A Study to Assess the Efficacy and Safety of the Vibrant Capsule Administered 5 Times Per Week: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study to Assess the Efficacy and Safety of the Vibrant Capsule Administered 5 Times Per Week (NCT03031301), a randomized na study. The primary outcome is CSBM1- Number of Participants With an Increase of at Least One Weekly Complete Spontaneous Bowel Movement (CSBM) During at Least 6 of the 8 Weeks of Treatment.

2. Clinical Question

The registry identifies constipation as the condition and describes the study as an evaluation of efficacy and safety. The primary endpoint is a participant-level success measure: each participant either met the stated increase criterion or did not. It is not a comparison of the average number of bowel movements, nor does the posted primary result describe the size of each participant’s change.

The statistical comparison contrasts the proportion meeting this criterion in the Vibrant Capsule arm with the proportion in the Sham Capsule arm. The registry’s arm results report 24 participants meeting the endpoint among 89 in the Vibrant Capsule arm and 33 among 93 in the Sham Capsule arm. The unadjusted risk difference is reported as -0.085, with a confidence interval from -0.219 to 0.049. These results describe the observed endpoint counts and the precision of an unadjusted comparison; they do not, on their own, establish why the groups differed or determine whether the device should be used.

3. Trial Design

The registry describes a prospective, multicenter, randomized, double-blind, sham-controlled study. Its official title also describes quadruple masking and a parallel design. The brief summary calls the study adaptive, but the registry record does not report the details of any adaptation, so its implementation cannot be characterized from the posted information.

The study compared Vibrant Capsule with Sham Capsule. The sham is described as activated but non-vibrating. Both treatments were administered 5 times per week for 8 weeks of treatment. The registry reports enrollment of 182 and lists the trial status as completed. It records a start date of 2017-02-01 and a primary completion date of 2018-07-30. Phase is recorded as NA.

The posted primary outcome concerns whether participants experienced an increase from the run-in period of at least 1 weekly complete spontaneous bowel movement during at least 6 of the 8 weeks of treatment. The arm-level result lists 89 participants for Vibrant Capsule and 93 for Sham Capsule. Those are the denominators attached to the posted arm outcomes; the registry record does not explain participant flow, exclusions, or how missing endpoint observations were handled.

Randomization is intended to support a comparison between groups, while masking and a sham comparator can help limit differences in expectations and assessment. These are general design principles, not evidence that bias was eliminated in this study. Details such as the randomization procedure, who was masked, and how the masking was maintained are not reported in the registry record. The record does not report the original statistical design assumptions or sample-size justification.

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 CSBM1- Number of Participants With an Increase of at Least One Weekly Complete Spontaneous Bowel Movement (CSBM) During at Least 6 of the 8 Weeks of Treatment, measured over 8 weeks.

The primary endpoint is a binary participant-level measure of CSBM1 success. Success is defined as an increase from the run-in period of at least 1 weekly complete spontaneous bowel movement during at least 6 of the 8 weeks of treatment. The result therefore counts participants who met the full criterion; it does not report the average change in bowel movement frequency or the amount of change beyond the threshold.

A complete spontaneous bowel movement combines two features: the movement is complete, and it occurs spontaneously. In general, a threshold-based endpoint can make a clinical outcome easier to interpret by specifying what qualifies as success in advance. Requiring the increase to occur during at least 6 of the 8 treatment weeks also makes the definition depend on a pattern across treatment, rather than a single week. These are general explanations of the endpoint’s structure, not claims about how it was chosen for this study.

The endpoint uses the run-in period as its reference, so success depends on a participant’s treatment-period experience relative to that baseline period. The registry record does not report further details about the run-in period, including its duration or the rules for collecting those measurements. It also does not report the rationale for choosing the threshold, the threshold’s validation, or additional endpoint definitions beyond the posted description.

The registry reports counts of participants meeting the criterion in each arm. Because the measure is binary, the comparison is about the proportion meeting the definition, rather than a direct comparison of continuous outcome values. The posted results do not establish whether other symptoms or outcomes changed in a similar way.

7. Results Posted in the Registry

• Vibrant Capsule: 27.0% (24/89) versus 35.5% (33/93) on control; risk difference -8.5 percentage points (95% CI -21.9 to 4.9), risk ratio 0.76 (0.49–1.18); unadjusted two-proportion z-test p = 0.216.

8. Statistical Interpretation

9. Statistical Methods Explained

What does a binary endpoint mean?

A binary endpoint places each participant into one of two categories: the defined success criterion was met, or it was not. Here, the registry reports the number meeting the CSBM1 criterion and the number of participants in each arm. This format is useful when the research question is whether participants reach a specified threshold. It does not preserve all the detail in the underlying bowel movement measurements, such as how far a participant’s change was above or below the threshold.

For a binary outcome, the arm-level proportion is the count meeting the criterion considered relative to the number in that arm. The posted statistical comparison uses the arm counts and denominators. No new proportion needs to be calculated to interpret the reported risk difference, risk ratio, or odds ratio.

What does the risk difference express?

The risk difference compares the proportion meeting the endpoint in the Vibrant Capsule arm with the corresponding proportion in the Sham Capsule arm. Its sign indicates the direction of the contrast: a negative estimate means the observed proportion was lower in the Vibrant Capsule arm. The estimate is -0.085. Unlike a relative measure, a risk difference is on the absolute scale of the outcome proportions. The confidence interval gives a range of values compatible with the data and the method used to calculate it, subject to the method’s assumptions.

How do the risk ratio and odds ratio differ?

A risk ratio compares the outcome proportions as a ratio; a value corresponding to no relative difference is 1. The reported estimate is 0.76, and its interval is 0.490 to 1.178. An odds ratio compares odds rather than proportions; its no-difference value is also 1. The reported estimate is 0.671, with an interval of 0.357 to 1.263. Odds and probabilities are related but are not interchangeable, so an odds ratio should not be described as a risk difference. The intervals for both relative measures include their no-difference value.

What does the p-value tell the reader?

The unadjusted p-value is 0.216. In general, a p-value describes the compatibility of the observed data with a specified null model, assuming the analysis model and other relevant conditions apply. It is not the probability that the null hypothesis is true, and it is not a measure of the size or clinical importance of a difference. The registry record does not report the testing procedure or say whether this value was part of a prespecified analysis. The word “unadjusted” indicates that the comparison is not presented as adjusted for other variables or multiple testing.

The planning assumptions separately mention a two-sided significance level of 0.05. That value belongs to the planning illustration and should not be mistaken for a reported trial analysis threshold. The registry record does not report the trial’s own statistical analysis plan, its original significance level, or whether any interim analysis was conducted.

Why can over-dispersion matter?

Over-dispersion is a general concern in some statistical models when the observed variation exceeds what the model assumes. If a model underestimates variation, its standard errors may be too small and its confidence intervals too narrow. The posted primary endpoint is binary, and the registry record does not report a model that accounts for over-dispersion. Therefore, over-dispersion should not be asserted as a feature of this analysis. More generally, the choice of model and its assumptions matter because they affect uncertainty estimates and tests.

What is not available about the analysis?

The registry record reports arm counts and an unadjusted comparison, but it does not report a detailed statistical analysis plan, the calculation method for the confidence intervals, covariate adjustment, handling of missing endpoint data, or the analysis population. It also does not report whether the analysis followed an intention-to-treat, per-protocol, or other population definition. Such choices can affect the interpretation of a clinical-trial result. Without those details, the posted estimates can be described on their stated unadjusted basis, but their robustness to alternative analytic choices cannot be assessed from the registry record.

The registry lists no posted secondary outcomes in the results information and no sponsor analysis. This limits the ability to compare the primary endpoint with other reported efficacy measures or to evaluate a fuller analysis of the trial. General statistical explanations above clarify the meaning of the reported quantities; they do not fill in the analysis details that are not reported in the registry record.

10. Confidence Intervals and Precision

The confidence interval for the primary risk difference runs from -0.219 to 0.049, around an estimate of -0.085. It crosses zero, the value representing no difference on the risk-difference scale. Thus the interval does not isolate a direction of difference. Its lower end is compatible with a larger negative contrast, while its upper end is compatible with a positive contrast. This is uncertainty about the comparison, not evidence that all values in the interval are equally plausible.

The relative-measure intervals also include their no-difference value. The risk ratio is 0.76, with an interval from 0.490 to 1.178; the odds ratio is 0.671, with an interval from 0.357 to 1.263. Looking across these measures, the posted estimates do not tightly determine the direction or size of the group contrast.

A confidence interval is a statistical range constructed by a method that, under its assumptions, would capture the target parameter at the stated rate over repeated use. It is not a guarantee that the true value lies inside this particular interval, nor does it describe the range of individual participant outcomes. The registry record does not state the confidence level or calculation method in the posted primary comparison, so those details should not be assumed from the displayed endpoints alone.

Precision depends on the amount and pattern of information in the data, as well as the analysis method. The arm denominators are 89 and 93, and the reported interval is broad enough to include differences in either direction. The posted result therefore supports a cautious reading: it estimates a negative unadjusted contrast, but leaves substantial uncertainty about its magnitude and direction.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total events. They are illustrations computed from the observed effect under the listed planning assumptions, rather than the original trial design calculation. The assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each scenario uses the stated fraction of the observed effect as the effect to detect.

The 80% power column gives the illustrative number of participants per arm for a design intended to have an 80% chance of detecting the chosen effect under those assumptions, if that effect and the model assumptions were correct. The 90% power column expresses the same planning idea with a higher target chance of detection. These values are not results from the completed trial. This is not observed power.

For planning at 100% of the observed effect, the illustration lists 464 participants per arm for 80% power and 620 participants per arm for 90% power. For planning at 75% of the observed effect, it lists 840 participants per arm for 80% power and 1,124 participants per arm for 90% power. For planning at 50% of the observed effect, it lists 1,923 participants per arm for 80% power and 2,574 participants per arm for 90% power. The plotted curve is a visual representation of the same planning relationship, not additional evidence about what happened in the trial.

Smaller effects are harder to distinguish from random variation, so detecting smaller effects generally requires more participants. The figures do not establish the sample size that the trial originally intended to enroll. The original design assumptions and sample-size justification are not reported in the registry record.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.355; treatment proportion p₁ = 0.270; average p̄ = 0.312.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.6554 = 1.2845.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.6526 = 0.5492.
4. n = (1.2845 + 0.5492)² / (-0.0852)² = 463.5, rounded up to 464 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
p0 <- 0.354838709677419                          # control proportion
p1 <- 0.269662921348315                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(3031301)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 464 (80% power), 620 (90% power)
 75% of observed effect: n per arm = 840 (80% power), 1,124 (90% power)
 50% of observed effect: n per arm = 1,923 (80% power), 2,574 (90% power)
power.prop.test: 463.5 
Simulated power at n = 464 per arm: 0.805 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Multiplicity, Missing Data and Analysis Populations

The registry record lists the primary CSBM1 outcome and reports no posted secondary outcomes in the results information. It does not report a multiplicity plan describing how the statistical interpretation would account for testing more than one endpoint, time point, subgroup, or analysis. Without such a plan, the role of the unadjusted p-value in a broader family of tests is not reported in the registry record. This is relevant because repeated testing can increase the chance of finding a nominally unusual result by chance.

Missing-data handling is also not reported in the registry record. The posted arm denominators are 89 for Vibrant Capsule and 93 for Sham Capsule, but the record does not explain whether all randomized participants contributed an evaluable primary outcome, how incomplete weekly information was treated, or whether any values were imputed. The endpoint depends on meeting a criterion across at least 6 of the 8 treatment weeks, so the handling of incomplete observations could matter to classification; the record does not provide enough detail to assess that issue.

The analysis population is not reported in the registry record. The posted results do not state whether the analysis used all randomized participants, participants who began treatment, participants who completed treatment, or another defined group. Nor is there information about protocol deviations or exclusions from the primary analysis. These details are important for understanding whether the comparison preserves the intended randomized groups.

The registry record does not report interim analyses, stopping rules, or the trial’s statistical analysis plan. It also does not report whether any covariate adjustment or sensitivity analyses were performed. These omissions limit assessment of prespecification and robustness, but they do not change the values in the posted unadjusted comparison. They mean that the reported endpoint counts and estimates should be interpreted with the analytic details left unresolved.

14. 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 1% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: traumatic fracture of pelvis (1.1%), anxiety attack (1.1%).

The registry reports serious adverse events for 1 participant in the Vibrant Capsule arm, among 89 at risk, and 1 participant in the Sham Capsule arm, among 93 at risk. Deaths are reported as 0 in each arm. These are counts recorded in the registry; they do not by themselves establish whether an event was caused by a study capsule.

The registry also lists 28 participants with other adverse events in the Vibrant Capsule arm and 19 in the Sham Capsule arm. The posted summary does not provide enough detail to interpret severity, timing, duration, or causal attribution for those other events. The serious-event terms listed are “Traumatic Fracture Of Pelvis” and “Anxiety Attack,” each reported as 1.1%. The record does not specify a group attribution for those terms in the information summarized.

Adverse-event counts provide safety context but should not be treated as a complete account of risk. The registry record does not report event-level narratives or the methods used to collect and classify the events. Counts from this study do not establish that an event was caused by treatment or that an unlisted event did not occur.

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

The posted result answers a narrow question: how the two randomized groups compared on the registry’s stated binary CSBM1 success criterion. The Vibrant Capsule arm had 24 participants meeting the endpoint among 89, compared with 33 among 93 in the Sham Capsule arm. The unadjusted risk difference was -0.085, and its confidence interval extended from -0.219 to 0.049. The estimate favors the sham arm on this measure, but the interval includes zero and values in either direction.

The result does not establish that the Vibrant Capsule works or does not work. It does not demonstrate equivalence between the arms, because the registry does not report an equivalence design or a prespecified equivalence margin. It also does not establish that the groups are meaningfully different. The interval leaves uncertainty about the direction and magnitude of the comparison.

The primary endpoint is one defined threshold based on change from the run-in period. It does not describe every aspect of constipation, the distribution of individual responses, or the average number of complete spontaneous bowel movements. The registry record does not report additional secondary outcomes in the results information, so the posted primary result cannot be used to make claims about outcomes that are not reported.

Likewise, the safety counts are descriptive. They report serious adverse events and deaths by arm, but they do not establish causation or provide all the clinical context needed to characterize individual events. The study’s completed status and enrollment figure do not remove uncertainty in the posted outcome comparison. Overall, the registry data support a careful description of the observed counts and unadjusted estimates, while leaving the analysis population, missing-data approach, and fuller statistical plan unreported.

16. Why This Trial Matters Statistically

This trial illustrates why a clinical-trial result should be read through both the effect estimate and its uncertainty. The primary risk difference is negative, but the confidence interval crosses zero and spans values on either side. Looking only at the direction of the point estimate would overstate what the posted data can establish; looking only at the p-value would also omit the range of differences compatible with the analysis.

The binary success definition is another important statistical feature. It translates a repeated pattern of bowel movement measurements into a participant-level success count. That can make a result easier to communicate, but it also means participants with different underlying patterns can be placed in the same category. The threshold and timeframe therefore shape the question being answered. The record reports the definition, but not its rationale or the detail needed to evaluate alternative endpoint choices.

The sham-controlled, randomized design is relevant to how the groups were compared, while the missing analysis details limit assessment of how closely the posted result reflects the intended analysis. In particular, the registry record does not report how incomplete endpoint data were handled, which participants formed the analysis population, or how multiplicity was addressed. These are not merely reporting details: they can influence the interpretation of uncertainty and the scope of conclusions.

The sample-size illustrations also show why planning should be based on a plausible target effect rather than automatically treating an observed estimate as fixed. The posted planning values increase as the target effect becomes smaller. They are illustrations, not observed trial power or evidence that the completed study was designed around those assumptions. Taken together, these features make the study useful for understanding the statistical limits of a binary endpoint comparison, not for making a definitive claim from the point estimate alone.

17. 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.

Several trial-specific details needed to judge the result are not reported in the registry record. Although the brief summary calls the study adaptive, the record does not describe what was adapted, when adaptation could occur, or whether adaptation affected enrollment or analysis. It also does not provide the randomization method, the masking procedures, or an explanation of who was included under the quadruple-masking description. The design labels alone do not establish how these procedures operated in practice.

The registry describes treatment for 8 weeks and a success endpoint requiring the criterion during at least 6 of those weeks, but it does not report how missing weekly measurements were handled. It does not explain whether participants discontinued, were excluded, or had incomplete outcome data. The analysis population, protocol deviations, and reasons for any exclusions are also not reported. Consequently, the arm denominators and endpoint counts cannot be fully reconciled with participant flow from the registry information.

The trial’s original sample-size assumptions and statistical analysis plan are not reported in the registry record. The available sample-size values are planning illustrations based on the observed effect, not the trial’s own design justification. The registry also does not report any sponsor analysis, secondary outcome results, interim analyses, sensitivity analyses, or a multiplicity strategy. These omissions limit assessment of prespecification and robustness.

The primary outcome is a threshold-based measure, so it does not reveal the full distribution of individual changes. The registry record also provides limited detail about adverse events beyond counts and listed terms. These limitations do not invalidate the posted counts, but they restrict the conclusions that can be drawn from them.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: A Study to Assess the Efficacy and Safety of the Vibrant Capsule Administered 5 Times Per Week — NCT03031301.
• Registry record last updated 2024-07-03; status last verified 2019-01.
• Results first posted 2024-07-03.
• 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.

21. Record Summary

The registry record describes NCT03031301 as a completed, prospective, multicenter, randomized, double-blind, sham-controlled study, with quadruple masking and a parallel design also recorded. It lists constipation as the condition, enrollment of 182, and phase as NA. The recorded start date is 2017-02-01, and the primary completion date is 2018-07-30.

The study compared Vibrant Capsule with an activated, non-vibrating Sham Capsule, each administered 5 times per week for 8 weeks. The primary endpoint was the number of participants with an increase from the run-in period of at least 1 weekly CSBM during at least 6 of the 8 treatment weeks.

The posted primary counts were 24 among 89 for Vibrant Capsule and 33 among 93 for Sham Capsule. The unadjusted risk difference was -0.085, with a confidence interval from -0.219 to 0.049 and an unadjusted p-value of 0.216. The registry reports 1 serious adverse event in each arm and 0 deaths in each arm. Details of the analysis plan, missing-data handling, and analysis population are not reported in the registry record.