to this interval, so it should not be labeled with a particular confidence percentage.

In general, a confidence interval communicates both the direction and precision of an estimate under the method used to construct it. An interval concentrated near the null value would indicate greater precision around a small contrast; a wider interval would leave more possible contrasts compatible with the data. The interval reported for this result is not a guarantee that the true effect lies within its limits, and it is not a probability statement about the particular treatment effect.

The estimate is 0.0, but the interval’s inclusion of values other than zero matters: a point estimate alone does not convey the uncertainty in the contrast. Conversely, an interval that includes zero does not demonstrate equivalence. Equivalence requires a prespecified margin defining differences considered acceptably small and an analysis designed to assess that margin. Such a margin and an equivalence analysis are not reported in the registry record.

The displayed means and standard deviations are rounded summaries, and no participant-level data are posted in this record. Thus, readers cannot use these summaries alone to inspect the distribution of change, identify unusual observations, or determine whether the mean adequately represents the pattern of individual outcomes. The reported interval remains the record’s direct summary of uncertainty for the mean difference.

11. Multiplicity, Missing Data and Analysis Populations

The registry describes several secondary objectives, including fasting and post-prandial glucose, biochemical markers, cardiovascular outcomes, and quality of life. However, no secondary results are posted in the record. It lists one outcome measure and no analyses in its analysis information. A plan for controlling multiplicity across multiple outcomes or analyses is not reported in the registry record.

Multiplicity matters when several hypotheses are tested: the chance of at least one apparently notable result can increase as the number of tests increases. That is a general statistical issue, not evidence that such testing occurred in this trial. Because the registry does not report a multiplicity plan or secondary analyses, the primary comparison should be read as the posted result rather than as a fully documented family of tests.

The primary endpoint population includes participants with baseline HbA1c and at least one follow-up HbA1c value. The record reports 129.0 participants in the PAP arm and 138.0 in the counseling arm for the endpoint. It does not report how many randomized participants lacked eligible follow-up measurements, why measurements were missing, or whether missing data were imputed. A sensitivity analysis for missing outcomes is also not reported in the registry record.

The record does not specify an intention-to-treat or per-protocol analysis population, nor does it describe deviations from assigned treatment or adherence-based exclusions. The definition based on observed HbA1c follow-up should therefore be kept distinct from a claim that all randomized participants were analyzed under their assigned groups. A detailed statistical analysis plan, including prespecified handling of missing data and multiplicity, is not reported in the registry record.

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.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: procedure (1.4%), tia / blockage of artery (1.3%), headache (0.7%), pain (0.7%), ovarian cancer (0.7%).

The registry records serious adverse event figures for both arms. For lifestyle counseling, the serious-event count is 5 among 147 at risk. For lifestyle counseling with PAP therapy, it is 10 among 151 at risk. The record also lists other adverse events as 78 among 147 at risk for lifestyle counseling and 94 among 151 at risk for lifestyle counseling with PAP therapy. These are reported counts and denominators, not calculated comparative effects.

The serious-event terms listed include Procedure (1.4%), TIA / Blockage of Artery (1.3%), Headache (0.7%), Pain (0.7%), Ovarian Cancer (0.7%), and GI Distress (0.7%). The registry record does not explain the event-term coding or provide the context needed to attribute an event to a treatment. These figures alone do not establish causation or a comparative safety effect.

Deaths are not reported in the registry record. The safety denominators differ from the posted primary endpoint counts, so the safety figures should not be treated as though they describe the same analysis population. The record does not provide additional details on timing, severity categories beyond serious events, or exposure duration for these counts.

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

The posted result addresses a specific question: how the mean HbA1c change from baseline to Month 6 compared between lifestyle counseling with PAP and lifestyle counseling alone among participants meeting the endpoint’s follow-up definition. The reported means were -0.1 in each arm, the mean difference was 0.0, and the unadjusted p-value was 1.0. The confidence interval includes zero.

These findings do not establish that the groups were equivalent. A failure to demonstrate a difference is not the same as demonstrating that any difference is small enough to be unimportant. Equivalence or non-inferiority requires a prespecified margin and corresponding analysis, neither of which is reported in the registry record. The available interval also leaves room for nonzero contrasts.

The result does not answer whether PAP affected fasting or post-prandial glucose, biochemical markers, cardiovascular outcomes, or quality of life. Although these appear among the study objectives, secondary results are not posted in the registry record. Nor does the primary endpoint by itself describe treatment adherence, changes in other care, or individual variation in response.

The finding should not be translated into a clinical recommendation. No threshold for a clinically meaningful HbA1c change is reported, and the record does not provide the broader evidence needed to make treatment decisions. Statistically, the defensible reading is limited to the posted mean comparison and its uncertainty: the estimated average contrast was centered at 0.0, while the interval remained compatible with differences in either direction.

14. Why This Trial Matters Statistically

This trial is statistically informative because it makes the contrast explicit: both groups received lifestyle counseling, while only one arm also received PAP therapy. That design focuses the primary comparison on the addition of PAP within the study’s care context. Random allocation supports a comparative interpretation, although the registry does not report the sequence-generation or allocation-concealment details needed to assess those procedures fully.

The endpoint is a continuous change measure, summarized with a mean and standard deviation in each arm and a mean difference between arms. Reading these quantities together is important: the point estimate describes the observed average contrast, the standard deviations describe individual variability, and the confidence interval communicates uncertainty around the contrast. They answer related but distinct statistical questions.

The record also illustrates why analysis-population definitions matter. The primary outcome includes participants with at least one follow-up HbA1c measurement as well as a baseline value. That rule is relevant to interpretation because outcome availability determines who contributes a change score. Without details on missingness, imputation, and sensitivity analyses, the effect of unavailable follow-up data cannot be assessed from the registry record.

Finally, a null-centered estimate and a p-value of 1.0 do not prove no effect or equivalence. The interval and the absence of a reported equivalence margin are essential context. The record therefore supports careful interpretation of one primary comparison, while leaving important questions about precision, missing data, secondary outcomes, and the statistical analysis plan unresolved.

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 registry lists the trial as unmasked. In general, lack of masking can influence behavior, co-interventions, or outcome assessment, although HbA1c is a laboratory measure. The record does not report whether laboratory assessors were masked or describe procedures intended to reduce assessment bias.

The primary endpoint analysis is defined by availability of baseline and follow-up HbA1c measurements. The record does not report the number or reasons for missing follow-up values, a missing-data method, or sensitivity analyses. As a result, it is not possible to assess from the posted information whether the endpoint analysis population differed from all randomized participants in ways relevant to the outcome.

The registry does not provide the detailed statistical analysis plan, statistical test, covariate adjustment, confidence level, multiplicity procedure, or analysis-population designation. It also does not report the randomization method, allocation concealment, baseline characteristics, or treatment adherence. These omissions limit assessment of the analysis and of how comparable the groups were at baseline.

Only the primary endpoint result is posted; secondary results described in the study objectives are not reported in the registry record. No clinical threshold for interpreting the magnitude of an HbA1c difference is given. The arm means and standard deviations are rounded summaries, and participant-level distributions are not reported. These limitations do not invalidate the posted comparison, but they constrain what can be concluded from it.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: GLYCOSA Study:Effect of PAP Treatment on Glycemic Control in Patients With Type 2 Diabetes — NCT00509223.
• Registry record last updated 2013-12-30; status last verified 2013-12.
• Results first posted 2013-10-17.
• 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

NCT00509223 is a completed randomized, parallel-group study sponsored by ResMed, with no masking recorded. It enrolled 416 participants and compared lifestyle counseling with PAP therapy against lifestyle counseling without PAP therapy in patients with type 2 diabetes and obstructive sleep apnea.

The primary endpoint was mean change in HbA1c from baseline to Month 6. The posted mean change was -0.1 in each arm, with a reported mean difference of 0.0 and an unadjusted p-value of 1.0. The confidence interval includes zero. The outcome analysis included participants with baseline and at least one follow-up HbA1c measurement.

No secondary results or detailed statistical analysis plan are reported in the registry record. Missing-data methods, multiplicity handling, and an equivalence margin are also not reported.