This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Evaluation of Ureteral Stents in the Management of Stone Disease (NCT02211313), a randomized na study. The primary outcome is Change From Baseline in Pain on the 10-point Analog Pain Scale at Day 7 Post Stent Removal..
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT02211313 |
| Phase | NA |
| Condition | Urinary Stones, Urinary Tract Stones |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Single |
| Enrollment | 41 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Washington University School of Medicine |
| Results posted | Yes |
2. Clinical Question
Population
People undergoing treatment for urinary stone disease. The registry record lists urinary stones and urinary tract stones as conditions. It does not report further eligibility details or a description of the primary-outcome analysis population.
Intervention
A soft, 6 French ureteral stent. The trial description says participants were randomized to a size 6 French soft stent or a size 6 French hydrophobic stent.
Comparator
A hydrophobic, 6 French ureteral stent. The registry record describes both arms as using size 6 French stents, so the intended comparison concerns stent composition rather than a difference in the listed size.
Primary question
What is the change from baseline in pain on the 10-point Analog Pain Scale at day 7 after stent removal, compared between the soft and hydrophobic stent arms? The outcome is described as a mean with standard deviation, but a single arm-level comparison and its uncertainty are not reported in the registry record.
The clinical question focuses on patient-reported pain after the temporary stent has been removed. The registry’s background describes stents as a way to support drainage in the setting of an obstructing stone or postoperative ureteral swelling, while noting that stents can cause discomfort and bother. It also states that smaller and softer stents have become available and that research on their relative benefits has been conflicting. These statements explain the motivation for comparing stent characteristics; they are not findings from this trial.
The planned contrast is between two 6 French devices that differ in the listed material or composition description. The registry does not specify a broader comparison with no stent, nor does it identify a separate comparison of stent sizes. It describes the outcome as change from baseline in pain at a follow-up time point after removal. The record does not provide the arm-specific baseline and follow-up means, the calculated change scores, or a treatment-effect estimate with a confidence interval. Consequently, the clinical question can be described, but the size and precision of the observed contrast cannot be evaluated from the posted outcome record.
3. Trial Design
The registry describes a randomized, single-masked, parallel trial of ureteral stents for urinary stone disease. Participants were assigned to a soft 6 French stent or a hydrophobic 6 French stent. The recorded enrollment is 41. That enrollment figure is not an arm-level outcome denominator, and the registry does not state how many participants contributed primary-outcome data in either arm.
Randomization is intended, in general, to make treatment groups comparable with respect to both measured and unmeasured characteristics at the point of assignment. It does not guarantee that groups will be identical, especially when the enrolled sample is limited, and it does not by itself prevent differences in follow-up, outcome availability, or analysis populations. The record identifies random allocation but does not report the sequence-generation method, allocation concealment procedures, or details of how assignments were implemented.
The design is described as single-masked. The registry record does not report which people were masked, how masking was maintained, or whether it could have been affected by recognizable differences between the devices. Masking can matter when a study measures a subjective outcome such as pain, because expectations may influence reporting or assessment. That is general statistical context, not a claim about what happened in this trial.
The parallel model means the record describes participants as assigned to an arm rather than as switching between the two stents. The trial status is terminated. The record lists a start date of 2014-08 and primary completion on 2018-04-03, but does not state why the trial was terminated or describe the circumstances of its completion. A reason for termination, the planned recruitment target, and a sample-size justification are not reported in the registry record. The enrollment figure alone does not establish whether recruitment matched the original plan or whether the trial had adequate precision for its primary question.
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
| Stage | Ureteral Stent - Soft, 6 French | Ureteral Stent - Hydrophobic, 6 French |
|---|---|---|
| STARTED | 18 | 23 |
| COMPLETED | 12 | 20 |
| NOT COMPLETED | 6 | 3 |
Reasons for not completing this period:
| Reason | Ureteral Stent - Soft, 6 French | Ureteral Stent - Hydrophobic, 6 French |
|---|---|---|
| Treatment Failure | 5 | 2 |
| No Follow up Questionnaires | 1 | 1 |
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.
| Characteristic | Unit | Ureteral Stent - Soft, 6 French | Ureteral Stent - Hydrophobic, 6 French | Total |
|---|---|---|---|---|
| Participants analysed | 18 | 23 | 41 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 6 | 15 | 21 |
| Age, Categorical: >=65 years | Participants | 6 | 5 | 11 |
| Sex: Female, Male: Female | Participants | 6 | 13 | 19 |
| Sex: Female, Male: Male | Participants | 6 | 7 | 13 |
| Race/Ethnicity, Customized: Race – African American | Participants | 0 | 3 | 3 |
| Race/Ethnicity, Customized: Race – Caucasian | Participants | 12 | 17 | 29 |
| Region of Enrollment: United States | Participants | 12 | 20 | 32 |
6. Primary Endpoint
The registry lists the primary outcome as Change From Baseline in Pain on the 10-point Analog Pain Scale at Day 7 Post Stent Removal., measured over Baseline, day 7 post stent removal.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Standard Deviation |
| Unit | Scores on a scale 0-10 (Numeric) |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is change from baseline in pain on the 10-point Analog Pain Scale at day 7 after stent removal. The scale is described as running from 0 for no pain to 10 for the worst possible pain, with each point representing one unit on the scale. The registry lists the outcome as a mean and standard deviation, which indicates a continuous measure summarized using an average and a measure of spread.
Pain is relevant to the stated purpose because the trial’s background describes discomfort and bother as concerns associated with ureteral stents. A patient-reported pain scale can capture the intensity of an experience that is not directly measured by a laboratory test or imaging measure. Recording pain after stent removal also sets the outcome at a defined point relative to the procedure. The record gives the timeframe as baseline and day 7 post stent removal.
In general, a change score represents the difference between a participant’s follow-up and baseline measurements. Comparing changes between randomized arms can describe whether the average pattern over that interval differed between the assigned devices. The registry does not explain the precise sign convention used for change, so the direction in which a positive or negative value would indicate more pain is not reported in the registry record.
The record does not include the observed arm means, standard deviations, number of analyzed participants, or a single between-arm estimate for this endpoint. It therefore does not establish the magnitude or precision of any difference in pain change. The endpoint’s definition identifies what the trial intended to assess; it is not itself evidence of an effect.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry establishes the comparison of interest: change in pain from baseline to day 7 after stent removal for participants assigned to soft or hydrophobic 6 French ureteral stents. However, it does not report a single comparison for this primary outcome. The record explicitly indicates that the primary outcome has several categories or time points and was not reduced to one comparison. Although the registry lists one outcome measure, it records no analyses. As a result, there is no posted treatment-effect estimate, confidence interval, or p-value to interpret for the primary question.
This absence of a single result is different from a finding of no difference. Without an estimate, readers cannot tell whether the observed arm averages were close together or far apart, whether the estimate was precise or uncertain, or which direction the contrast took. The registry record also does not report the arm-level means and standard deviations needed to understand the outcome distributions. No conclusion about the relative pain outcomes of the stent groups follows from the outcome entry alone.
The study’s recorded enrollment is 41, but that figure should not be treated as the number contributing data to the pain comparison. The primary-outcome denominator by arm, the handling of missing measurements, and the analysis population are not reported in the registry record. In general, the amount and pattern of missing outcome data can affect both the interpretation and precision of an estimated treatment contrast. The enrollment total cannot resolve those questions.
The sample-size assumptions describe a planning illustration based on a fraction of an observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. Such illustrations are not observed effects or observed power. Because a single primary-outcome effect is not reported in the registry record, the planning assumptions cannot be used to recover the trial result or to assess the precision of the actual comparison. A sample-size calculation also does not substitute for an observed estimate and its uncertainty.
The status is recorded as terminated, but the reason for termination is not reported in the registry record. The status alone does not show why the trial ended, whether termination affected the planned analyses, or how the result might have differed under another recruitment or follow-up pattern. The posted information therefore supports a description of the randomized comparison and endpoint, but not an efficacy conclusion or a quantitative assessment of the primary outcome.
9. Statistical Methods Explained
The registry describes a randomized comparison and a continuous primary outcome, but it does not post a single analysis of that outcome. The concepts below explain how such results are generally read; they do not describe unreported procedures as having been used in this trial.
What does a mean describe?
For a continuous outcome such as a pain score or change in pain score, the mean is the arithmetic average of the participant-level values included in an analysis. It gives a useful summary of the group’s central tendency, but it does not describe every participant’s experience. The standard deviation describes how dispersed individual values are around the mean. A larger standard deviation indicates more variation among the values, while a smaller one indicates that values are more clustered. Neither summary alone shows how much the two randomized groups differ.
For the trial’s stated endpoint, the group means would need to be interpreted alongside a clearly defined change-score direction and the number of participants contributing data. Baseline measurements can help readers understand the starting pain levels, while the follow-up values describe pain at the stated assessment time. A comparison of change scores is not interchangeable with a comparison of follow-up means unless the relevant analysis and assumptions support that interpretation. The registry does not report the values or the analysis details needed to make that assessment.
What would a treatment-effect estimate show?
A between-arm estimate would express the contrast in average pain change between participants assigned to the soft stent and those assigned to the hydrophobic stent. The sign depends on which arm is subtracted from which and on how change is defined. Because the registry does not state a sign convention or report an estimate, the direction and magnitude of the contrast cannot be inferred.
A confidence interval, when reported, gives a range of values compatible with the data under the analysis and its assumptions. A narrow interval indicates greater precision than a wide interval. The interval is not a guarantee that the true effect lies within its endpoints, and it does not by itself determine whether a difference is clinically important. Interpreting it requires the estimate, the interval, the outcome scale, and context about what differences matter. None of those result details is posted as a single primary-outcome comparison in the registry record.
A p-value is a measure of how incompatible the observed data are with a specified null model, under the assumptions of the statistical test. It is not the probability that the null hypothesis is true, and it does not measure the size or importance of an effect. The registry record does not report a primary-outcome p-value. Without an estimate and uncertainty interval, a p-value alone, even if it were available, would not communicate the magnitude or precision of the pain contrast.
Why does randomization matter?
Random assignment is generally used to reduce systematic differences between treatment groups at the time of assignment. When properly implemented and retained in analysis, it supports interpreting between-group contrasts as comparisons of assigned interventions. Randomization does not remove uncertainty from random variation, ensure balance in every characteristic, or prevent bias from missing outcomes and deviations after assignment. The registry identifies randomized allocation but does not report sequence generation, concealment, or the specific analysis population.
Masking can reduce the influence of expectations on treatment delivery, participant reporting, or outcome assessment. That is particularly relevant to a self-reported experience such as pain. The record says the study was single-masked but does not identify who was masked or describe the masking procedures. It is therefore not possible to assess from the registry how masking applied to the pain measurement.
How should the planning illustration be understood?
The stated planning assumptions use a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation. The illustration is described as using a stated fraction of the observed effect. A planning calculation estimates the sample size that would be needed under its chosen assumptions; it does not report what happened in the trial. It is also not observed power. Since the registry does not report a single observed primary-outcome effect, readers cannot assess the effect value underlying the illustration from the posted outcome record.
General sample-size planning depends on the target effect, variability, significance level, desired power, allocation, and analysis method. Changing these assumptions can change the planning result. A calculation based on a fraction of an observed effect is a scenario, not evidence that the trial achieved that effect or that a particular conclusion is reliable. The registry does not report a sample-size justification for the trial’s design, so the planning illustration should not be treated as that justification.
What does the absence of an analysis mean?
The registry lists no analyses and does not reduce the outcome’s several categories or time points to one comparison. This limits interpretation: there is no posted estimate to assess, and the record does not make clear which time point or category-level data would support a particular contrast. It would be inappropriate to reconstruct an analysis from incomplete summaries or to substitute a planning assumption for an observed result. General statistical principles can clarify how a reported comparison would be read, but they cannot supply the missing analysis.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists one primary outcome measure but states that the outcome has several categories or time points and was not reduced to one comparison. It does not report which categories or time points were analyzed, whether any were designated as primary among those choices, or how multiple comparisons were handled. These details are not reported in the registry record.
In general, multiplicity arises when several hypotheses, outcomes, time points, or subgroup contrasts are examined. The more comparisons made, the greater the chance that at least one result may appear noteworthy by chance if each is interpreted without accounting for the collection of tests. Statistical approaches can address this issue, but the approach depends on the analysis plan and the scientific questions. No multiplicity procedure is reported in the registry record, so it is not possible to assess how the several categories or time points relate to any inferential claims.
The record does not describe missing primary-outcome observations, reasons for missingness, or the method used to handle them. It also does not report whether all randomized participants were included in the primary analysis, whether analyses followed assigned groups, or whether a different analysis population was used. Those details are not reported in the registry record. In general, missing data can reduce precision and can bias comparisons if the probability of having an observed outcome is related to the outcome itself or differs between groups.
The registry’s enrollment figure should not be assumed to be the outcome-analysis denominator. Arm-specific numbers with available baseline and follow-up pain scores are not reported in the registry record. Without the denominators, analysis-population definition, and missing-data approach, readers cannot determine how complete the primary endpoint was or how robust an estimate might be to missing observations.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Ureteral Stent - Soft, 6 French | 0 | 12 | 0.0% |
| Ureteral Stent - Hydrophobic, 6 French | 0 | 20 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Ureteral Stent - Soft, 6 French | 0 of 12 |
| Ureteral Stent - Hydrophobic, 6 French | 0 of 20 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Ureteral Stent - Soft, 6 French | 0 of 12 |
| Ureteral Stent - Hydrophobic, 6 French | 0 of 20 |
The registry reports serious adverse event figures separately for the soft and hydrophobic stent groups. For the soft 6 French stent group, 12 participants were listed as at risk for serious adverse events and 0 were affected. For the hydrophobic 6 French stent group, 20 were listed as at risk and 0 were affected. The recorded deaths were 0 in each group. These are the posted serious-event counts, not evidence that no other kinds of adverse events occurred.
The “at risk” figures are the denominators shown for these safety entries. They should not be replaced by the overall enrollment figure, and they should not be assumed to be the primary-outcome analysis denominators. The registry also records zero affected for other adverse events in each group, with the same group-specific at-risk figures. The record does not provide additional detail on the event collection period, definitions, or how the safety populations were determined.
In general, a count of zero observed events means that no events of the recorded type appear in the reported group data; it does not establish that the underlying risk is zero. Safety interpretation depends on the amount and duration of observation, the event definitions, completeness of reporting, and the population at risk. The registry’s adverse-event entry does not support a broader conclusion about safety beyond the listed counts.
12. What the Result Does, and Does Not, Mean
The record describes a randomized comparison of soft and hydrophobic 6 French ureteral stents and names change in pain at day 7 after stent removal as the primary outcome. This identifies the clinical question and the intended measurement. It does not provide a single estimate of the difference between arms, its uncertainty, or a p-value. Therefore, the posted outcome information does not show the direction, size, or precision of the primary comparison.
The missing comparison should not be interpreted as evidence that the stents produced the same pain outcomes. Nor does the registry entry establish that one device produced more or less pain. Those conclusions require observed outcome data and a clearly described analysis. The scale definition and outcome title clarify what was intended to be measured, but they are not substitutes for the measured values.
The design information also has limits. Randomized allocation is recorded, and the study is described as single-masked and parallel. However, the registry does not identify who was masked, give the allocation procedures, or explain the analysis population. These omissions do not prove that the procedures were inadequate; they mean that the registry does not provide the details needed to evaluate them.
Similarly, the record’s terminated status does not reveal why the trial was terminated or what role the decision played in recruitment, follow-up, or analysis. The recorded enrollment of 41 cannot establish the number with evaluable pain measurements or the precision of a treatment estimate. The sample-size assumptions are planning illustrations, not trial results, and cannot fill the gap left by the missing comparison.
The serious adverse event entries report zero affected participants in each listed group, with the group-specific at-risk counts recorded in the safety data. Those observations describe the posted safety counts; they do not establish absence of risk or speak to outcomes not included in those entries. Overall, the record supports a description of the trial design, endpoint, and listed safety counts, but it does not support a quantitative conclusion about comparative pain outcomes.
13. Why This Trial Matters Statistically
This trial is statistically informative as an example of the distinction between a registered question and a reported result. The record gives a randomized comparison, identifies the devices, and defines a patient-reported primary endpoint. Those details allow readers to understand what the investigators intended to compare. Yet the registry does not present a single outcome comparison, so the central statistical question cannot be answered from the posted primary-outcome information.
That distinction matters because a trial’s design description and its outcome evidence serve different purposes. Randomization describes how treatment assignment was intended to occur. The endpoint describes what was measured. An estimate and its uncertainty would describe what the observed data indicate about the contrast. The first two cannot stand in for the third. Without the result, neither the direction nor precision of a difference can be evaluated.
The record also illustrates why denominators and analysis populations matter. An overall enrollment count is not necessarily the number of people with complete baseline and follow-up pain measurements, nor does it identify the participants included in a particular analysis. In general, transparent reporting of group-specific denominators, missing data, and analysis methods helps readers judge how closely a result reflects the randomized comparison.
Finally, reporting that an outcome spans several categories or time points without presenting a single comparison leaves uncertainty about which contrast should answer the primary question and how multiplicity was addressed. These are not merely technical details: they determine how precisely and fairly the observed data can be interpreted. The available record therefore has value for understanding the intended design, while also leaving substantial limits on statistical interpretation of the primary endpoint.
14. Limitations
- The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
- Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.
The principal limitation for interpreting the trial is that the registry does not report a single comparison for its primary pain outcome. It describes the outcome as having several categories or time points and records no analyses. Arm-level means, standard deviations, treatment-effect estimates, confidence intervals, and p-values for a single primary comparison are not reported in the registry record.
The denominator for the primary analysis is also unavailable. Although the recorded enrollment is 41, the numbers with baseline and day 7 pain measurements in each arm are not reported. The registry does not describe missing measurements, reasons for missingness, or how missing data were handled. Consequently, neither completeness of outcome follow-up nor the possible effect of missingness can be assessed from the record.
Details of randomization and masking are limited. The record identifies randomized allocation and single masking but does not describe sequence generation, allocation concealment, who was masked, or how masking was maintained. These omissions limit assessment of implementation; they do not establish that procedures were or were not followed.
The registry records the trial as terminated, but the reason and its implications for recruitment, follow-up, and analysis are not reported. It also does not state the original recruitment target or a trial-specific sample-size justification. The planning assumptions are illustrative and do not provide an observed effect estimate.
For safety, the registry reports the listed adverse-event counts but does not give further information about collection periods, event definitions, or the construction of the at-risk populations. The available safety counts therefore have a limited scope. These reporting gaps constrain what can be concluded from the registry record; they should not be filled with assumptions about the protocol or unreported results.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Evaluation of Ureteral Stents in the Management of Stone Disease — NCT02211313.
- Registry record last updated 2019-06-05; status last verified 2019-05.
- Results first posted 2019-05-21.
- 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.
Continue through the Clinical Biostats statistical pathway
Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
18. Record Summary
The registry record describes a randomized, single-masked, parallel trial of soft versus hydrophobic 6 French ureteral stents for urinary stone disease. It records enrollment of 41, a start date of 2014-08, primary completion on 2018-04-03, and status as terminated.
The primary outcome is change from baseline in pain on the 10-point Analog Pain Scale at day 7 after stent removal, summarized as a mean and standard deviation. The registry does not report a single comparison for this outcome and lists no analyses. The reason for termination, primary-outcome analysis denominators, missing-data methods, and analysis populations are not reported in the registry record.
For serious adverse events, the record lists 0 affected among 12 at risk in the soft-stent group and 0 affected among 20 at risk in the hydrophobic-stent group; deaths are recorded as 0 in both groups. These counts describe the posted safety entries and do not provide a comparative pain result.