Resveratrol for Pain Due to Endometriosis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Resveratrol for Pain Due to Endometriosis (NCT02475564), a randomized phase 4 study. The primary outcome is Pain Scores Measured by VAS (Visual Analog Scale) at Day 42..

2. Clinical Question

The clinical question is therefore about the added effect associated with resveratrol in the setting of this shared contraceptive-pill regimen. It is not a comparison of the pill against no pill, or of resveratrol alone against placebo alone. The brief summary describes the outcome as pelvic pain at the end of 2 months of treatment. The arm descriptions and the primary endpoint specify 42 days; the registry record does not explain the difference in those descriptions.

The record also lists serum CA125 and serum prolactin levels at 42 days as secondary outcomes. They are distinct from the primary pain question. Results sufficient to describe those secondary comparisons are not reported in the registry record.

3. Trial Design

The registry classifies this as a phase 4, randomized, triple-masked, parallel-group trial. Its status is completed. The listed sponsor is Hospital de Clinicas de Porto Alegre. The registry records the study start as 2015-06 and primary completion as 2015-11.

Enrollment was 44. The posted arm summaries list 22 participants in the resveratrol group and 22 in the placebo group. The randomization method, sequence generation, and allocation concealment are not reported in the registry record. The record says triple masking, but does not specify which groups of people were masked or how masking was maintained.

Both groups took a monophasic contraceptive pill continuously for 42 days. The placebo group also took starch placebo, while the resveratrol group took 40mg of resveratrol. The brief summary identifies the pill as levonorgestrel 0.15mg and ethinyl estradiol 0.03mg. As a result, the randomized contrast concerns resveratrol added to the pill regimen rather than the pill itself.

The primary endpoint was pain measured by visual analog scale at day 42, with the measurement considering the last 7 days. The primary summary statistic was the median, accompanied by the full range. The registry reports a Mann-Whitney test for the comparison. Further details of the analysis protocol, including any adjustments or prespecified handling of multiple outcomes, are not reported in the registry record.

The stated primary analysis population was intention to treat. The registry describes carrying forward each patient's last recorded pain value or plasma-level measurement at following consultations when follow-up was missed. It does not report how many participants missed follow-up, whether all randomized participants contributed to the primary endpoint, or whether other analysis populations were used.

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

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Intention to treat analysis, patients who were lost on follow-up had their last registry on pain values or plasma levels measurements repeated in the following consultations.

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 Pain Scores Measured by VAS (Visual Analog Scale) at Day 42., measured over 42 days.

The primary endpoint was pain measured with a visual analog scale at day 42. The registry says the assessment considered pain during the last 7 days. The scale runs from 0, meaning no pain, to 10, meaning worst imaginable pain. These anchors give the score a direct interpretation as a self-reported measure of pain intensity.

The endpoint is useful for comparing reported pain between the randomized groups at the specified assessment time. A continuous scale can capture differences across a range of pain experiences rather than reducing the outcome to a simple yes-or-no category. The registry's main summary is the median score in each group, with the full range describing the lowest and highest observed values. This provides information about the center and extent of the reported scores, but not about their full distribution.

In general, pain ratings are patient-reported outcomes: their meaning depends on how participants understand and use the scale, and on consistent timing and instructions. The registry describes the scale anchors and assessment window, but does not report additional details about administration or whether the same procedures were used for every participant.

The primary endpoint is not a measure of pain over the entire treatment period. It is the day-42 assessment focused on the last 7 days. The brief summary describes the endpoint as occurring at the end of 2 months, whereas the endpoint and arm descriptions specify 42 days. The registry record does not reconcile those descriptions.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary comparison uses two different kinds of statistical summaries: medians with full ranges to describe the groups, and a Mann-Whitney test to compare them. These methods answer related but non-identical questions. The medians identify the midpoint of the observed scores when ordered; the full range gives the observed minimum and maximum. The Mann-Whitney test uses the ordering of individual observations rather than comparing only the two reported medians.

What does the median describe?

In general, the median is the central value after observations are ordered. It is less affected by an unusually high or low observation than the arithmetic mean. That can make it a useful summary when measurements are skewed or when a small number of extreme observations might pull the mean. Here, the registry reports medians of 3.2 for resveratrol and 3.9 for placebo.

A median does not describe all participants' scores. Different distributions can share the same median, and the median alone does not show how tightly observations cluster around it. The full range adds the lowest and highest observed scores but not the frequency of values between those extremes. The registry does not provide a quartile-based summary, a distribution plot, or individual observations in the registry record used for this account.

What does the Mann-Whitney test compare?

In general, the Mann-Whitney test is a rank-based method for comparing observations from two independent groups. It orders the combined observations and evaluates whether values from one group tend to rank higher or lower than values from the other. It does not, without further assumptions, test only whether the medians differ. Its interpretation can depend on the shapes and spreads of the group distributions as well as on shifts in their location.

The registry reports a Mann-Whitney test and p = 0.7 for the primary comparison. A p-value is calculated under a null model and summarizes how unusual the observed test result would be if that model held. It is not an estimate of the size of a difference. Since the registry does not report the test statistic, a confidence interval, or individual scores, the reported p-value cannot convey the range of plausible effect sizes on its own.

Why does a confidence interval matter?

In general, a confidence interval describes uncertainty around an estimated quantity, such as a difference between groups. It can communicate both the direction and precision of an estimate, which a p-value alone cannot do. The registry does not report a confidence interval for the primary comparison. Without one, readers have limited information about which effect sizes are compatible with the observed data under a specified method.

The arm summaries are medians and ranges, not the individual ranks used by the Mann-Whitney test. As a general statistical point, those summaries do not determine the rank ordering of all observations. A rank-based test result cannot be reconstructed from the medians and ranges alone. The registry's reported test is therefore the available inferential result, rather than a result that can be independently reproduced from these summaries.

How should a planning illustration be read?

In general, a sample-size calculation describes how many participants a future study might plan for under specified assumptions. It is not a measure of the power actually achieved by a completed trial. The registry's planning assumptions describe a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. They also describe detecting a stated fraction of the observed effect. Those assumptions define a planning exercise, not a result about the trial's observed ability to detect an effect.

Such illustrations depend on the effect chosen for planning and on the calculation assumptions. If the observed effect is used as the starting point, the illustration remains conditional on that estimate and should not be read as an independently established treatment effect. A planning illustration is not observed power, and the registry does not report the trial's own sample-size justification in the registry record for this account.

Finally, the endpoint is a bounded patient-reported scale, and the primary summary is a median. The selection of a rank-based test is consistent with comparing ordered observations, but the record does not report the full statistical analysis plan or diagnostic checks. Those missing details prevent a more complete assessment of assumptions, precision, and analytic choices. Statistical interpretation should therefore stay close to what is actually reported: group medians and ranges, and the Mann-Whitney p-value.

10. Analyses Reported by the Sponsor

The registry reports the sponsor's primary comparison as a Mann-Whitney test, with p = 0.7. The arm summaries are medians and full ranges: 3.2, with a range from 0.0 to 8.0, for resveratrol; and 3.9, with a range from 0.0 to 8.9, for placebo. No confidence interval for the comparison is reported.

The registry record does not flag a discrepancy between a sponsor analysis and a recalculated result. The available group summaries are not enough to reconstruct the Mann-Whitney test independently: in general, that test depends on the ranks of individual observations, which are not determined by medians and ranges. The reported sponsor test is therefore the inferential comparison available in the registry record. The summary statistics alone should not be treated as a substitute for that test or as evidence that its result has been reproduced.

The record does not report further details such as the test statistic, a confidence interval, or an adjusted analysis. Those omissions limit the additional checks that can be made from the posted information. The sponsor's p-value should be interpreted as a test result, not as an estimate of the magnitude or precision of a group difference.

11. Multiplicity, Missing Data and Analysis Populations

The registry lists three outcome measures and three analyses. It identifies pain scores at day 42 as the primary endpoint and lists serum CA125 levels and serum prolactin levels at 42 days as secondary outcomes. Results sufficient to describe the secondary comparisons are not reported in the registry record. The record does not explain whether the listed analyses correspond one-to-one with the outcome measures or whether any other comparisons were conducted.

Multiplicity arises when several outcomes, time points, or statistical tests are considered. In general, conducting more tests can increase the chance of obtaining at least one result that appears notable by chance. A prespecified strategy may address this, for example by defining a primary endpoint or adjusting interpretation across tests. The registry record does not report a multiplicity plan, an adjustment method, or whether secondary outcomes were treated as exploratory. No adjustment should be assumed.

The record describes an intention-to-treat analysis and states that patients lost on follow-up had their last registry value for pain or plasma-level measurements repeated in following consultations. This description indicates a carry-forward approach, but details about the exact implementation are not reported. The number of participants with missing values, the timing of missingness, and the number of values carried forward are also not reported in the registry record.

In general, carrying a last observation forward treats that earlier measurement as the value at a later assessment. This can simplify analysis, but it relies on assumptions about what would have happened after the last recorded measurement. If missingness is related to participants' outcomes, the resulting group summaries may not reflect the outcomes that would have been observed with complete follow-up. The registry does not report sensitivity analyses or alternative missing-data methods, so the effect of its stated procedure cannot be assessed from the record.

The record does not report a detailed statistical analysis plan, the number included in each endpoint analysis, or the handling of protocol deviations. The intention-to-treat label and the stated carry-forward procedure are useful context, but they do not resolve these unanswered questions about analysis populations and missing data.

12. 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 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry reports serious adverse events for 22 participants at risk in each group and 0 participants affected in each group. It lists no serious adverse-event terms. Death counts are not reported in the registry record. These entries describe the posted serious-event information; they should not be taken to mean that every possible safety outcome was assessed or reported in the same way.

The record separately lists other adverse events. In the placebo group, 10 participants were affected among 22 at risk; in the resveratrol group, 13 were affected among 22 at risk. These are counts for the registry's “other” category, distinct from the serious adverse-event counts. The record does not provide the event terms or further detail needed to characterize those events.

In general, adverse-event counts are descriptive. They do not by themselves establish that an intervention caused an event or that no risk exists. Interpretation depends on event definitions, ascertainment, follow-up, and the completeness of reporting. Further information about these methods is not reported in the registry record. The serious-event figures should therefore be read as the counts entered in the registry, not as a comprehensive safety conclusion.

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

The posted primary results describe pain scores at day 42 among participants assigned to resveratrol with a monophasic contraceptive pill or placebo with the same pill. The median was 3.2 in the resveratrol group and 3.9 in the placebo group; the reported Mann-Whitney test had p = 0.7. Those figures convey the reported group summaries and test result, but not a precise estimate of the size of a group contrast.

There is no confidence interval for the primary comparison in the registry record. The summaries do not provide the individual scores or their distributions. It is therefore not possible from the reported medians and ranges alone to assess the precision of a contrast or to determine which values within the distributions contributed to the rank-based test. The p-value is not a probability that the treatment has no effect and does not establish equivalence between groups.

The trial's question was specific: whether adding daily 40mg resveratrol to the stated contraceptive-pill regimen was associated with a difference in pain scores at day 42 compared with adding starch placebo. The findings do not compare resveratrol without the pill, do not compare the pill with no pill, and do not describe outcomes beyond the reported treatment and assessment period.

The registry reports that the primary analysis was intention to treat, alongside a last-recorded-value procedure for missed follow-up. It does not report missing-outcome counts, a detailed analysis plan, or the results of the listed secondary outcomes. Those gaps limit evaluation of the completeness and robustness of the findings.

In general, a clinical trial result is best understood through its estimate, uncertainty, design, and outcome reporting together. Here, the available primary result is a pair of medians and ranges plus a sponsor-reported rank-based p-value. It supports a careful description of what was posted, but not a broad claim about effects in other populations, treatment settings, or follow-up periods.

14. Why This Trial Matters Statistically

This trial illustrates why the summary statistic and the comparison test need to be read together. The posted endpoint summaries are medians with full ranges, while the reported Mann-Whitney test uses the ordering of individual observations. The p-value cannot be inferred from the medians and ranges alone, and the medians do not reveal all features of the distributions. Statistical interpretation depends on understanding what each reported quantity represents.

It also shows the distinction between a test result and an effect estimate with uncertainty. The registry reports p = 0.7, but does not report a confidence interval for the primary comparison. In general, p-values and confidence intervals answer different questions: a test evaluates compatibility with a null model, while an interval conveys uncertainty about an estimated quantity. Without an interval or individual data, the precision of the group contrast is difficult to judge.

The record also makes the analysis population and missing-data approach relevant to interpretation. It labels the primary analysis intention to treat and describes carrying the last recorded values forward after missed follow-up. Since the number and pattern of missing observations are not reported, readers cannot assess how much that procedure affected the result.

Finally, multiple outcome measures are listed, but the record does not report how the analyses were prioritized or whether multiplicity was addressed. This trial is therefore a useful example of the limits of registry summaries: they can document the design and headline results, while leaving important information about precision, missingness, and analytic planning unavailable.

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 posted information has important limits for interpreting the primary result. The primary outcome is summarized by group medians and full ranges, but no confidence interval for a contrast is reported. The record also does not provide the individual pain scores, a fuller distributional summary, or the Mann-Whitney test statistic. These omissions limit assessment of the magnitude and precision of the comparison.

The registry describes randomization and triple masking, but does not report how the random sequence was generated, how allocation was concealed, or which people were masked. It does not give detailed eligibility criteria or report the statistical analysis plan. These details would help readers assess the conduct of the trial and whether the reported analysis followed prespecified methods.

The primary analysis is described as intention to treat, with the last recorded pain or plasma-level value repeated in following consultations for patients lost on follow-up. Missing-outcome counts and sensitivity analyses are not reported. The record therefore does not show how often this procedure was used or how conclusions might change under alternative assumptions about missing values.

Three outcome measures and three analyses are listed, including secondary CA125 and prolactin outcomes, but their results and any multiplicity strategy are not reported in the registry record. The brief summary describes the endpoint at the end of 2 months, while the endpoint and arm descriptions specify 42 days; this difference is not explained. The report also does not give further context for the “other” adverse-event counts or death counts. These limitations are specific to the available record and restrict how fully the trial can be appraised.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Resveratrol for Pain Due to Endometriosis — NCT02475564.
• Registry record last updated 2016-10-14; status last verified 2016-08.
• Results first posted 2016-08-05.
• 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 completed phase 4 study was randomized, triple-masked, and parallel-group, with an enrollment of 44. It compared daily resveratrol at 40mg plus a monophasic contraceptive pill with starch placebo plus the same pill, taken continuously for 42 days. The primary endpoint was pain measured by visual analog scale at day 42, considering the last 7 days.

The reported median pain scores were 3.2 in the resveratrol group and 3.9 in the placebo group. The registry reports a Mann-Whitney test with p = 0.7 and does not report a confidence interval for the comparison. Secondary outcomes were serum CA125 and serum prolactin levels at 42 days, but their results are not reported in the registry record. The record describes an intention-to-treat analysis and a last-recorded-value procedure for missed follow-up, without reporting missing-outcome counts.