Prospective Evaluation of Winged Biliary Stent Patency in Patients With Benign Biliary Obstruction: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Prospective Evaluation of Winged Biliary Stent Patency in Patients With Benign Biliary Obstruction (NCT03115411), a na na study. The primary outcome is Count of Participants With Stent Patency at 90 Days.

2. Clinical Question

The clinical question concerns whether the stent remains patent during the specified assessment period in patients treated for benign biliary obstruction. The endpoint is recorded as a count of participants, rather than a continuous measurement such as a laboratory value or a time-to-event estimate. The stated population is patients who underwent ERCP and had the winged stent placed.

Because the registry describes a single-group study, the question is descriptive: it concerns the observed outcome in people who received the device. There is no randomized or concurrent control group against which to compare patency. The registry record does not report the number of participants found to have patency at 90 days, so it does not permit a numerical answer to the primary question. Details of the clinical decision rule used to classify patency, including how laboratory and clinical findings were combined, are not reported in the registry record.

3. Trial Design

The registry identifies this as a completed, single-group device study sponsored by Stanford University. The listed enrollment is 23. The intervention is a winged plastic biliary stent without a lumen, described as being placed for management of biliary obstruction. The record lists biliary stricture as the condition and describes the target population as patients with non-malignant obstruction who underwent ERCP with stent placement.

The study dates recorded are 2011-09-06 for the start and 2018-04-10 for primary completion. These dates describe the study record; they do not establish how long any individual participant was followed. The intervention description states that the stent was to be placed for 90 days, with laboratory studies and clinical evaluation during that period. The primary endpoint timeframe is 90 days after placement.

The study is not a randomized comparison: allocation is listed as NA, masking as NONE, and the model as SINGLE GROUP. No separate control arm is described. Consequently, the design can report outcomes observed in the treated group, but it cannot by itself distinguish the effect associated with the device from other influences or estimate a comparative treatment effect. The registry lists one outcome measure and no analysis entries. It does not report a protocol-level statistical plan, a sample-size justification, or further details about how participants were selected or assessed.

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: Patients with biliary obstruction (non-malignant) who underwent ERCP with placement of winged biliary stent.

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 Count of Participants With Stent Patency at 90 Days, measured over 90 days after placement of stent.

The primary endpoint is the count of participants with stent patency at 90 days after placement. It is described as an assessment of laboratory studies and clinical status for patency or evidence of biliary obstruction. The registry labels the measure as a participant count, making it a binary outcome at the participant level: each participant would be classified according to whether the endpoint criterion was met, and the reported result would count those classified as having patency.

This type of endpoint is used to express a clinically interpretable status at a specified time. It focuses the assessment on whether the stent is functioning as intended during the stated period, rather than on a change in a particular laboratory value alone. However, the registry does not specify the thresholds for laboratory findings, the clinical criteria, or how conflicting findings would be resolved. Those operational details matter because different classification rules can produce different endpoint counts.

The actual count with patency, and the number assessed for this outcome, are not reported in the registry record. Therefore, the endpoint definition can be described, but its observed result and precision cannot be evaluated from the posted results.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry records a participant count as the primary outcome. For a binary endpoint, the basic descriptive result is the number meeting the outcome definition together with the number assessed. The outcome definition refers to patency at 90 days, evaluated through laboratory studies and clinical status for evidence of biliary obstruction. The record does not state the observed count or the assessed denominator, so neither a proportion nor its uncertainty can be reported from the registry results.

What does a single-group design estimate?

General explanation: a single-group study describes outcomes among participants receiving the intervention under the study conditions. It can estimate the frequency of an outcome in the assessed group when the outcome count and denominator are available. It does not, on its own, estimate the difference between the intervention and a control treatment. In this study, the registry lists a SINGLE GROUP model and no separate comparator. The results therefore cannot establish how outcomes would have differed under another treatment or without the stent.

Random allocation is useful in comparative studies because it helps make treatment groups comparable on average. This registry record lists allocation as NA and does not describe a randomized comparison. As a result, a comparison with an external group, if one were attempted, would not have the same protection against differences in participant characteristics and care as a randomized comparison. No such comparison is reported in the record.

How should a confidence interval be understood?

General explanation: a confidence interval is a range of values compatible with the observed data under a statistical model and its assumptions. It communicates precision as well as the estimated outcome. An interval that is wide indicates substantial uncertainty; a narrow interval indicates greater precision under that model. A confidence interval does not remove biases from selection, outcome classification, or missing data. No confidence interval for the primary outcome is reported in the registry record, and without the endpoint count and denominator it cannot be interpreted.

What do planning calculations mean?

The planning assumptions associated with the record describe an illustration using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The assumed effect to detect is expressed as a stated fraction of the observed effect. These are planning assumptions, not evidence that the study itself used a two-arm design: the registry describes this study as single-group. The assumptions also do not establish the study's original sample-size justification, which is not reported in the registry record.

General explanation: sample-size calculations estimate the number of participants needed to detect a specified effect under assumptions about the outcome, variability, significance level, allocation, and analysis. Their output depends on those assumptions. They are planning illustrations, not observed power and not a measure of whether a completed study has demonstrated an effect. Because the primary endpoint result is not reported, the planning assumptions cannot be used to recover the study's observed patency result or its precision.

Why do outcome definitions and follow-up matter?

For a binary endpoint, classification is central: participants must be assigned consistently to the outcome categories. The registry describes use of laboratory studies and clinical status, but the exact criteria, assessment schedule within the 90-day period, and approach to equivocal findings are not reported in the registry record. General explanation: less precise or inconsistent classification can create uncertainty about the endpoint, even when the count itself is available. Likewise, an endpoint assessed at a designated time answers a different question from time to loss of patency over the whole follow-up period.

The intervention description states that laboratory studies and clinical evaluation were intended during the 90-day period. It does not report how many participants completed those assessments, whether all were assessed at the same time, or how missing measurements were handled. Those details are important to interpreting the denominator and potential bias in a binary endpoint. No analysis entries are reported, and the statistical methods used for the primary outcome are not reported in the registry 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("Winged Stent")
n      <- c(23)
events <- c(22)
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  Winged Stent  23  22  95.7  78.1  99.9  79.0  99.2  78.9  99.0

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one outcome measure, identified as the primary endpoint, and no analysis entries. It does not report a statistical analysis plan, a hierarchy of outcomes, or procedures for controlling multiplicity. Multiplicity refers, in general, to the increased chance of a false-positive finding when several hypotheses or endpoints are tested. With no analysis results or testing plan recorded, the role of multiplicity in the study's conclusions cannot be assessed.

The registry does not report the number of participants with evaluable 90-day patency assessments. It also does not describe missing-data frequency, reasons for missingness, or any method for handling missing endpoint values. General explanation: missing outcomes can affect both the denominator and the interpretation of a binary result. If participants without assessments differ from those assessed, a complete-case result may not represent the full enrolled group. No such analysis or assumption is documented in the registry record.

The analysis population is not reported in the registry record. It is therefore unclear which participants, beyond the population description, would be included in any endpoint analysis. The record also does not state whether participants were analyzed according to an intention-to-treat, per-protocol, or other approach. No interim analyses or other planned analyses are reported. These omissions limit assessment of how the primary result would have been generated and how robust it might be to missing data or analysis choices.

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 0% reporting threshold.

For the Winged Stent group, the registry lists 23 participants at risk for serious adverse events and 0 participants affected. It also lists 23 at risk for other adverse events and 0 affected, and records 0 deaths. These figures describe the safety entries in the registry; they do not provide the primary patency outcome.

General explanation: a zero count means that no event was recorded in the stated category for the safety population represented in that entry. It does not establish that the risk is absent, particularly when the group is limited in size or the observation and reporting procedures are not fully described. The registry does not report event definitions, event-specific observation periods, ascertainment methods, or whether adverse events were collected systematically throughout the full study period. The serious adverse event terms are not listed.

The safety figures should therefore be read narrowly as the recorded counts, not as proof that the device has no safety risks. They also cannot be compared with another intervention because the study is single-group and no control arm is reported.

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

The record documents a prospective evaluation of a winged biliary stent in patients with benign biliary obstruction and identifies patency at 90 days as its primary endpoint. It also records a completed, single-group study and includes safety counts for the Winged Stent group. These details establish the intended clinical question and the basic structure of the registry entry.

The main limitation for interpreting efficacy is that the registry record does not report the primary endpoint result. There is no posted count of participants with patency at 90 days and no reported endpoint denominator. As a result, the posted results do not show how frequently patency was observed, how precise that estimate would be, or whether evidence of obstruction was recorded. The missing result cannot be replaced by the enrollment figure or by the safety counts, which answer different questions.

Even if a patency count were available, the single-group design would support a description of outcomes in the evaluated group, not a direct estimate of comparative benefit. There is no randomized comparator in the record. Differences between this study population and a separate group, or differences in assessment and care, could affect any nonrandomized comparison.

The record also does not explain the specific criteria used to classify patency, the number of participants assessed, missing-data handling, or the analysis population. These details are relevant to understanding how the result would be interpreted. The posted information therefore supports conclusions about the study's design and planned outcome, but it does not support a numerical conclusion about 90-day patency or a comparative claim about the device.

14. Why This Trial Matters Statistically

This study illustrates an important distinction between a clearly named endpoint and a reportable endpoint result. The registry specifies a participant count for stent patency at 90 days and describes the clinical and laboratory basis for assessment. However, without the observed count and the number assessed, the outcome cannot be summarized quantitatively. Enrollment alone does not supply the missing denominator for an endpoint analysis.

The single-group design also shapes what the study can answer. A count of participants with patency could describe the experience of the evaluated group, but it would not provide a randomized estimate of how outcomes compare with another treatment. Design determines the scope of inference: statistical methods cannot create a control group or remove all alternative explanations when the design has none.

The record is also a reminder that statistical interpretation depends on documentation beyond a headline outcome. The definition of patency, assessment procedures, analysis population, and handling of missing measurements all affect how a count should be understood. Their absence from the registry record leaves important questions about measurement and analysis unresolved.

Finally, planning calculations and observed results serve different purposes. A planning illustration describes assumptions for a possible study size; it does not tell readers what happened to participants in this study or how precisely the primary outcome was estimated. Keeping these distinctions clear is essential when interpreting registry records, especially when outcome results and analysis details are not reported.

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 most consequential limitation of the registry information is that the primary endpoint result is not reported. The number with patency at 90 days and the number assessed are both unavailable, preventing calculation or interpretation of the endpoint's observed frequency. The registry lists enrollment but does not establish how many participants contributed to this outcome.

The single-group design has no concurrent comparator and is not a randomized comparison. It can describe outcomes in the group receiving the stent, but it cannot isolate a comparative effect. The registry also does not report the precise criteria used to define patency, how laboratory and clinical information were combined, or how assessments were scheduled within the stated timeframe.

Other important details are not reported in the registry record: the analysis population, missing-data methods, statistical analysis plan, sample-size justification, interim analyses, and multiplicity procedures. The record does not provide enough detail to assess whether outcome ascertainment was complete or how missing assessments might influence the result. Safety reporting includes zero recorded events in the listed categories, but event definitions and ascertainment methods are not described. These limitations restrict both efficacy interpretation and a fuller assessment of safety.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Prospective Evaluation of Winged Biliary Stent Patency in Patients With Benign Biliary Obstruction — NCT03115411.
• Registry record last updated 2019-04-16; status last verified 2019-04.
• Results first posted 2019-04-04.
• 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

The registry describes a completed, prospective, single-group evaluation of a winged biliary stent for benign biliary obstruction. Enrollment is listed as 23, and the primary endpoint is the count of participants with stent patency 90 days after placement, assessed using laboratory studies and clinical status. No separate comparator is reported.

The registry record does not report the primary endpoint count or its denominator, and it contains no analysis entries. Safety entries list 0 serious adverse events, 0 other adverse events, and 0 deaths in the Winged Stent group, with 23 at risk in each adverse-event category. These entries do not supply the missing patency result or permit a controlled comparison.