Bringing Simple Urge Incontinence Diagnosis & Treatment to Providers (BRIDGES): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Bringing Simple Urge Incontinence Diagnosis & Treatment to Providers (BRIDGES) (NCT00862745), a randomized phase 4 study. The primary outcome is Change in Frequency of Urge Urinary Incontinence Episodes at Week 12..

2. Clinical Question

The registry describes a Phase 4, randomized, triple-masked, parallel-group clinical trial. Its stated hypothesis was that fesoterodine would be more effective than placebo in reducing the mean number of urge incontinence episodes per day among women identified by the 3IQ. The posted primary outcome is the change in frequency of these episodes at Week 12, with baseline and Week 12 named as the measurement time points.

The registry record also describes an open-label clinical cohort study after the randomized phase. Participants who completed the 12-week trial would be offered open-label fesoterodine for an additional 9 months. That later cohort is distinct from the placebo-controlled comparison addressed by the primary Week 12 result. The record does not post a secondary outcome result for the longer-term phase.

The primary result therefore addresses a specific comparison, population, and follow-up point: the mean change in episode frequency over the randomized 12-week treatment period in the analyzed population. It does not, by itself, describe longer-term outcomes or other measures of urinary symptoms.

3. Trial Design

BRIDGES (NCT00862745) is registered as a completed Phase 4 trial sponsored by the University of California, San Francisco. The registry lists randomized allocation, triple masking, and a parallel-group model. The record gives an enrollment figure of 645. Its brief summary describes 636 women as intended for randomization; the record does not explain the difference between those figures.

The randomized comparison assigned participants to fesoterodine or matching placebo for 12 weeks. The active group began with fesoterodine 4 mg for 2 weeks, then could increase to 8 mg or remain at 4 mg for 10 weeks. The control group received an identical pill containing no medication, with a corresponding option to increase the placebo pill after the first 2 weeks. The posted primary outcome analysis includes participants who received at least one dose.

The registry describes the study as taking place at up to 14 clinical sites in the US. The recorded start is 2009-01 and the primary completion is 2010-05. The status is completed. Participants who completed the randomized trial were to be offered a further 9 months of open-label fesoterodine, according to the brief summary. The record does not report results from that longer-term cohort as a secondary outcome.

The primary endpoint was assessed at Week 12, with baseline and Week 12 specified as the measurement time points. The registry reports one primary outcome measure and one analysis. It identifies ANCOVA as the sponsor-reported analysis method, but does not report the model specification, covariates, or details of how missing endpoint measurements were handled. The original design assumptions, including any original sample-size justification, are not reported in the registry record.

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.

Before assignment: Participants screened over 4 week period.

Randomized Control Trial

Open-label Follow-up

Analysis population for the primary outcome, as defined in the registry: The population analyzed included all participants receiving at least 1 dose of study intervention.

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 Change in Frequency of Urge Urinary Incontinence Episodes at Week 12., measured over Baseline and Week 12.

The primary endpoint is change in the frequency of urge urinary incontinence episodes at Week 12. The measure is expressed as a mean number of episodes, with baseline and Week 12 identified as the time points. The registry describes the outcome as continuous and reports the group results as means with standard deviations.

Change from baseline is useful because it expresses how the measured episode frequency shifted during the randomized treatment period, rather than presenting only a Week 12 value. In this outcome, a negative change represents a decrease in episode frequency from baseline. Comparing the mean changes between randomized groups describes the difference in average change associated with assignment to the two study regimens in the analyzed population.

The registry reports a mean change of -2.5 episodes for fesoterodine and -1.8 episodes for placebo. The mean difference is reported as -0.7 episodes, with the comparison defined as fesoterodine relative to placebo. These summaries describe the average change; they do not show the range of individual participant responses. The standard deviations, 2.5 and 2.7 episodes, describe variability within each group.

This endpoint focuses on episode frequency. It does not directly represent other possible aspects of urinary symptoms, participant experience, or longer-term outcomes. The registry record does not report additional secondary outcome results.

7. Results Posted in the Registry

• Fesoterodine: mean -2.50 versus -1.80 on control; difference -0.70 (95% CI -1.12 to -0.28), standardized effect d = -0.27; z-test p = <0.001.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is a continuous measure: change in the mean frequency of urge urinary incontinence episodes from baseline to Week 12. The registry reports a mean and standard deviation for each randomized group. This method of summarizing a continuous measure makes the average change visible while the standard deviation conveys how spread out the observed changes are within each group.

What does the mean difference represent?

The posted comparison is the fesoterodine group mean change minus the placebo group mean change. The reported difference is -0.7 episodes. Since more negative change represents a greater reduction in episode frequency, the negative sign indicates that the average reduction was larger in the fesoterodine group in this comparison. The difference is a contrast between group averages; it is not a statement that every participant had that change.

The two group means are -2.5 episodes for fesoterodine and -1.8 episodes for placebo. Their standard deviations are 2.5 and 2.7. A standard deviation describes variability among the observations around a group mean. It is not the same as a confidence interval, and it does not indicate how precisely the group mean difference has been estimated.

What does ANCOVA do?

The registry identifies ANCOVA as the sponsor-reported method. In general, analysis of covariance compares outcomes between groups while accounting for one or more covariates in a statistical model. The registry record does not identify the covariates, the exact model specification, or whether the posted adjusted estimate and confidence interval are available. Its analysis entry reports p < 0.001, but does not give a numerical ANCOVA estimate or confidence limits.

A separate unadjusted recalculation from the posted summary statistics estimates the difference in group means without fitting the sponsor's ANCOVA model. It yields the posted comparison of -0.7 episodes and a confidence interval whose limits are both below zero. The recalculated contrast is therefore not a replacement for the sponsor's analysis: the methods are not identical, and the registry gives limited detail about the ANCOVA. The reported analysis remains the sponsor's stated method.

How should the p-value be read?

In general, a p-value measures how incompatible the observed data are with a specified statistical null model, under the assumptions of the analysis. A small p-value is evidence against that null model; it is not a measure of the probability that the null hypothesis is true, nor does it measure the size or importance of an effect. The registry's ANCOVA result is p < 0.001. The unadjusted recalculation is also reported as p < 0.001. Neither value alone describes the spread of participant outcomes or resolves questions about missing data and model assumptions.

For continuous outcomes, statistical inference depends on how the data are distributed and how the analysis handles variability. In general, the mean and standard deviation can be informative summaries, but they do not reveal the full outcome distribution. The registry record does not provide participant-level data, distributional diagnostics, or additional details of the analysis model. No further assumptions about these features can be checked from the posted summaries alone.

Why does variability matter?

In general, greater variability makes it harder to estimate a group difference precisely when other aspects of a study are unchanged. The standard deviations reported for this outcome are 2.5 and 2.7 episodes. They describe the observed spread within each group, whereas the confidence interval describes uncertainty around the estimated difference in group means. These are related but distinct concepts: participant-level variation can be substantial even when a group-level comparison is estimated with useful precision.

Over-dispersion is a general concern when count outcomes vary more than a statistical model's assumed distribution allows. If a model assumes less variability than the data contain, its uncertainty estimates may be too small. The registry identifies the primary analysis as ANCOVA and presents the outcome as a continuous mean change. It does not report a count-model analysis or diagnostics about over-dispersion. Thus, over-dispersion is a general statistical consideration for episode counts, not a reported finding about this trial's analysis.

What can the posted analysis establish?

The reported result addresses a difference in mean change at Week 12 among participants receiving at least one dose. The record reports one primary outcome and one analysis, with no secondary outcome results posted. It does not state the missing-data method, the analysis population beyond the at-least-one-dose description, or details of any multiplicity procedure. Those omissions limit assessment of the robustness of the inference, but they do not change what the reported group means and primary analysis say.

10. Confidence Intervals and Precision

The reported mean difference is -0.7 episodes, with fesoterodine compared with placebo. The unadjusted recalculation gives a 95% confidence interval that lies entirely below zero. The sponsor-reported ANCOVA result also has p < 0.001, but the registry does not provide numerical ANCOVA confidence limits or an adjusted estimate. The registry record therefore supports discussion of the unadjusted interval and the reported ANCOVA p-value, but not a comparison of adjusted and unadjusted interval widths.

In general, a confidence interval gives a range of values compatible with the data and the method used to calculate it. A 95% confidence interval is not a guarantee that the true effect has a 95% probability of falling within this particular interval. Its width reflects statistical precision: a narrower interval indicates a more precise estimate under the assumptions of the method, while a wider interval indicates greater uncertainty.

Here, the interval's position below zero indicates that the unadjusted estimate is inconsistent with a zero difference at the conventional level associated with a 95% interval. The point estimate gives the center of the comparison, while the interval conveys uncertainty around that estimate. Neither feature alone establishes whether the magnitude is important in practice. The registry record does not give a threshold for a clinically important change, so the posted statistical estimate cannot be classified against such a threshold.

The standard deviations of 2.5 episodes for fesoterodine and 2.7 for placebo describe spread among individual changes, not uncertainty in the estimated difference. The outcome counts of 303 and 301 also matter to the precision of the group comparison, but they do not erase the limitations of a summary-level analysis. The handling of missing Week 12 data and the details of the ANCOVA model are not reported in the registry record.

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 based on the observed effect rather than the trial's original design calculations. The planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation; each planning scenario uses the stated fraction of the observed effect. The original sample-size assumptions for the trial are not reported in the registry record.

The 80% power column gives the illustrative number of participants per arm for a design with an 80% chance of detecting the specified effect if that effect were the true one, under the listed assumptions. The 90% power column uses a higher target chance of detection and therefore gives a larger planning requirement for the same effect scenario. These are design calculations, not measures of what the completed trial achieved.

The effect scenarios are planning for 100%, 75%, and 50% of the observed effect. As the target effect becomes smaller, a study generally needs more participants to distinguish that effect from random variation at the same significance level and power target. The posted figures reflect that pattern: planning for 75% or 50% of the observed effect requires more participants per arm than planning for the full observed effect.

These calculations are not observed power. Observed power is not a useful substitute for interpreting the estimate and its confidence interval after a study has been completed. The planning illustrations instead show how sample-size needs change under specified assumptions and hypothetical target effects. They do not establish whether the original trial was adequately planned, because the trial's own design assumptions 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, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -0.700; pooled standard deviation σ = 2.602.
2. n = 2 × (1.96 + 0.842)² × 2.602² / -0.700² = 216.8, rounded up to 217 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
delta <- -0.7                      # observed difference in means
sigma <- 2.60159036461338                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^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 (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(862745)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 217 (80% power), 291 (90% power)
 75% of observed effect: n per arm = 386 (80% power), 517 (90% power)
 50% of observed effect: n per arm = 868 (80% power), 1,162 (90% power)
power.t.test: 217.8 
Simulated power at n = 217 per arm: 0.798 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-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. Analyses Reported by the Sponsor

The registry identifies ANCOVA as the sponsor-reported method and reports p < 0.001 for the comparison. It does not provide the ANCOVA estimate, its confidence interval, or details of the model specification. The analysis population is described as participants who received at least one dose of study intervention.

An unadjusted recalculation from the posted group summaries gives a mean difference of -0.7 episodes and a 95% confidence interval with both limits below zero. Its p-value is also reported as p < 0.001. The direction and reported level of statistical evidence are consistent with the sponsor's analysis. The recalculation is not the same as ANCOVA: it uses the posted summary statistics rather than the sponsor's model, and it cannot reproduce adjustments whose details are not reported.

The registry record indicates no discrepancy between the reported comparison and the recalculation. The sponsor's ANCOVA remains the reported analysis, while the recalculation is a simple unadjusted check based on summary values. Neither analysis resolves unreported questions about missing data or the ANCOVA model specification.

14. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome measure and one analysis, and no secondary outcome results are posted. This makes the primary Week 12 comparison the central statistical result available in the record. The registry does not report a multiplicity adjustment or a broader testing plan. It is therefore not possible to determine from the record whether additional analyses or outcomes were included in a prespecified testing strategy outside the posted results.

Multiplicity is a general issue that arises when multiple hypotheses are tested: without an appropriate plan, the chance of at least one false-positive result can increase across a set of tests. The registry record does not establish that such a problem occurred in this trial. It also does not provide enough information to assess any adjustment that might have been used beyond the single reported analysis.

The primary outcome population is described as participants who received at least one dose of study intervention. The registry does not explicitly identify this as an intention-to-treat analysis. It does not report the number randomized in each arm, the number with observed Week 12 measurements, or a detailed account of withdrawals for the primary endpoint. The handling of missing outcome data, including any imputation or sensitivity analyses, is not reported in the registry record.

Missing data can affect interpretation if participants with unobserved outcomes differ from those with observed outcomes. In general, the amount and pattern of missingness, together with the assumptions used to address it, help readers assess possible bias. Those details are not available in this record, so the effect of missing outcome data cannot be evaluated from the posted summaries.

The registry's safety counts use at-risk groups of 322 for fesoterodine and 323 for placebo, while the primary outcome counts are 303 and 301. The record does not explain this difference. These are distinct reported denominators for different analyses and should not be treated as interchangeable. The record also does not report a detailed analysis-population flow or a reconciliation of the counts.

15. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 2% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: hosptialized for myocardial infarction (0.3%), hospitalization for pulmonary embolus (0.3%), breast cancer (0.3%), hospitalization for colitis (0.3%), hospitalized for diabetes (0.3%).

The registry reports serious adverse events for 4 participants at risk in the fesoterodine group and 4 in the placebo group. The corresponding at-risk counts are 322 and 323. These are the serious-event figures recorded for the safety groups; they are separate from the primary outcome analysis counts.

The record also lists other adverse events affecting 148 participants at risk in the fesoterodine group and 88 in the placebo group. These figures describe the counts recorded under the other-adverse-event category. The registry does not provide enough detail to interpret the events' severity, duration, or relationship to study intervention.

Several serious-event terms are listed with 0.3% each: hospitalization for myocardial infarction, hospitalization for pulmonary embolus, breast cancer, hospitalization for colitis, hospitalization for diabetes, and hospitalization for shortness of breath. The percentages are reported for the listed terms; they should not be added together. The record does not provide further detail about event timing or causal attribution. Death counts are not reported in the registry record.

These summaries describe recorded events in the trial's safety groups. They do not, on their own, establish whether an event was caused by study intervention or characterize comparative safety across all possible outcomes. The posted safety figures should be read as counts and listed terms, not as a complete account of participants' clinical experiences.

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

The registry's primary result is a comparison of mean change in urge urinary incontinence episode frequency at Week 12. The fesoterodine group had a mean change of -2.5 episodes and the placebo group had a mean change of -1.8 episodes. The reported difference was -0.7 episodes, with the direction indicating a larger average reduction in the fesoterodine group. The sponsor-reported ANCOVA analysis had p < 0.001.

This is evidence of a difference in mean change under the reported analysis, not a description of every participant's experience. Group means conceal variation: the standard deviations were 2.5 and 2.7 episodes. Some participants may have had changes unlike their group average, but the registry's summaries do not describe individual outcome distributions or the proportion reaching a particular threshold.

The result is specific to the population identified by the 3IQ, the analyzed participants who received at least one dose, and the Week 12 endpoint. It does not establish outcomes for other populations, other symptom measures, or follow-up beyond the randomized period. Although the registry describes an open-label phase with an additional 9 months of fesoterodine offered to trial completers, no secondary result for that phase is posted.

Statistical evidence and clinical importance are different questions. The registry does not report a threshold for a clinically important change, so the mean difference cannot be classified against such a threshold from this record. Nor does a small p-value tell readers the probability that a treatment effect is true. The confidence interval and point estimate describe statistical uncertainty and magnitude; additional clinical context would be needed to interpret importance.

Finally, details that could affect interpretation are absent. The registry does not report how missing Week 12 measurements were handled, the ANCOVA model specification, or the original sample-size assumptions. The result should therefore be understood as the posted primary comparison, with those limitations in view, rather than as a complete account of all possible outcomes or analyses.

17. Why This Trial Matters Statistically

This trial is statistically notable for pairing a clinically recognizable screening approach, the 3IQ, with a randomized placebo-controlled comparison of a continuous symptom-frequency outcome. The primary question is expressed as a difference in mean change over a defined 12-week period. That framing lets readers distinguish the outcome being tested from broader claims about urinary symptoms or longer-term care.

The record also illustrates why statistical significance and effect size should be read together. The sponsor-reported ANCOVA result is p < 0.001, while the reported mean difference is -0.7 episodes and the group standard deviations are 2.5 and 2.7. The p-value conveys evidence against a null model under the analysis; the estimate and interval convey the size and precision of the group contrast. Neither alone settles whether the observed difference is important to participants.

Another useful statistical distinction is between the sponsor's adjusted method and an unadjusted recalculation from summary values. They give consistent directions and both report p < 0.001, but the recalculation cannot reproduce an ANCOVA model whose specification is not included in the registry record. This distinction helps readers understand what can be independently checked from summary data and what depends on details of the reported model.

Finally, the record includes both a planned open-label period and a completed randomized comparison, but no secondary results for the longer-term phase. Separating those phases prevents the Week 12 result from being extended beyond its measured outcome and time point. The registry's missing-data and original design details also show why a statistically significant result should be read alongside the methods information available, rather than as a complete statistical account.

18. 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 registry record does not explain the difference between its enrollment figure of 645 and the 636 women described in the brief summary as intended for randomization. The posted outcome counts are 303 for fesoterodine and 301 for placebo; the record does not provide a participant-flow account that reconciles these figures with enrollment or with the safety denominators.

The primary analysis population is described as participants who received at least one dose. The record does not state how missing Week 12 outcomes were handled, provide the number with observed endpoint data, or report sensitivity analyses. It also does not provide the ANCOVA covariates or model specification. These omissions limit assessment of the analysis and its robustness.

The registry reports a 12-week primary endpoint and describes a further open-label period of 9 months for participants completing the randomized trial. No secondary results for the longer-term period are posted. The primary result therefore cannot answer longer-term questions. The record also does not report a clinical-importance threshold for interpreting the mean difference.

The adverse-event summaries give counts and selected serious-event terms, but the registry does not report event timing, causal attribution, or a detailed account of safety-data collection in the material summarized. Death counts are not reported in the registry record. These omissions mean the listed safety figures should not be treated as a full characterization of safety.

The original sample-size justification, original design assumptions, and details of any interim analyses or broader statistical plan are not reported in the registry record. The posted planning illustrations are based on the observed effect and do not reconstruct the original design rationale. Finally, the record describes up to 14 US clinical sites, but does not give site-specific results or details that would allow assessment of how outcomes varied across sites.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Bringing Simple Urge Incontinence Diagnosis & Treatment to Providers (BRIDGES) — NCT00862745.
• Registry record last updated 2011-11-24; status last verified 2011-10.
• Results first posted 2011-11-24.
• 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.

22. Record Summary

BRIDGES (NCT00862745) is a completed Phase 4, randomized, triple-masked, parallel-group trial sponsored by the University of California, San Francisco. It compared 12 weeks of fesoterodine with matching placebo in women diagnosed with urge urinary incontinence using the 3IQ. The registry lists enrollment of 645 and gives 2009-01 as the start and 2010-05 as primary completion.

The primary endpoint was change in mean urge urinary incontinence episodes at Week 12. The reported mean changes were -2.5 episodes for fesoterodine and -1.8 for placebo, with a mean difference of -0.7 episodes. The sponsor-reported ANCOVA result was p < 0.001. The analysis population included participants receiving at least one dose.

The record describes an open-label period of an additional 9 months for randomized-trial completers, but posts no secondary outcome results. Details of missing-data handling, the ANCOVA specification, and original sample-size assumptions are not reported in the registry record.