MK0431A Comparative Study in Patients With Type 2 Diabetes (0431A-079)(COMPLETED): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for MK0431A Comparative Study in Patients With Type 2 Diabetes (0431A-079)(COMPLETED) (NCT00482729), a randomized phase 3 study. The primary outcome is Change From Baseline in Hemoglobin A1c (A1C) at Week 18.

2. Clinical Question

The question is about the measured change over the specified period and the uncertainty around the group comparison. A negative change means the Week 18 A1C value was below the Week 0 value on the stated scale. The primary result is not simply a comparison of the two arm estimates: the registry also reports a model-based, adjusted comparison using ANCOVA. Its confidence interval describes uncertainty in that estimated difference under the analysis used.

The record lists two secondary outcomes: the number of patients with A1C < 7.0% at Week 18 and change from baseline in fasting plasma glucose at Week 18. Those outcomes provide other measures of glycemic status, but the primary question addressed is the continuous A1C change. The record does not report additional detail about how the secondary outcomes were analyzed in the registry record.

3. Trial Design

This was a Phase 3, randomized, double-blind, active-comparator controlled clinical trial with a parallel-group model. It compared Sita/Met FDC with metformin in patients with type 2 diabetes mellitus. The registry title identifies the study as completed. The listed enrollment was 1246.

The record lists the study start as 2007-06-19 and primary completion as 2008-11-03. Its purpose was to investigate the efficacy and safety of an investigational treatment for type 2 diabetes mellitus. The intervention list names sitagliptin phosphate (+) metformin hydrochloride and metformin; the primary outcome groups are titled Sita/Met FDC and Metformin. The record does not report dosing details in the registry record.

Random allocation is intended to reduce systematic differences between treatment groups at the point of assignment. Double masking means the study was designed so that treatment knowledge was concealed from relevant parties, although the registry entries do not specify exactly who was masked or how masking was maintained. A parallel design compares groups followed under their assigned treatments rather than describing a crossover between treatments.

For the primary endpoint, the registry lists 559 patients in the Sita/Met FDC group and 564 in the metformin group. These are the counts attached to the endpoint estimates, and should not be confused with the overall enrollment. The safety record separately lists 625 and 621 patients at risk in the respective groups. These different counts are recorded for different analyses; the registry entries do not explain the reasons for the differences, so they should not be reconciled by assumption.

The study was sponsored by Merck Sharp & Dohme LLC. Further information about allocation procedures, treatment adherence, study-site organization, sample-size justification, or interim analyses is 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: Patients 18-78 years of age with type 2 diabetes mellitus (T2DM) with inadequate glycemic control (hemoglobin A1c \[A1C\] \>7.5% at screening visit) who were appropriate for treatment with oral antihyperglycemic therapy and had not been on an anti-hyperglycemic agent (AHA) in the last 4 months were eligible to participate.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: The Full Analysis Set (FAS) included all patients who received at least 1 dose of double-blind study therapy, had a baseline value and ≥ 1 post-baseline value for this outcome. Data after initiation of additional AHA were treated as missing. For FAS with no data at Week 18, the last post-baseline observed measurement was carried forward to Week 18.

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 Change From Baseline in Hemoglobin A1c (A1C) at Week 18, measured over Baseline and Week 18.

The primary endpoint was change from baseline in hemoglobin A1C (A1C) at Week 18, measured as a percent. The registry defines change as Week 18 A1C minus Week 0 A1C. The reported arm estimates are least-squares means, a model-based form of the group mean, with 95% confidence intervals.

A1C is used as a measure of glycemic status over time. A change endpoint describes how the measured value at follow-up differs from the baseline value, rather than reporting only the follow-up level. This can make the result easier to interpret in relation to the starting measurement, though the registry entries do not provide baseline values or details of the model beyond the reported ANCOVA comparison.

The arm estimates were -2.37 for Sita/Met FDC and -1.76 for metformin. Because the change is follow-up minus baseline, negative values represent decreases on the A1C percent scale. The arm confidence intervals indicate the precision of each least-squares mean estimate; they are not ranges containing every individual patient's change.

The endpoint's analysis population was the Full Analysis Set. Patients had to have received at least 1 dose of double-blind study therapy and have both a baseline value and at least 1 post-baseline value for the outcome. The record also states that data after initiation of additional AHA were treated as missing. The more detailed rule for handling FAS participants without Week 18 data is not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: each participant's change in A1C is measured on a numeric scale, and the analysis compares group averages. This differs from a binary outcome, which would classify each participant into one of a limited set of categories. A continuous measure preserves information about the size and direction of each observed change, although the registry does not provide the distribution of individual changes.

What does a least-squares mean represent?

A least-squares mean is a model-based estimate of a group mean. It is often described as an adjusted mean because it can account for terms included in the statistical model. The registry identifies the arm estimates as least-squares means and identifies ANCOVA as the method for the between-group analysis. It does not report the model's covariates or other specification details in the registry record, so the exact adjustments cannot be described.

The reported arm values are -2.37 for Sita/Met FDC and -1.76 for metformin. The registry reports 95% confidence intervals for each estimate. These intervals convey the uncertainty associated with estimating the arm means under the analysis; they do not show the range of observed participant-level changes. Since they are estimates from a model, they should not be treated as raw arithmetic averages unless the record says that is how they were obtained.

How should the ANCOVA comparison be read?

ANCOVA, or analysis of covariance, compares an outcome between groups while including one or more covariates in a model. In general, this can improve precision or account for differences associated with those covariates. The registry names ANCOVA and reports a mean difference (net), but the specific covariates and model details are not reported in the registry record. It would therefore be inappropriate to infer which baseline factors were included or how they were handled.

The reported estimate is -0.60, with a 95% confidence interval from -0.78 to -0.43 and p < 0.001. The estimate is the sponsor's stated model-based comparison, not an independently derived calculation from the two arm means. The two estimates and the between-group result can differ slightly in presentation because of model adjustment and rounding; the registry's stated comparison should be interpreted as its own analysis rather than replaced with a manually calculated contrast.

What do the confidence interval and p-value add?

A confidence interval describes the precision of an estimate under the analysis assumptions. A narrower interval indicates less statistical uncertainty than a wider interval for the same scale and setting, but does not remove concerns about bias, missing data, model specification, or outcome selection. The interval for the mean difference gives readers a range of values compatible with the reported analysis, rather than only a single point estimate.

A p-value summarizes how inconsistent the observed data are with a specified null hypothesis, assuming that hypothesis and the model are correct. The registry reports p < 0.001 for the comparison. That threshold should not be read as the probability that treatment has no effect, as a measure of clinical importance, or as a guarantee that an estimate will replicate. The confidence interval and estimated magnitude are needed to understand the result's scale and precision.

Why can over-dispersion matter?

Over-dispersion is a general issue for outcomes such as counts or binary events when the observed variability exceeds what a simple statistical model assumes. If not addressed, standard errors and confidence intervals can be too optimistic. It is not a reported feature of this continuous A1C endpoint, and the registry entries do not describe an over-dispersion analysis. The concept is relevant to statistical interpretation generally, but should not be attributed to this trial's primary analysis.

What does a planning sample size mean?

Sample-size planning asks how many participants might be needed to detect a specified effect under chosen assumptions. The planning assumptions associated with this trial describe a two-sided significance level of 0.05, equal allocation, a normal approximation, and an effect defined as a stated fraction of the observed effect. These are planning illustrations based on the observed effect, not the trial's own design justification. Such illustrations are not observed power and do not establish what power the completed trial actually had. The trial's own sample-size justification is not reported in the registry record.

In general, a sample-size estimate depends on the target effect, variability, allocation, statistical test, significance level, and desired power. Changing any assumption can change a planning estimate. An estimate based on a fraction of an observed effect is retrospective and illustrative; it does not show that the trial was originally designed around that effect. The registry entries do not include numerical planning participant counts, so none can be interpreted.

What is known about the analysis population?

The Full Analysis Set included patients who received at least 1 dose of double-blind study therapy and had a baseline value and at least 1 post-baseline value for this outcome. This definition specifies who could contribute to the endpoint analysis. The registry states that data after initiation of additional AHA were treated as missing. The description of what happened for FAS participants without Week 18 data is incomplete in the available record; the exact imputation or missing-data procedure is not reported in the registry record.

Missing-data handling matters because the result can depend on how unavailable measurements are treated. Complete-case analysis, imputation, or model-based approaches can rely on different assumptions. General statistical reasoning can explain these options, but the registry entries do not establish which complete procedure was used for every missing Week 18 measurement. It would be inappropriate to infer a particular method from the partial description.

The registry's result should therefore be read as a model-based comparison for the stated FAS population and endpoint, accompanied by the reported intervals and p-value. The registry entries identify the broad method and analysis population but do not specify every model term, assumption, multiplicity adjustment, or missing-data procedure.

10. Analyses Reported by the Sponsor

The registry reports the sponsor's primary comparison as an ANCOVA mean difference (net) of -0.60, with a 95% confidence interval from -0.78 to -0.43 and p < 0.001. This is the trial's stated analysis and should be distinguished from a simple unadjusted calculation using arm-level summary values. ANCOVA can account for model terms that are not visible in the arm summaries; the specific terms are not reported in the registry record.

The listed arm estimates are least-squares means, rather than values explicitly identified as raw means. The registry entries do not include a separate recalculated two-arm comparison for this continuous endpoint. Consequently, there is no independent simple recalculation to use in place of the sponsor's model-based result. The registry's discrepancy indicator is false; no discrepancy between a sponsor result and a recalculation is flagged.

The sponsor's estimate remains a statistical estimate, not a statement of clinical importance or a guarantee of similar outcomes in other settings. Its confidence interval and p-value should be read in the context of the specified Week 18 A1C change, the Full Analysis Set, and the reported ANCOVA approach. The analysis details needed to reproduce the model are not reported in the registry record.

11. Multiplicity, Missing Data and Analysis Populations

The registry lists five outcome measures and five analyses, and identifies the primary endpoint as change from baseline in A1C at Week 18. It also lists two secondary outcomes: the number of patients with A1C < 7.0% at Week 18 and change from baseline in fasting plasma glucose at Week 18. The registry entries do not describe the other listed measures or analyses in detail.

When a study tests multiple outcomes or makes multiple comparisons, the chance of obtaining at least one small p-value by chance can increase. Statistical procedures for controlling multiplicity can address that issue, but the registry entries do not report whether an adjustment was applied, which outcomes were included in any testing hierarchy, or whether the secondary outcomes were formally confirmatory. The reported p-value should therefore be understood as the value attached to the stated primary comparison, without assuming a multiplicity adjustment or its absence.

The primary analysis population was the Full Analysis Set, defined as patients who received at least 1 dose of double-blind study therapy and had a baseline and at least 1 post-baseline value for this outcome. The registry entries state that data after initiation of additional AHA were treated as missing. They also include a partial description of handling for FAS participants without Week 18 data, but do not provide the complete procedure. The exact missing-data method for those participants is not reported in the registry record.

Missingness can affect estimates when the availability of a measurement is related to the outcome or to factors associated with it. General methods may make assumptions about why data are missing, but the registry entries do not describe such assumptions or sensitivity analyses. The endpoint estimates should be interpreted with this reporting gap in mind.

There is no basis in the registry entries to infer interim analyses, a prespecified testing hierarchy, or a detailed statistical analysis plan. Those details are not reported in the registry record. The record also does not explain the difference between the endpoint analysis counts and the safety counts; those figures refer to separate reported analyses and should not be treated as interchangeable.

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: any cardiac disorders (1.0%), any infections and infestations (1.0%), any neoplasms benign, malignant and unspecified (incl cysts and polyps) (0.8%), any nervous system disorders (0.8%), any vascular disorders (0.6%).

The safety record lists 625 patients at risk in the Sita/Met FDC group and 621 in the metformin group. Serious adverse events affected 28 and 38 patients, respectively. Other adverse events affected 173 and 185 patients, respectively. These are the counts recorded for the stated groups; no additional interpretation of event severity, duration, or relatedness is reported in the registry record.

The record also lists serious-event terms and their reported percentages: Any Cardiac Disorders, 1.0%; Any Infections and Infestations, 1.0%; Any Neoplasms benign, malignant and unspecified (incl cysts and polyps), 0.8%; Any Nervous System Disorders, 0.8%; Any Vascular Disorders, 0.6%; and Coronary artery disease, 0.5%. These entries describe reported categories or terms, not necessarily mutually exclusive groups. The registry entries do not provide enough detail to determine overlap, event counts for each term, or how the categories were selected.

Deaths are not reported in the registry record. Safety counts are descriptive and should not be interpreted as proving that one treatment caused or prevented an event. Differences in counts alone do not establish a statistically reliable safety difference; the registry entries do not report a formal comparison or uncertainty interval for these safety outcomes. The at-risk counts also differ from the counts attached to the primary endpoint, and the reason is not reported.

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

The primary result describes the estimated change in A1C from baseline to Week 18 in the two reported treatment groups, and the model-based comparison between them. Both arm estimates are negative: -2.37 for Sita/Met FDC and -1.76 for metformin. The reported ANCOVA mean difference (net) is -0.60, with a 95% confidence interval from -0.78 to -0.43 and p < 0.001.

These statistics convey direction, estimated magnitude, and statistical precision for the defined endpoint. They do not show the distribution of individual responses, nor do they establish that every participant experienced a decrease. A group mean can differ from the experience of any particular participant. The confidence interval describes uncertainty in an estimated group comparison under the analysis assumptions, not a prediction interval for individual outcomes.

The result is specific to A1C change at Week 18, the stated Full Analysis Set, and the reported ANCOVA analysis. It does not answer questions about long-term outcomes, other patient groups, all secondary outcomes, or outcomes not listed in the registry entries. It also does not establish the clinical importance of the estimated difference; the registry entries do not provide a threshold for interpreting clinical importance.

A statistically small p-value does not by itself establish clinical importance, eliminate uncertainty, or show that a finding will reproduce in another study. Conversely, a confidence interval does not address every possible source of bias. The incomplete reporting of the missing-data procedure, model specification, multiplicity handling, and other analysis details limits how fully the result can be independently evaluated.

The safety counts offer descriptive information about serious and other adverse events in the listed groups. Without a reported formal safety comparison, details about event attribution, and complete information on deaths, the figures do not establish a causal safety advantage or disadvantage. The appropriate conclusion is limited to what was reported: group-level Week 18 A1C estimates and a sponsor-reported statistical comparison, alongside the recorded safety counts.

14. Why This Trial Matters Statistically

This trial illustrates why an endpoint estimate and a between-group comparison are related but distinct pieces of evidence. The arm-level least-squares means describe estimated within-group changes, while the ANCOVA mean difference addresses the contrast between groups under the reported model. Reading both helps distinguish change over time in each group from the treatment-group comparison that answers the primary statistical question.

It also highlights the importance of naming the analysis population. The Full Analysis Set definition explains that participants needed a dose of double-blind study therapy and baseline and post-baseline endpoint data. The record further states that measurements after initiation of additional AHA were treated as missing. Those choices affect which information informs the analysis and make complete reporting of missing-data procedures important.

The reported confidence interval contributes information that a p-value alone cannot provide. The interval shows the precision of the mean-difference estimate under the analysis, while the p-value addresses compatibility with the specified null hypothesis. Neither statistic alone establishes clinical importance or removes uncertainty about model assumptions and trial conduct.

The record also demonstrates the need to distinguish endpoint counts from safety denominators. The primary endpoint estimates and safety summaries are reported with different counts. Without an explanation of the difference, readers should not infer a cause or assume the denominators describe the same population.

Finally, the registry describes a randomized, double-blind, Phase 3 comparison and reports a model-based primary result, but leaves important analytic details unreported. Recognizing both what the record establishes and what it does not establish is central to sound statistical interpretation.

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 entries do not report the ANCOVA model's covariates, other specification details, or the procedure used to produce the adjusted comparison. This limits independent reproduction of the sponsor's estimate. The arm estimates are identified as least-squares means, but the registry entries do not give the model details needed to understand every adjustment reflected in them.

The missing-data description is incomplete. The record states that data after initiation of additional AHA were treated as missing and defines the Full Analysis Set, but the exact handling of FAS participants without a Week 18 measurement is not reported in the registry record. Sensitivity analyses for missing data are also not reported in the registry record.

Multiplicity procedures are not described in the registry entries. Although the registry lists five outcome measures and five analyses and identifies two secondary outcomes, it does not report a testing hierarchy or whether the primary p-value was adjusted for multiple testing. The interpretation of the reported p-value should not assume an unreported procedure.

The registry entries do not explain why the primary endpoint arm counts, 559 and 564, differ from the safety at-risk counts, 625 and 621. These counts relate to different reported analyses, but the reasons for their difference are not reported in the registry record. The registry entries also do not provide detailed baseline characteristics, adherence information, or the numerical details of the planning illustrations.

The record does not report deaths, formal statistical comparisons for the safety outcomes, or event attribution details. It also does not provide longer-term primary endpoint results or enough detail to assess the listed secondary outcomes fully. These limits restrict interpretation to the stated Week 18 A1C analysis and the descriptive safety counts.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: MK0431A Comparative Study in Patients With Type 2 Diabetes (0431A-079)(COMPLETED) — NCT00482729.
• Registry record last updated 2017-06-09; status last verified 2017-05.
• Results first posted 2010-03-15.
• 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

NCT00482729 is a completed Phase 3 randomized, double-blind, active-comparator, parallel-group trial sponsored by Merck Sharp & Dohme LLC. It compared Sita/Met FDC with metformin in patients with type 2 diabetes mellitus. Enrollment was 1246; the study started on 2007-06-19, with primary completion on 2008-11-03.

The primary endpoint was change from baseline in A1C at Week 18. The reported least-squares mean changes were -2.37 for Sita/Met FDC and -1.76 for metformin. The sponsor-reported ANCOVA mean difference (net) was -0.60, with a 95% confidence interval from -0.78 to -0.43 and p < 0.001. The registry also reports serious and other adverse-event counts, but the registry entries do not include deaths or a formal safety comparison.

Important analysis details, including full model specification, complete missing-data procedures, and multiplicity handling, are not reported in the registry record.