Effect of Probiotic Supplementation on Endothelial Function: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Effect of Probiotic Supplementation on Endothelial Function (NCT01952834), a na phase 4 study. The primary outcome is Brachial Artery Flow Mediated Dilation.

2. Clinical Question

The study’s stated purpose was to examine whether probiotic supplementation affects blood-vessel function in people with coronary artery disease. It also planned blood measurements for markers of inflammation, and the registry lists Interleukin 8 and Interleukin-12 as secondary outcomes. Those aims provide context, but they do not substitute for numerical outcome results.

The registry describes a completed phase 4 study sponsored by the Medical College of Wisconsin. Its nonrandomized, single-group structure makes the central question a before-and-after one: whether the recorded endpoint changed during the probiotic period. Without a control group and posted endpoint estimates, the record cannot establish how any change compares with what might have occurred over the same period without probiotic supplementation.

3. Trial Design

The registry identifies NCT01952834, titled “Effect of Probiotic Supplementation on Endothelial Function,” as a completed phase 4 study. The official title specifies men with coronary artery disease. The recorded enrollment is 21. The study began in 2013-06 and had primary completion in 2015-03. These are registry dates; they do not provide the timing of each participant’s measurements.

The design is listed as single group, with allocation recorded as NA and masking as none. This means the registry does not describe random assignment to parallel treatment groups or masked assessment. A no-masking design does not, by itself, show that any particular measurement was biased; it does mean that the record does not document masking as a safeguard against expectations affecting treatment or assessment.

The intervention description lays out a sequence: GoodBelly probiotic, 2.7 oz daily for 6 weeks; a 4 week washout; and then vancomycin, 250 mg four times daily orally for 10 days. The registry’s brief summary calls the vancomycin study optional. The sequence should therefore not be read as evidence that all participants completed every period. Nor does the description give enough information to establish how the optional component was handled for each participant.

The primary outcome is brachial artery flow-mediated dilation, with a timeframe of percent change before and after 6 weeks of daily probiotic. The study description says blood-vessel function was measured by ultrasound before and after probiotic and vancomycin, and blood was taken to evaluate markers of inflammation. The listed secondary outcomes include Interleukin 8 and Interleukin-12. Numerical outcome results and participant-level completion information are not reported in the registry record.

Because the study has no randomized control comparison, its principal design can describe within-person change over time, if such results are reported. It cannot isolate treatment effects from temporal changes, measurement variability, or other factors that change during follow-up. The registry record does not report a statistical analysis plan, a sample-size justification, or whether an interim analysis was planned.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

Reasons for not completing this period:

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 Brachial Artery Flow Mediated Dilation, measured over % Change before and after 6 weeks of daily Probiotic.

Brachial artery flow-mediated dilation is a measure of endothelial function. The registry describes the endpoint as the percent change in brachial artery diameter in response to a flow stimulus induced by 5 minutes of occlusion of flow to the arm. The diameter change is measured from baseline diameter. The primary endpoint timeframe is the change before and after 6 weeks of daily probiotic.

As a continuous measure, flow-mediated dilation captures the magnitude of a physiological response rather than classifying participants into categories such as improved or not improved. A mean can describe the average response in a group, while a standard deviation describes how spread out individual measurements are around that mean. These are general statistical interpretations of the mean and standard deviation; the registry record does not report the actual endpoint mean or standard deviation.

This measure is used to assess vascular function in humans. Its relevance to the study’s stated purpose is that it quantifies a vessel response to a flow stimulus. However, an endpoint’s physiological meaning is not the same as evidence of a treatment effect. Interpretation depends on the observed before-and-after results, their uncertainty, measurement procedures, and the design’s ability to distinguish an intervention-related change from other explanations.

The posted registry information identifies the measure and its timing but not the numerical result. The size and direction of any change, the precision of an estimate, and the number of participants contributing endpoint data are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies the primary outcome as a continuous measure summarized by a mean and standard deviation. These summaries answer different questions. The mean describes the average value in the analyzed group, while the standard deviation describes dispersion among observations. In a before-and-after study, researchers may focus on individual changes or on a group-level contrast between measurement times. The registry record does not report the calculation used for the primary outcome, the numerical summaries, or an analysis model.

What does a mean describe?

A mean is the arithmetic average of observed values. For this endpoint, it could describe the average brachial artery flow-mediated dilation at a particular measurement time or the average change between times, depending on the analysis definition. The endpoint description specifies percent change before and after 6 weeks of daily probiotic, but does not state whether a reported mean would be a mean of individual changes, a difference between group means, or an adjusted estimate. No such result is reported.

Why does the standard deviation matter?

The standard deviation reflects how much observations vary around their mean. It is not the same as the standard error, which quantifies uncertainty in an estimated mean. Greater variation generally makes an estimate less precise, all else being equal. In a repeated-measures design, the spread of individual changes and the relationship between measurements within a participant can matter. Those quantities and the method used to account for paired observations are not reported in the registry record.

How should a confidence interval be understood?

In general, a confidence interval describes the uncertainty around an estimate under the specified statistical model. It gives readers a range of effect sizes compatible with the observed data and assumptions. Its width conveys precision, but it does not account automatically for limitations such as nonrandom assignment, measurement bias, or selective reporting. The registry record does not report a confidence interval for the primary endpoint, so its precision cannot be described.

What would a p-value answer?

In general, a p-value assesses how compatible the observed data are with a statistical null model, assuming the model and its assumptions are appropriate. It does not measure the probability that a treatment works, nor does it describe the size or clinical importance of an effect. A p-value is most informative alongside an effect estimate and interval. No primary-outcome p-value or analysis is reported in the registry record; the record lists zero analyses.

Why does the design affect interpretation?

A single-group before-and-after study can examine whether measurements differ over time among those observed. Without a concurrent randomized comparator, it cannot separate a treatment-related change from other influences occurring over the same period. Randomization is a general method for balancing known and unknown factors between treatment groups, while masking can reduce some opportunities for expectations to influence care or assessment. This study lists allocation as NA and masking as none. Those design labels do not prove that a particular bias occurred, but they limit the strength of causal conclusions available from a simple before-and-after contrast.

The intervention sequence also matters for defining the estimand, the precise quantity an analysis aims to estimate. The primary endpoint timeframe refers to before and after the probiotic period. Vancomycin follows a washout and is described as optional. Without participant-level exposure and measurement details, an analysis cannot be assumed to represent a uniform sequence or to estimate an effect of the antibiotic period. The registry record does not describe how the optional period was included in any analysis.

What does over-dispersion mean generally?

Over-dispersion occurs when observed variability is greater than a statistical model assumes. It is especially relevant to count outcomes, where a simple model may underestimate uncertainty if counts are more variable than expected. The primary outcome in this study is continuous, not a count, and the registry does not report a model or evidence of over-dispersion. This general concept should not be mistaken for a finding about this trial.

What do the planning assumptions tell readers?

The registry information describes sample-size illustrations based on a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The target effect is defined as a stated fraction of the observed effect. These assumptions describe hypothetical planning exercises, not the design actually used: the trial is listed as single group and not randomized. A sample-size illustration is not observed power, and it does not show that a study had a particular probability of detecting its actual effect. The registry record does not report the trial’s own sample-size justification or planning assumptions.

Interpretation of any statistical result would also require knowing which participants and observations were included, how missing values were handled, and whether the method was selected before results were examined. These details are not reported in the registry record. Since numerical endpoint results are also absent, it is not possible to assess model fit, robustness, or whether the analysis corresponds to the stated endpoint timeframe.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("GoodBelly Probiotic and Vancomycin")
n   <- c(20)
m   <- c(1.2)
sp  <- c(1.6)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  GoodBelly Probiotic and Vancomycin  20  1.200  1.600  0.451  1.949

11. Multiplicity, Missing Data and Analysis Populations

Multiplicity arises when a study evaluates several outcomes, timepoints, or analyses. When many statistical tests are conducted, the chance of obtaining at least one apparently notable result can increase. General approaches include identifying a primary endpoint in advance, adjusting for multiple comparisons, or clearly labeling additional analyses as exploratory. The registry identifies brachial artery flow-mediated dilation as the primary outcome and lists Interleukin 8 and Interleukin-12 as secondary outcomes. It does not report a multiplicity strategy or numerical analyses for these measures.

The record describes blood-vessel measurements before and after probiotic and vancomycin, while the primary endpoint timeframe is tied to the probiotic period. It does not state how many timepoints or comparisons were included in any analysis, whether the optional antibiotic period was analyzed, or how tests across outcomes were handled. The registry lists zero analyses. A planned primary endpoint can help clarify which question is central, but it does not by itself show how multiple testing was managed.

Missing data can affect both the number of observations available and the interpretation of an estimate. The enrollment figure is 21, but the registry does not report the number with endpoint measurements at each timepoint, reasons for missing observations, or a method for handling them. It also does not report an analysis population definition, such as which participants were expected to contribute to the primary analysis. Enrollment should not be treated as the denominator for every endpoint analysis without that information.

The registry record does not report whether missing values were imputed, whether analyses used available observations, or whether sensitivity analyses assessed alternative assumptions about missingness. These omissions prevent readers from evaluating how incomplete follow-up may have affected precision or potential bias. No assumption about missingness or analysis population can be made from the study design description alone.

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 0% reporting threshold.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: stroke (4.8%).

The registry lists a serious adverse event figure of 1 among 21 at risk for the group titled GoodBelly Probiotic and Vancomycin. It lists 0 other adverse events among 21 at risk. The record’s serious-event term listing includes Stroke at 4.8%. These are registry safety entries; the information does not describe event timing, severity details, relatedness to an intervention, or how events were adjudicated.

The group title should be read alongside the sequential and partly optional intervention description. It does not establish that every participant received both probiotic and vancomycin, nor does it identify which treatment period was associated with an event. The record does not report an event-by-period breakdown or a comparison group, so the listed figures cannot establish whether an intervention caused an event or whether the observed frequency differs from another treatment or background risk.

Deaths are recorded as null, so death information is not reported in the registry record. The figures should not be interpreted as a complete safety profile: they describe the posted adverse-event entries, without detailed definitions, follow-up context, or a causal assessment. They also do not allow conclusions about risks outside the recorded group or about events not listed in the registry.

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

The registry record establishes that a completed study examined probiotic supplementation and endothelial function in men with coronary artery disease. It identifies brachial artery flow-mediated dilation as the primary outcome and describes measurement before and after 6 weeks of daily probiotic. It also documents a sequential study description involving a washout and optional vancomycin. These features clarify what the researchers set out to investigate.

The record does not include numerical primary-outcome results. It therefore cannot show the direction or size of any observed change, the variation among participants, or the precision of an estimate. It does not support a claim that probiotic supplementation improved, worsened, or had no effect on endothelial function. The same caution applies to secondary outcomes: their names are listed, but numerical results and analyses are not reported.

Even if a before-and-after change were available, the single-group design would make causal interpretation difficult. Changes over time can reflect the intervention, but can also reflect other factors or measurement variation. A randomized control group can help distinguish treatment effects from those alternatives; this registry record does not describe such a comparison. The absence of masking is another design feature relevant to interpretation, but it is not proof that measurements were biased.

The record also does not supply participant-level exposure, endpoint completion, missing-data handling, or analysis details. Therefore, the enrollment figure cannot be assumed to equal the number analyzed for the primary endpoint. The safety entries provide limited event information and do not establish that an intervention caused any listed event.

In practical statistical terms, the study record is informative about the question and measurement plan but insufficient for evaluating treatment effects. A reader would need posted outcome estimates, measures of uncertainty, and analysis details to judge the size and precision of the observed data. A completed status means the study is recorded as completed; it does not itself indicate what the results were or how conclusive they are.

14. Why This Trial Matters Statistically

This study is statistically instructive because its stated clinical question and primary measurement are identifiable, while the registry record does not report the outcome estimates needed to answer that question. A named endpoint and a defined measurement period do not, by themselves, reveal whether measurements changed or how precisely a change was estimated. Separating study aims from observed results is essential when reading trial records.

The design also illustrates why the comparator matters. A single-group before-and-after structure can describe change over time, but it cannot by itself distinguish an intervention-related change from other influences. The registry’s allocation and masking descriptions help readers identify this limitation rather than treating the study as a randomized treatment comparison. The sequential, partly optional antibiotic period adds a further reason to be precise about which intervention and timepoint a result would represent.

The record’s safety entries also demonstrate the importance of context. Counts and percentages without detail on timing, exposure, event definitions, or a control group do not establish causation or comparative risk. Likewise, an enrollment figure is not necessarily the analyzed sample for each outcome; participant flow and missing-data information are needed to understand the basis of estimates.

Finally, planning illustrations and trial results answer different questions. Hypothetical sample-size calculations depend on assumptions about a target effect and design. They are not observed power and do not replace the actual effect estimate or its uncertainty. This distinction is particularly important when planning assumptions describe a two-arm comparison but the recorded study itself is single group. The statistical lesson is to interpret each result in light of the design and to distinguish clearly between reported evidence, missing information, and general methodological principles.

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 main limitation for interpreting this specific study record is the absence of numerical outcome results. Although the primary endpoint and timeframe are described, the registry record does not report the observed brachial artery flow-mediated dilation values, an estimate of change, or its uncertainty. Numerical findings for the listed secondary outcomes are also not reported. The record lists no analyses, so statistical methods and results cannot be evaluated.

The single-group design provides no randomized concurrent comparator. Any before-and-after change, if reported elsewhere, would be difficult to attribute uniquely to probiotic supplementation. The registry also records no masking. It does not provide detail on measurement procedures beyond the endpoint description, assessor masking, or steps used to reduce measurement variability.

The intervention sequence is not fully characterized at the participant level. GoodBelly probiotic is followed in the description by a washout and optional vancomycin, but the record does not report who received the optional component, completion of each period, or the analysis of measurements related to each period. As a result, treatment exposure cannot be linked to individual outcomes from the registry information.

Other important details are not reported in the registry record: baseline participant characteristics, endpoint-specific numbers analyzed, reasons for missing observations, missing-data methods, analysis-population definitions, and the statistical analysis plan. The record does not report a sample-size justification or interim analyses. These gaps limit assessment of selection, precision, attrition, and analytic choices. The adverse-event entries likewise lack timing and causal attribution, and the null death entry does not provide a reported death result.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Effect of Probiotic Supplementation on Endothelial Function — NCT01952834.
• Registry record last updated 2016-01-21; status last verified 2015-12.
• Results first posted 2016-01-21.
• 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

NCT01952834 is recorded as a completed phase 4, single-group study sponsored by the Medical College of Wisconsin. It enrolled 21 men with coronary artery disease, with study dates recorded as 2013-06 to primary completion in 2015-03. Allocation is listed as NA and masking as none.

The primary endpoint was brachial artery flow-mediated dilation, described as percent change before and after 6 weeks of daily GoodBelly probiotic. The intervention description includes a 4 week washout and an optional vancomycin period lasting 10 days. Interleukin 8 and Interleukin-12 are listed as secondary outcomes.

Numerical primary and secondary outcome results, endpoint-specific analysis counts, and analysis methods are not reported in the registry record. The record lists one serious adverse event among 21 at risk, zero other adverse events among 21 at risk, and Stroke at 4.8% among the serious-event terms. It does not report death information.