Cocoa to Improve Walking Performance in Peripheral Artery Disease: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Cocoa to Improve Walking Performance in Peripheral Artery Disease (NCT02876887), a randomized na study. The primary outcome is Change From Baseline in Six-minute Walk Distance.

2. Clinical Question

The trial's central question concerns change in walking distance, measured in meters, rather than a diagnosis or a time-to-event outcome. Participants followed a standardized protocol in which they walked up and down a 100-ft hallway for 6 minutes after being instructed to cover as much distance as possible. The record identifies this as the primary outcome and also lists measures of maximal and pain-free treadmill walking time, physical activity, vascular function, and calf muscle characteristics as secondary outcomes.

The registry record does not report the observed change in distance in either group, a between-group estimate, confidence limits, or a statistical test result. Therefore, the direction, size, and precision of the difference between groups cannot be assessed from the primary outcome information in the record. The question is clear from the design, but the posted registry information does not give the numerical result needed to answer it.

3. Trial Design

The trial is listed as randomized, quadruple-masked, and parallel-group. Random allocation is intended to make treatment groups comparable on average at the point of assignment, including for characteristics that may not be measured. It does not guarantee that every feature will be balanced in a trial of this size. A parallel-group design assigns participants to a study group and follows that group over the intervention period rather than having each participant receive both beverages in sequence.

The registry record lists an enrollment of 44 and a completed status. The intervention period was six months. Participants in the cocoa group were assigned three servings per day of epicatechin-rich cocoa beverages, described as containing 75 mg daily; the placebo group received three servings per day of placebo beverages. The record lists Northwestern University as the sponsor and identifies the condition as peripheral artery disease. It lists the phase as NA.

Quadruple masking indicates that the trial record uses that masking designation, but the specific roles included in the designation are not reported in the registry record. Details of the randomization sequence, allocation concealment, beverage matching, adherence, and the procedures used to assess whether masking was maintained are not reported in the registry record. These details can matter when judging the risk of biased treatment assignment, differences in co-interventions, or outcome assessment.

The primary outcome was change from baseline in six-minute walk distance, assessed through six-month follow-up. The record describes two measurements after the final beverage dose: one 2-3 hours after the dose and one 24 hours after it. It does not state how those two measurements were to be combined, whether one was designated as the main primary comparison, or how both were handled statistically. That distinction matters because multiple measurements can represent separate questions or repeated observations of a single endpoint.

The registry lists seven outcome measures, but reports zero analyses. The exact analysis population, the statistical model, covariate adjustment, handling of missing follow-up values, and prespecified treatment contrast are not reported in the registry record. Randomization and masking describe important design features; they do not by themselves establish how the outcome data were analyzed or what effect estimate was obtained.

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

Analysis population for the primary outcome, as defined in the registry: Nineteen and 21 study participants in the cocoa and placebo groups, respectively, completed the six-minute walk at both baseline and 6-month follow-up.

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 Six-minute Walk Distance, measured over Change from baseline to six-month follow-up. Note - There will be two measures: One 2-3 hours after the final study beverage dose and one 24 hours after the final dose..

The primary endpoint is change from baseline in six-minute walk distance, measured in meters, through six-month follow-up. The test asks participants to walk up and down a 100-ft hallway for 6 minutes, following instructions to cover as much distance as possible. It is a measure of functional walking performance under a standardized task. A change score compares a participant's follow-up distance with that participant's baseline distance, so it focuses on change during the study rather than simply comparing follow-up distances without regard to baseline.

As a general statistical matter, a standardized performance measure can make outcomes more comparable across participants than an unstructured assessment. The result still depends on consistent test administration and on how observations are summarized and compared. Change scores can also be affected by measurement variability at baseline and follow-up; the precise analysis approach matters when estimating a group contrast.

The record specifies two six-month measurements, one 2-3 hours after the final dose and one 24 hours after the final dose. They are not interchangeable by definition: they reflect measurement at different times relative to the last beverage. The registry record does not report how the two measurements relate to one another or how they enter the primary analysis.

The endpoint's stated dispersion is a 90% confidence interval, but the registry record does not report the estimate or the interval limits. It therefore does not show the observed change in either group or the uncertainty around a cocoa-versus-placebo contrast. The number of participants reported as completing the walk at both baseline and follow-up is 19 in the cocoa group and 21 in the placebo group.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Statistical interpretation depends on both the design and the analysis. The trial is described as randomized, quadruple-masked, and parallel-group. In general, randomization uses chance to allocate participants and is intended to reduce systematic differences between groups at the start of a study. Masking is intended to limit the influence of treatment knowledge on participant behavior, care, or outcome assessment, depending on which people are masked. The registry record does not report the specific masking roles or the detailed randomization procedures.

What does a change score represent?

The primary outcome is change from baseline in six-minute walk distance. In general, a change score is calculated for each participant by comparing a follow-up measurement with that participant's baseline value. Group-level summaries can then describe average change, and a treatment contrast can compare those summaries. The record does not report whether the primary analysis used change scores directly, adjusted follow-up values for baseline, or used another model. These approaches can differ in their assumptions and precision, so the precise method should not be inferred from the endpoint title.

The endpoint is described as a mean with a 90% confidence interval. In general, a mean summarizes the central tendency of measurements, while a confidence interval describes uncertainty around an estimated quantity under the analysis assumptions. A confidence interval for a group mean and one for a between-group contrast answer different questions. The registry record does not give the estimate or interval limits, and it does not specify whether the listed dispersion applies to each group separately or to a comparative effect.

Why is the comparison more important than separate group summaries?

The clinical question compares cocoa with placebo. In general, the central randomized-trial estimand is a contrast between assigned groups, not whether one group's within-group change differs from zero while another group's change does not. Separate group summaries can help describe observed trajectories, but they do not by themselves quantify the randomized comparison. The registry record does not report a comparative estimate or its confidence interval, so the treatment contrast cannot be interpreted numerically.

Statistical significance and effect size are also distinct concepts. A p-value, when reported, evaluates data against a specified null model and depends on the analysis assumptions; it is not a measure of clinical importance or the probability that a treatment works. An effect estimate describes the size and direction of the contrast, while its interval communicates precision. No p-value or estimate is reported for the primary outcome in the registry record, so neither statistical significance nor magnitude can be assessed.

What does the timing of the walk tests imply?

The record describes two six-month assessments relative to the final beverage dose: one 2-3 hours afterward and one 24 hours afterward. Repeated or differently timed measurements can address distinct questions. A nearer measurement and a later measurement may reflect different time windows, but the registry record does not state the intended interpretation of that timing, the expected pattern, or the statistical handling. It would be inappropriate to assume that one is an acute measure and the other a lasting measure without a stated analysis plan. The record also does not explain whether the two observations were treated as co-primary outcomes, repeated measurements, or separate outcomes.

What is not known about the statistical plan?

The registry record does not report a statistical analysis plan, model specification, covariates, assumptions, significance threshold, or multiplicity procedure. It also does not report whether analyses were intention-to-treat, per-protocol, or based on another population. These omissions prevent a full assessment of how the study intended to estimate the treatment effect, what assumptions supported the analysis, or how protocol deviations were handled. The absence of analysis details should not be filled in by assuming common practice.

In general, model assumptions should be considered in relation to the outcome distribution and design. A model for a continuous distance measure may summarize average differences, but its adequacy depends on features such as residual behavior and influential observations. If the data are skewed or show unequal variability, the chosen model and uncertainty calculation can affect inference. The record does not provide diagnostic information or enough outcome data to evaluate these issues.

Sample-size calculations are planning tools, not observed results. A planning illustration based on an observed effect would be a retrospective calculation and would not establish the trial's original design rationale or observed power. The registry record does not report the original sample-size justification. No power or sample-size conclusion should therefore be attributed to the investigators on the basis of the design information alone.

Finally, reporting of an endpoint's name, unit, timeframe, and dispersion format is not equivalent to reporting its outcome. For interpretation, a reader would need the group estimates, the comparative contrast, interval limits, the analysis population, and the method used to address missing measurements. Those results and methods are not reported in the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists seven outcome measures. It also describes two six-month primary-outcome measurements, taken at different intervals after the final beverage dose. When several outcomes or time points are examined, there may be multiple opportunities to find an apparently notable result. As a general statistical matter, multiplicity procedures can define which comparisons are primary and can adjust inference when appropriate. The registry record does not report a multiplicity strategy or explain how the two walk-test time points were prioritized or combined.

The record reports zero analyses and does not provide results for the primary or secondary outcomes. It does not report the analysis population, whether all randomized participants were included, or whether any exclusions occurred. It also does not explain how missing outcome measurements were handled. These details are important because an analysis limited to participants with observed follow-up data can differ from one that uses a broader randomized population, especially if missingness is related to prognosis or treatment experience.

The primary-outcome description states that 19 participants in the cocoa group and 21 in the placebo group completed the six-minute walk at both baseline and six-month follow-up. The enrollment entry is 44. The record does not explain the difference between the enrolled population and the paired-measurement population, or state whether missing values were imputed, modeled, or omitted. No assumption about the reason for missing measurements or their statistical treatment can be made from the record.

The registry record also does not describe prespecified subgroup analyses, interim analyses, or adjustments for baseline covariates. These matters are not reported in the registry record. Without the analysis plan and numerical results, readers cannot determine how many comparisons were actually conducted or whether the reported primary question was analyzed as planned.

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.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: dyspnea (4.8%), cough (4.8%), hospitalization for depression (4.3%), death (4.3%), lower extremity revascularization (4.3%).

The registry record lists 23 participants at risk in the cocoa group and 21 in the placebo group for the serious adverse event summary. It reports 7 affected in the cocoa group and 2 affected in the placebo group. The record reports 0 other adverse events in each group. These are descriptive counts; without additional information, they do not establish whether an event was caused by a study beverage or whether the groups differed statistically.

The registry lists one death in the cocoa group and zero in the placebo group. The listed serious-event terms include Dyspnea at 4.8%, Cough at 4.8%, Hospitalization for depression at 4.3%, Death at 4.3%, Lower extremity revascularization at 4.3%, and Food ulcer with cellulitis at 4.3%. Those listed terms should be read as registry entries, not as evidence of a causal relationship. The relationship of each event to the intervention is not reported in the registry record.

Serious adverse event counts and the number of participants with an event are different summaries in general: a participant can potentially have more than one event. The registry record does not provide enough detail to determine the number of distinct events represented by every listed term or whether categories overlap. The safety figures also do not describe the primary walking-distance outcome. They should be considered separately from any assessment of comparative functional performance.

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

The record establishes that a randomized, quadruple-masked, parallel-group trial compared six months of cocoa beverages with placebo beverages in people with peripheral artery disease. It identifies change in six-minute walk distance as the primary outcome and describes the standardized walking test and the two measurement times relative to the final dose. These details define the study question and its measurement framework.

The registry record does not report the primary outcome estimates, the between-group contrast, confidence interval limits, or a p-value. It therefore does not show whether mean walking distance changed differently between groups, how large any difference was, or how precise an estimate might be. The lack of a reported result should not be interpreted as a finding of no difference, and it does not establish benefit or lack of benefit.

The endpoint is one measure of walking performance. The record also lists secondary outcomes that assess treadmill walking, physical activity, vascular function, and calf muscle characteristics. Those are related but distinct measures; a result on one would not automatically establish the same pattern on another. Their results are not reported in the registry record.

The serious adverse event entries describe events recorded in each group, including the reported death count. They do not establish that the intervention caused or prevented any event. Causal interpretation would require more information about event definitions, timing, relatedness assessments, follow-up, and comparative uncertainty than the registry record reports.

In general, conclusions from a clinical trial should distinguish the observed estimate from uncertainty, analysis choices, and the limits of the population and outcome studied. Here, the design and endpoint can be described, but the missing results preclude a statistical conclusion about the primary comparison. The registry record alone does not support a claim about treatment efficacy or a clinical recommendation.

13. Why This Trial Matters Statistically

This trial raises several important statistical issues in a relatively compact design. First, it uses a randomized comparison, making the between-group contrast the key target for interpretation. The relevant evidence would be the estimated difference in change in six-minute walk distance and its uncertainty, rather than a comparison of whether each group changed from baseline in isolation. The registry record does not report that contrast.

Second, the primary outcome includes two measurements at six-month follow-up, at different times after the final dose. Defining the primary estimand requires clarity about whether those measurements answer separate questions or are combined in a specified way. The registry record gives the timing but not the analysis strategy. This illustrates why outcome definitions must include both what is measured and how multiple measurements contribute to inference.

Third, the record reports participants with paired baseline and follow-up walk assessments, while also reporting a larger enrollment figure. Transparent accounting of analysis populations and missing measurements is essential because the treatment comparison can depend on who contributes data and how missingness is handled. Those details are not reported in the registry record.

Finally, multiple outcomes create a need to distinguish a prespecified primary question from secondary or exploratory findings. The registry lists several outcome measures but does not report results or a multiplicity plan. This makes it impossible to assess the coherence of outcome reporting or the uncertainty associated with multiple testing. Taken together, the record illustrates that design labels and endpoint descriptions are not a substitute for estimates, analysis methods, and transparent reporting.

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 most important limitation of the registry information is that it does not report numerical results for the primary outcome. The mean change in each group, comparative estimate, confidence interval limits, and statistical test result are absent. This prevents assessment of effect direction, magnitude, and precision.

The endpoint includes two measurement times after the final study beverage dose, but the registry record does not explain their analytic relationship. It does not state whether both were separately analyzed, whether one was prioritized, or whether a combined measure was used. The statistical plan and outcome definitions for those measurements are not reported in the registry record.

The record reports that 19 cocoa-group participants and 21 placebo-group participants completed the six-minute walk at both baseline and six-month follow-up. It does not explain missing assessments, withdrawals, adherence, protocol deviations, or the analysis population. Consequently, the potential impact of incomplete outcome data cannot be evaluated. The original sample-size justification and the details of the randomization and masking procedures are also not reported in the registry record.

Seven outcome measures are listed, but no analysis results or multiplicity approach are reported. It is therefore not possible to assess whether all outcomes were reported as planned or how uncertainty from multiple comparisons was addressed. The record's serious adverse event entries are also limited: the registry does not report event relatedness, detailed timing, or enough information to establish causation.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Cocoa to Improve Walking Performance in Peripheral Artery Disease — NCT02876887.
• Registry record last updated 2020-08-06; status last verified 2020-07.
• Results first posted 2020-08-06.
• 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

The record describes a completed randomized, quadruple-masked, parallel-group trial sponsored by Northwestern University, with enrollment recorded as 44. The study compared three daily servings of epicatechin-rich cocoa beverages, containing 75 mg daily, with three daily servings of placebo beverages over six months in people with peripheral artery disease.

The primary outcome was change from baseline in six-minute walk distance, measured in meters, with two six-month measurements described relative to the final beverage dose. The record reports that 19 participants in the cocoa group and 21 in the placebo group completed the walk at both baseline and follow-up. It lists seven outcome measures and reports zero analyses.

Primary and secondary outcome estimates, confidence interval limits, p-values, analysis methods, and missing-data procedures are not reported in the registry record. The safety summary lists serious adverse events in both groups, including one death in the cocoa group and none in the placebo group, without reported causal attribution.