Cranberry Effect on Urinary Tract Infections: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Cranberry Effect on Urinary Tract Infections (NCT02996981), a registered phase not stated study. The primary outcome is The Incidence of UTI.

2. Clinical Question

3. Trial Design

This record describes a retrospective chart review using the EPIC database. Its stated purpose was to examine whether adding cranberry juice capsules to the discharge medication regimen reduced UTI incidence among patients discharged home with an indwelling urinary catheter after pelvic floor gynecologic surgery. The study status is completed. The registry lists enrollment of 167, a start date of 2016-11-21, and a primary completion date of 2017-07-14.

The groups were drawn from different time periods. The cranberry group included patients undergoing surgery between April 2016 and September 2016. The no cranberry group included patients undergoing surgery between April 2015 and September 2015 and not prescribed cranberry juice capsules. The registry lists 96 participants at risk in the cranberry group and 71 in the no cranberry group for the reported adverse-event figures.

This is not a randomized comparison. The registry says allocation was not stated and cautions that the arms are not a like-for-like control comparison. Because the groups belong to different calendar periods, treatment status is also linked to when surgery occurred. General statistical interpretation: differences between groups can reflect the intervention, but they can also reflect differences in patient characteristics, clinical practice, recordkeeping, or other factors that change over time. The registry does not report enough detail to determine whether such factors were measured or adjusted for.

The record identifies one primary outcome measure and one analysis, but the statistical method used for that analysis is not reported in the registry record. The protocol, eligibility details beyond the description of the groups, and any planned adjustment strategy are also not reported. The primary endpoint is UTI within 6 weeks postoperative; the group-specific endpoint results are not reported.

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 The Incidence of UTI, measured over within 6 weeks postoperative.

The primary endpoint is titled The Incidence of UTI and is measured as the count of participants with a UTI within 6 weeks postoperative. It is a binary participant-level outcome: each person either has the event during the stated period or does not. A count of participants with an event can describe how many people in each group experienced the endpoint, provided the number assessed in each group is also known.

General explanation: a fixed follow-up window gives the endpoint a defined period in which events are counted. This makes the outcome interpretable as the occurrence of UTI during that window, rather than as an event rate over an unspecified duration. It does not, by itself, show when within the window an event occurred or account for different lengths of follow-up if those differ between participants.

UTI incidence is the direct outcome named in the study objective, so it aligns with the question the review set out to examine. However, the registry does not report the number of participants with UTI in either group, the number evaluated for this endpoint, or an estimated comparison between groups. Consequently, the endpoint definition is available, but the primary result cannot be interpreted quantitatively from the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The record describes a retrospective chart review. General explanation: retrospective studies use information already recorded in clinical records rather than assigning participants prospectively to study groups. Such records can support a comparison, but the strength of the comparison depends on how groups were formed, how consistently outcomes were documented, and whether relevant differences between groups were addressed. The registry does not report details of data abstraction, outcome validation, or a statistical adjustment plan.

What does a binary endpoint mean?

The primary outcome is a count of participants with UTI within 6 weeks postoperative. A binary endpoint classifies each participant according to whether the event occurred within the defined period. Group counts are useful, but interpreting them requires knowing how many participants in each group were assessed for the endpoint. A comparison can then be expressed using measures such as an absolute difference in event proportions or a relative measure. General explanation: these measures answer different questions, and the choice should be specified by the analysis plan. The registry does not report the primary event counts, evaluable denominators, effect measure, or analysis method.

What does uncertainty add?

General explanation: an estimate from a study is affected by sampling variation. A confidence interval represents uncertainty around an estimated effect under the assumptions of the method used. A narrow interval indicates greater precision than a wide interval, although interpretation also depends on the endpoint and design. A p-value is a measure tied to a particular statistical test and null hypothesis; it is not a measure of the probability that a treatment works. No confidence interval or p-value for the primary UTI comparison is reported in the registry record.

Why does the group formation matter?

The cranberry and no cranberry groups come from separate calendar periods. The record says the comparison was not randomized, allocation was not stated, and the arms are not a like-for-like control comparison. General explanation: random allocation, when used, is intended to make treatment groups comparable on average with respect to both measured and unmeasured baseline factors. In an observational historical comparison, that protection is not posted by the design. Group differences may be associated with the outcome, and changes in clinical practice or documentation over time may also affect the recorded comparison. Statistical adjustment can address some measured differences, but cannot guarantee removal of bias from unmeasured factors. Whether adjustment was undertaken is not reported.

What can over-dispersion mean?

General explanation: over-dispersion occurs when outcome variability is greater than a statistical model assumes. It is a concern in some count-data analyses because a model that understates variability can make uncertainty appear too small. The primary endpoint in this record is a participant count for a binary outcome, not a reported recurrent-event count. The registry does not report a model, a dispersion estimate, or a method that would allow over-dispersion to be assessed for the primary analysis.

How should sample-size illustrations be read?

The registry's planning description says sample-size illustrations are based on a fraction of the observed effect, use a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation. It also distinguishes the interpretation for time-to-event outcomes from other outcomes. General explanation: such calculations describe the number of participants that a hypothetical design might require under stated assumptions; they do not measure the probability that the completed study detected an effect. They are planning illustrations, not observed power. The underlying numerical illustrations and primary observed effect are not reported in the registry record, so the assumptions cannot be independently evaluated from this record.

In this comparison, equal-allocation planning assumptions do not describe the reported group sizes, which are 96 and 71 in the adverse-event entries. More importantly, a planning calculation cannot compensate for missing primary endpoint results or the limitations of a historical comparison. The specific statistical test, model, covariate set, treatment of missing data, and method for calculating uncertainty are not reported. General statistical concepts can clarify what such methods would do, but the record does not support attributing any particular method or result to this study.

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("Cranberry Group", "No Cranberry Group")
n      <- c(96, 71)
events <- c(66, 54)
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  Cranberry Group  96  66  68.8  58.5  77.8  58.9  77.1  58.9  77.1
ARM  No Cranberry Group  71  54  76.1  64.5  85.4  65.0  84.5  64.9  84.5

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome measure and one analysis. This indicates a single registered primary outcome and analysis entry, but it does not disclose whether the analysis included multiple statistical tests, multiple model specifications, or additional outcomes outside that entry. Any multiplicity strategy, such as adjustment of significance thresholds across tests, is not reported in the registry record. Without a complete analysis plan, the implications of multiple testing cannot be assessed.

Missing-data handling is also not reported. The record does not state how many participants had primary endpoint information available, whether all enrolled participants were included in the primary analysis, how incomplete follow-up was handled, or whether any assumptions were used to address missing outcomes. The adverse-event denominators should not be assumed to be the primary endpoint denominators because the registry does not explicitly identify them as such.

Analysis populations are not reported in the registry record. In general, an analysis population defines which participants contribute to an estimate and how deviations, incomplete records, or changes in exposure are treated. These choices can affect the interpretation of a nonrandomized comparison as well as the amount of information available. The group descriptions and enrollment count alone do not specify the population used for the primary analysis.

Because primary UTI counts, evaluable denominators, and missing-data methods are absent, neither the endpoint comparison nor the potential impact of missing records can be reconstructed from the registry entry. This uncertainty is separate from multiplicity: reporting one registered outcome does not resolve missing endpoint data or establish that only one statistical test was conducted.

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.

The registry lists zero serious adverse events and zero other adverse events in the cranberry group, with 96 participants at risk. It also lists zero serious adverse events, zero other adverse events, and zero deaths in the no cranberry group, with 71 participants at risk. These are the safety figures reported in the registry record.

General explanation: zero recorded events means that no events in the listed categories were entered for those groups in this record. It does not prove that an event is impossible or that the intervention has no safety risks. Interpretation depends on how events were defined, collected, monitored, and reported, and those details are not reported in the registry record. The entry also does not give a separate description of safety follow-up or adjudication.

The safety counts should be kept distinct from the primary endpoint. The primary outcome is UTI within 6 weeks postoperative, whereas the adverse-event entries report serious events, other events, and deaths. The zero adverse-event counts do not supply the missing UTI counts and should not be interpreted as showing that no UTIs occurred.

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

The registry establishes what the study set out to examine: whether UTI incidence within 6 weeks postoperative differed between patients prescribed cranberry juice capsules and patients not prescribed them after pelvic floor gynecologic surgery with discharge home using an indwelling urinary catheter. It also establishes that the comparison was retrospective and involved groups from different calendar periods.

The registry does not report the primary outcome counts or a statistical estimate comparing the groups. It therefore does not show the observed direction, size, or precision of the UTI comparison. The absence of primary results is not a finding of no difference, and it is not evidence that the groups had the same incidence. Nor does the record support a conclusion that cranberry capsules reduced or increased UTI incidence.

Even if a group contrast were available, the design would require cautious interpretation. The registry says the comparison was not randomized and that the arms are not a like-for-like control comparison. General explanation: when groups differ in characteristics or are treated in different periods, the observed outcome contrast may reflect those differences as well as the exposure being studied. Statistical adjustment can help with measured factors, but the registry does not report whether adjustment was performed or what factors were considered.

The study is consequently informative as a record of a clinical question and a retrospective comparison, but the posted results are insufficient to evaluate the primary endpoint. The stated enrollment and safety entries do not replace the missing outcome data. No inference about the magnitude of a possible effect, the statistical compatibility of the results with a null hypothesis, or the clinical importance of a difference can be made from the registry record alone.

14. Why This Trial Matters Statistically

This study illustrates why a clearly stated endpoint is only one part of a statistically interpretable trial record. The primary question and follow-up window are identifiable: UTI within 6 weeks postoperative among patients discharged with an indwelling urinary catheter after pelvic floor gynecologic surgery. But without endpoint counts, denominators, and an estimate of the comparison, readers cannot assess the observed outcome or its uncertainty.

It also demonstrates the importance of distinguishing randomized trials from historical comparisons. The two groups came from different calendar periods, and the registry explicitly cautions that they are not a like-for-like control comparison. General statistical lesson: the design determines which explanations of an observed difference remain plausible. In a nonrandomized comparison, measured and unmeasured group differences can complicate causal interpretation, while changes over time can introduce additional sources of variation.

Finally, safety reporting and efficacy-related outcome reporting answer different questions. The record lists zero serious and other adverse events in both groups, but those entries do not report the primary UTI endpoint. Complete interpretation requires knowing what each result represents, its denominator, and how it was analyzed. In this record, important statistical details—including the primary results, analysis method, and handling of missing data—are not reported. That makes careful distinction between a study objective and a reported finding essential.

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 statistical interpretation is that the registry does not report group-specific UTI counts, the number assessed for the primary endpoint, or an estimated comparison. No confidence interval or p-value for the primary outcome is reported. The incidence comparison therefore cannot be quantified from this record.

The study is a retrospective chart review, and the groups were drawn from different calendar periods: April 2015 to September 2015 for the no cranberry group and April 2016 to September 2016 for the cranberry group. The registry states that this was not a randomized comparison, that allocation was not stated, and that the groups are not a like-for-like control comparison. Differences between groups or changes over time could affect a comparison; whether these possibilities were assessed or adjusted for is not reported.

The registry does not report detailed eligibility criteria, the cranberry capsule regimen, how UTI was defined or ascertained, or how consistently follow-up information was available. It also does not report missing-data procedures, the analysis population, the statistical method, or the covariates used in any adjustment. These omissions prevent assessment of the primary analysis assumptions and of possible bias from incomplete records or group differences.

The adverse-event entries list zeros, but the registry does not report further details about event collection or monitoring. Those figures do not resolve the missing primary endpoint results. The record also does not report a sample-size justification for the original study or enough numerical detail to assess planning illustrations. These limitations restrict what can be inferred from the posted record; they do not establish that the underlying chart review lacked additional information.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Cranberry Effect on Urinary Tract Infections — NCT02996981.
• Registry record last updated 2023-08-31; status last verified 2022-10.
• Results first posted 2023-08-31.
• 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

NCT02996981 is a completed retrospective chart review sponsored by TriHealth Inc. It examined UTI incidence within 6 weeks postoperative among patients discharged home with an indwelling urinary catheter after pelvic floor gynecologic surgery. The cranberry group came from April 2016 to September 2016; the no cranberry group came from April 2015 to September 2015.

The registry lists enrollment of 167 and describes the comparison as nonrandomized, with allocation not stated and arms that are not a like-for-like control comparison. It reports one primary outcome measure and one analysis, but does not report the primary UTI counts or comparison estimate. The adverse-event entries list zero serious and other adverse events in each group and zero deaths in the no cranberry group. The statistical method and handling of missing data are not reported in the registry record.