BlueWind RENOVA iStim™ System for the Treatment of OAB: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for BlueWind RENOVA iStim™ System for the Treatment of OAB (NCT03596671), a na na study. The primary outcome is ≥50% Decrease in Mean Urinary Urgency Incontinence (UUI) Episodes.

2. Clinical Question

This is a question about the frequency of a prespecified type of response within the treated group. It is not a direct estimate of how outcomes compare with an untreated group or another intervention. Without a reported endpoint result, the registry record cannot establish how common the defined response was among participants assessed at 6 months. It also does not report how many participants contributed data to that endpoint, how missing diary data were handled, or the characteristics of participants included in the analysis.

3. Trial Design

OASIS is described as a prospective, interventional, multicenter study assessing the safety and efficacy of the RENOVA iStim™ System in patients diagnosed with overactive bladder. The registry lists the study as single-group, with a treatment arm of implanted patients. Allocation is recorded as NA, and masking is listed as none. The study is marked completed. Its phase is recorded as NA.

The registry lists enrollment as 282. This is the recorded enrollment figure; it does not establish how many participants were included in each outcome analysis or completed follow-up. The safety fields separately list 151 at risk for serious adverse events and 151 at risk for other adverse events. Those safety denominators should not be treated as a complete account of the endpoint population or reconciled with enrollment without further information.

The recorded start date is 2019-06-12, and the primary completion date is 2022-10-28. The intervention is the RENOVA iStim™ System, categorized as a device. The registry's brief description calls it an implantable tibial neuromodulation system. Details such as recruitment procedures, eligibility criteria, treatment delivery, follow-up schedules beyond the primary endpoint timeframe, and study-site locations are not reported in the registry record.

Because the design has a single treatment group, the study can describe outcomes observed among participants who received the system, if those outcomes are reported. It cannot, on its own, separate changes associated with treatment from changes that might have occurred over time, measurement variability, or other influences. The registry record does not report a control group or a randomized allocation process.

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

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 ≥50% Decrease in Mean Urinary Urgency Incontinence (UUI) Episodes, measured over 6 months.

The primary endpoint is the percentage of responders at 6 months after system activation. A responder is defined as having at least a 50% improvement in the average number of urgency-related urinary incontinence episodes. Episode frequency is measured using a 7-day Patient Voiding Diary. The registry identifies the outcome as a proportion and lists a 95% confidence interval as its dispersion measure.

This endpoint turns diary-recorded episode frequency into a binary classification: each assessed participant either meets the stated response threshold or does not. A proportion is useful for expressing how common a defined level of improvement was in the assessed group. The diary provides a specified observation window for recording episodes, while the threshold gives a common rule for classifying response.

As a general statistical point, converting a continuous or count-based measure into a responder outcome can make the result easier to interpret as the share of participants reaching a chosen benchmark. It also discards information about the amount of change within each category: people just below the threshold and those with no improvement are both nonresponders under this definition, while people with different amounts of improvement above the threshold are all responders. The registry record does not report the observed responder percentage, the confidence interval limits, the analysis population, or the handling of unavailable diaries.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry record describes a binary responder endpoint and identifies a 95% confidence interval as its dispersion measure. It does not report the responder estimate, interval limits, analysis method, or analysis population. The explanations below describe general statistical ideas; they are not claims about methods actually used in OASIS.

What does a responder percentage represent?

For a binary endpoint, each participant with an evaluable outcome is classified according to whether the stated criterion was met. The responder percentage expresses the share of those assessed participants who met that criterion. In this study, the criterion is at least a 50% decrease in mean urinary urgency incontinence episodes, measured using a 7-day Patient Voiding Diary, at 6 months after system activation.

The denominator is essential to interpreting a percentage. It should be clear which participants were considered eligible for the analysis and which had the outcome measured. Enrollment alone does not reveal that denominator: some enrolled participants may not have an assessment at the endpoint, and the record does not state how such cases were handled. The analyzed denominator and the number meeting the threshold are not reported in the registry record.

What does a confidence interval add?

As a general explanation, a confidence interval conveys uncertainty around an estimated quantity. For a responder percentage, it gives a range of values compatible with the observed data under the interval procedure's assumptions. It does not list the range of outcomes among individual participants, and it is not a guarantee that the true value lies inside the interval. Its width depends in part on the amount of information available and on the method used.

The registry names a 95% confidence interval for the primary endpoint but does not provide its limits. It is therefore not possible to evaluate how precise the responder estimate was. The interval method is also not reported in the registry record. Different methods can behave differently, particularly when the amount of information is limited or the estimated proportion is near a boundary.

Why does the single-group structure matter?

In general, a single-group study estimates outcomes in the group observed, rather than estimating a contrast between groups. A treated-group response proportion can describe how many assessed participants met a threshold, but it does not by itself show what would have happened to those participants without the intervention. Randomization and a suitable comparator can help make a between-group contrast more interpretable, but the registry describes no such comparison.

This design issue is separate from sampling uncertainty. A confidence interval can quantify uncertainty around a group estimate under a statistical model, but it cannot remove the limitations of not having a concurrent comparison group. Precision about a treated-group proportion is not the same as precision about a causal treatment effect.

What can be said about planning calculations?

The study's own sample-size justification is not reported in the registry record. A planning illustration, if considered, is not evidence of the study's original design rationale and is not observed power. The described illustration uses a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is a stated fraction of the observed effect. It is explicitly a planning calculation based on the observed effect, not a report of a randomized design in OASIS. The registry describes OASIS as single-group, so the assumptions for a two-arm illustration do not describe the study's recorded structure.

In general, planning calculations depend on a target effect, a variability model, a significance criterion, and a desired probability of detecting the target effect under assumed conditions. They answer a prospective design question. They do not establish that a study had adequate power for an outcome, and they do not change the uncertainty in an observed result. The target effect fractions used for any such illustration and the resulting participant estimates are not stated in the registry record.

Why can over-dispersion matter?

As a general concept, over-dispersion occurs when observed variability is greater than a statistical model assumes. For count outcomes, such as episodes recorded in a diary, a model that underestimates variation can produce standard errors that are too small and confidence intervals that are too narrow. Methods that account for extra variation may therefore be important in some analyses of counts. The registry record does not report a count model, a dispersion estimate, or whether any adjustment for over-dispersion was used.

The primary endpoint is described as a responder proportion, rather than as a modeled count of episodes. That classification does not reveal how the diary measurements were summarized, how the average was calculated, or how uncertainty was estimated. Those methodological details are not reported in the registry record.

What is not documented about the analysis?

The registry lists two outcome measures and zero analyses. It does not identify an analysis population, a statistical model, covariate adjustment, an interim analysis, or a protocol-based sample-size rationale. The absence of a listed analysis is not evidence that no analysis was done; it means that analysis results and methods are not documented in this registry record. Consequently, the endpoint definition can be explained, but the estimate, precision, and analytic assumptions cannot be independently evaluated from the record.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Treatment Arm")
n      <- c(151)
events <- c(115)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Treatment Arm  151  115  76.2  68.6  82.7  68.8  82.3  68.7  82.2

11. Multiplicity, Missing Data and Analysis Populations

The registry lists two outcome measures and zero analyses, but it does not report a multiplicity strategy. Multiplicity arises when several outcomes, time points, subgroups, or statistical tests are evaluated: the chance of at least one apparently notable finding can increase as the number of tests grows. General approaches include defining one primary test in advance or adjusting interpretation for multiple comparisons. The registry record does not state whether such procedures were planned or used, and the two listed outcome measures alone do not establish how many analyses were performed.

The primary endpoint is specified at 6 months after system activation. Other analysis time points, interim looks at accumulating results, or subgroup comparisons are not reported in the registry record. The record also does not report whether the primary endpoint definition changed or whether any protocol deviations affected its analysis.

Missing data are particularly relevant to a responder proportion because the classification depends on having usable diary information. The record does not say how many participants had a diary assessment at the endpoint, how unavailable or incomplete diaries were handled, or whether participants without endpoint data were counted as nonresponders, excluded, or addressed through another method. These choices can alter both the estimated proportion and its uncertainty.

The analysis population is not reported in the registry record. It is therefore unclear whether the endpoint was evaluated among all enrolled participants, those who received the intervention, those with follow-up data, or another defined group. The enrollment figure should not be assumed to be the primary endpoint denominator. No missing-data assumptions, sensitivity analyses, or analysis-population definitions are documented in the record.

12. 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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: covid-19 (0.7%), cellulitis (0.7%), herpes zoster meningitis (0.7%), pneumonia (0.7%), postoperative wound infection (0.7%).

The treatment-arm safety fields list 151 at risk for serious adverse events and 13 affected, alongside 151 at risk for other adverse events and 34 affected. Deaths are listed as 0. These are registry counts, and the record does not provide further information about the definitions used for the affected counts, event timing, severity criteria, or attribution to the device or procedure. The at-risk denominators are safety fields and should not be assumed to be the primary endpoint analysis population.

The serious adverse-event terms listed are COVID-19, cellulitis, herpes zoster meningitis, pneumonia, postoperative wound infection, and sinusitis, each with a recorded value of 0.7%. These term-level entries should be read as descriptive listings, not as evidence that the device caused the events. The record does not explain whether a participant could be represented by more than one term or how the term-level percentages were calculated.

Safety counts without a comparator do not establish whether event frequency differs from another treatment or from background occurrence. They also do not, on their own, establish causation. The registry record does not report additional detail needed to interpret individual events or to compare risks between groups.

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

The record documents a prospective, interventional, multicenter, single-group study of the RENOVA iStim™ System in patients diagnosed with overactive bladder. It defines a primary outcome based on a threshold reduction in urinary urgency incontinence episodes, assessed at 6 months after activation using a 7-day Patient Voiding Diary. This information clarifies what the study intended to measure and the design in which it was assessed.

The registry record does not report the primary responder percentage or its 95% confidence interval. It therefore does not show how often participants met the endpoint or how precise that estimate was. The endpoint description must not be mistaken for an observed result. The record also does not report an analysis population, missing-data approach, or statistical model for the primary outcome.

Even if the treated-group endpoint estimate were reported, the single-group design would describe outcomes among participants observed in that group rather than estimate a comparison against a control. Without a separate comparator, differences between observed outcomes and what might otherwise have occurred cannot be isolated using this design alone. This limitation concerns causal interpretation and is not resolved by having a defined endpoint or a confidence interval.

The safety information is also descriptive. The record lists serious and other adverse-event counts, serious-event terms, and a death count, but does not provide details sufficient to establish causation or compare risks with another group. The counts should be interpreted within the limitations of the recorded denominators and the missing definitions.

Accordingly, the registry entry is informative about study structure, the intended primary endpoint, and selected safety reporting. It does not provide the numerical efficacy result needed to describe the observed response rate, nor does it support a comparative estimate of treatment effect. Further outcome and methods information is not reported in the registry record.

14. Why This Trial Matters Statistically

This study raises several statistical issues that are important when interpreting device studies in a single group. First, a clearly defined responder threshold can make an outcome understandable, but interpretation still requires the observed proportion, its uncertainty, and the denominator on which it is based. The registry specifies the response rule and timeframe, yet does not report the estimate, confidence interval limits, or endpoint analysis population.

Second, the design determines the question the data can answer. A single-group study can characterize observed outcomes in treated participants, but it does not offer a concurrent comparison that separates treatment-associated change from other explanations. This distinction remains important even when an outcome is measured prospectively and using a defined diary period.

Third, diary-based endpoints depend on the completeness and handling of repeated symptom records. The registry does not report how incomplete diaries or missing endpoint assessments were treated. Transparent reporting of these decisions helps readers understand who contributed to an estimate and whether the results may depend on assumptions about missing observations.

Finally, safety reporting requires careful separation of affected counts, event terms, and denominators. The registry lists serious and other adverse-event fields, but provides limited interpretive detail. Reading these figures as descriptive rather than comparative avoids attributing causation or making unsupported comparisons. Together, these points show why design, endpoint definition, analysis details, and complete result reporting are all necessary for a statistical assessment.

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 primary limitation for interpreting efficacy is that the registry record does not report the primary endpoint result or its confidence interval, even though it defines the endpoint and names the interval measure. The number of participants contributing to the endpoint analysis is also not reported. The enrollment figure cannot substitute for an endpoint denominator without information about follow-up and analysis inclusion.

The single-group design has no recorded comparator arm and no randomized allocation. Consequently, the study structure does not provide a direct between-group estimate of treatment effect. The registry record also does not report masking beyond listing none, or details that would allow assessment of how outcome assessment and diary recording were conducted.

Further limitations arise from missing methodological information. The record does not report the primary analysis method, analysis population, missing-data handling, sample-size justification, interim analyses, multiplicity procedures, or protocol deviations. It lists zero analyses, which indicates that analysis results are not present in the registry record but does not establish what was done outside it.

For safety, the record includes risk denominators and affected counts, but does not state event definitions, attribution, timing, or whether the listed serious-event terms may include repeated events or participants. The term-level percentages are reported, but the method for calculating them is not described. These omissions limit interpretation of the safety fields and prevent meaningful comparative conclusions.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: BlueWind RENOVA iStim™ System for the Treatment of OAB — NCT03596671.
• Registry record last updated 2025-09-16; status last verified 2025-08.
• Results first posted 2025-09-16.
• 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

OASIS is a completed, prospective, interventional, multicenter, single-group study of the RENOVA iStim™ System for patients diagnosed with overactive bladder. The registry records enrollment as 282, allocation as NA, masking as none, and phase as NA. The recorded study start date is 2019-06-12, and the primary completion date is 2022-10-28.

The primary endpoint is the percentage of responders at 6 months after system activation, defined by at least a 50% decrease in mean urinary urgency incontinence episodes measured using a 7-day Patient Voiding Diary. The registry record does not report the endpoint result, confidence interval limits, analysis population, or missing-data methods. Safety fields list serious and other adverse-event counts and deaths as 0; event attribution and further definitions are not reported in the registry record.