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 Transversus Abdominis Plane (TAP) Block Laparoscopic Hysterectomy (NCT01074229), a randomized na study. The primary outcome is QoR40 on the Day After Surgery.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01074229 |
| Phase | NA |
| Condition | Postoperative Pain |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Triple |
| Enrollment | 75 |
| Arms in the primary outcome | 3 |
| Lead sponsor | Northwestern University |
| Results posted | Yes |
2. Clinical Question
Population
Patients undergoing laparoscopic hysterectomy. The registry record lists postoperative pain as the condition and records enrollment of 75, but does not report further eligibility details or a fuller description of the analyzed population.
Intervention
A pre-operative transversus abdominis plane (TAP) block using ropivacaine. The registry lists arms receiving 20 cc of 0.5% ropivacaine and 20 cc of 0.25% ropivacaine.
Comparator
Placebo, described in the registry as sterile normal saline. The record describes a parallel-group randomized study with triple masking.
Primary question
How did quality-of-recovery scores on the day after surgery compare among the placebo group and the two ropivacaine groups? The registry reports the outcome as QoR40, a score ranging from 40 to 200, with higher scores described as better recovery.
3. Trial Design
The registry describes a prospective, randomized, blinded study of pre-operative TAP block in patients undergoing laparoscopic hysterectomy. Allocation was randomized, masking was listed as triple, and the model was parallel. The record lists 75 participants enrolled and marks the study completed. It records a start of 2010-03 and primary completion of 2010-10.
Three groups are reported for the primary outcome: placebo, 20 cc of 0.5% ropivacaine, and 20 cc of 0.25% ropivacaine. The placebo is described as sterile normal saline; the active interventions are described as instillation of the stated ropivacaine solutions. The outcome-specific group counts are 23, 22, and 21, respectively. The registry record does not explain how those counts relate to the enrollment total, or describe exclusions from the outcome analysis.
The primary endpoint was QoR40 on the day after surgery. The posted outcome summaries use medians and inter-quartile ranges. The registry also lists total morphine consumption over one day as a secondary outcome, with means and standard deviations. The sponsor is Northwestern University. The study phase is recorded as not applicable.
Further details about the randomization procedure, concealment, masking roles, protocol deviations, and analysis population are not reported in the registry record. The record does not report a detailed protocol or a sample-size justification. The listed enrollment should therefore be read as the registry's enrollment figure, not as proof that every enrolled participant contributed to each posted outcome.
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 | Placebo | 20 cc of 0.5% Ropivacaine | 20 cc of 0.25% Ropivacaine |
|---|---|---|---|
| STARTED | 25 | 25 | 25 |
| COMPLETED | 23 | 22 | 21 |
| NOT COMPLETED | 2 | 3 | 4 |
Reasons for not completing this period:
| Reason | Placebo | 20 cc of 0.5% Ropivacaine | 20 cc of 0.25% Ropivacaine |
|---|---|---|---|
| Lost to Follow-up | 1 | 0 | 0 |
| Change to open surgical procedure | 1 | 3 | 4 |
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 | Placebo | Study Drug | 20 cc of 0.25% Ropivacaine | Total |
|---|---|---|---|---|---|
| Participants analysed | 25 | 25 | 25 | 75 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 25 | 25 | 25 | 75 |
| Age, Categorical: >=65 years | Participants | 0 | 0 | 0 | 0 |
| Age, Continuous | years | 47.4 (SD 9.6) | 45.4 (SD 4.5) | 46.76 (SD 6.4) | 46.55 (SD 7.2) |
| Sex: Female, Male: Female | Participants | 25 | 25 | 25 | 75 |
| Sex: Female, Male: Male | Participants | 0 | 0 | 0 | 0 |
| Region of Enrollment: United States | participants | 25 | 25 | 25 | 75 |
6. Primary Endpoint
The registry lists the primary outcome as QoR40 on the Day After Surgery, measured over 1 day.
| Element | Registry entry |
|---|---|
| Result type | Median |
| Measure of spread | Inter-Quartile Range |
| Unit | units on a scale |
| Endpoint classification | not reduced to a single comparison |
The primary outcome is QoR40 on the day after surgery. The registry describes it as a score from 40 to 200, with 40 representing poor recovery and 200 representing good recovery. A recovery questionnaire can capture a broader patient-reported experience than a single symptom or medication-use measure. In this trial, the outcome is intended to describe quality of recovery after laparoscopic hysterectomy.
The registry reports the outcome as a median and inter-quartile range for each group. The median represents the middle of the observed values when ordered; the inter-quartile range describes the central spread of those values. These summaries are useful when an outcome is analyzed with a rank-based method, as in the registry's reported Kruskal-Wallis and Dunn tests. They do not reveal every individual score or the full shape of each group's distribution.
The recorded time point is one day after surgery. The registry does not report details about questionnaire completion, missing responses, or how a score was handled if some items were absent. It also does not report a threshold for a clinically important difference. Consequently, the numerical contrast and its uncertainty can be described, but the record alone does not establish how patients would experience a given score difference.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The posted primary outcome summaries place both ropivacaine groups at a median QoR40 score of 180. The placebo group's median is 152. The inter-quartile ranges are 169 to 190 for 20 cc of 0.5% ropivacaine, 161 to 184 for 20 cc of 0.25% ropivacaine, and 136 to 167 for placebo. These are group summaries, not individual outcomes, and the overlap or separation of inter-quartile ranges is not a substitute for a formal comparison.
The registry reports an overall Kruskal-Wallis analysis across all three groups with p = .05. It also reports Dunn comparisons of placebo with each ropivacaine group. For placebo versus 20 cc of 0.5% ropivacaine, the reported median difference is 28, with a 95% confidence interval from 9 to 37 and p = .05. For placebo versus 20 cc of 0.25% ropivacaine, the registry labels the reported estimate a mean difference (net) of 28, with a 95% confidence interval from 14 to 42 and p = .05. The different labels for the pairwise estimates matter: the registry does not present these two estimates in fully consistent terms.
A confidence interval describes a range of values compatible with the estimate under the assumptions of the analysis. It conveys uncertainty as well as direction and magnitude. It is not a guarantee that the true value lies within the particular interval, and it does not describe how much individual participants' scores varied. The registry record does not state a clinically important threshold for QoR40, so statistical evidence should not be equated with a specific patient-perceived benefit.
The results are based on the posted outcome counts, which are smaller than the enrollment figure. The registry record does not explain this difference or report how missing outcomes were handled. Nor does it provide enough detail to assess the robustness of the analyses to alternative methods or assumptions. The primary findings should therefore be understood as the posted summaries and reported tests for the participants represented in those summaries, rather than as a complete account of every enrolled participant.
The reported overall and pairwise p-values are close to the conventional .05 threshold, but the record does not describe a prespecified multiplicity strategy. The meaning of these p-values depends on the analysis plan and on how many outcomes and comparisons were considered. In the absence of a reported plan, the values are best read as the results of the tests identified in the registry, not as a complete measure of the strength or clinical importance of the evidence.
9. Statistical Methods Explained
The registry reports a Kruskal-Wallis test for the primary outcome across the placebo and two ropivacaine groups. In general, this is a rank-based method for assessing whether observations across multiple independent groups differ in their distributions. It works with the ordering of observations rather than requiring a comparison of group means. A statistically notable result indicates evidence that the groups do not all have the same distribution under the test assumptions; by itself, it does not identify which groups differ or quantify a particular pairwise contrast. Pairwise follow-up tests address those more specific questions.
What does the Kruskal-Wallis result address?
The registry gives an overall p-value of .05 for the primary outcome. A p-value describes how unusual data at least as incompatible with a null hypothesis would be if that hypothesis and the test assumptions were correct. It is not the probability that the null hypothesis is true, nor is it a measure of the size or clinical importance of an effect. The overall test is distinct from the reported comparisons between placebo and each ropivacaine group.
The record names Dunn tests for the pairwise primary comparisons. In general, Dunn's procedure compares group ranks after a rank-based overall analysis. The registry reports a 95% confidence interval for each pairwise estimate, but it does not give a detailed account of the calculation, the rank summaries, or whether the pairwise tests were adjusted for multiple comparisons. The two pairwise estimates are also described with different labels: one as a median difference and the other as a mean difference (net). That inconsistency limits how confidently the pairwise estimates can be treated as the same type of quantity.
How should the summaries and intervals be read?
The group summaries for QoR40 are medians and inter-quartile ranges. A median is a measure of the center of a distribution that is less affected by extreme values than a mean. The inter-quartile range describes the span from the lower to the upper quartile and gives information about the spread of the middle portion of the observations. It does not show the full distribution, and it is not itself a confidence interval for the median.
A confidence interval gives a range of estimates compatible with the data under the calculation's assumptions. A narrower interval indicates more precision than a wider interval, all else equal. Interpreting an interval also requires knowing what the estimate represents and whether the method is appropriate. The registry does not provide enough detail to reconstruct all aspects of the primary pairwise analysis; the reported estimates and intervals should therefore be read as recorded rather than as independently verified calculations.
What can the secondary calculations add?
The secondary outcome is total morphine consumption over one day, reported by group as means and standard deviations. The posted recalculations compare the placebo mean with each active-group mean using an unadjusted mean difference and confidence interval. These are simple, unadjusted re-calculations from the posted summary statistics, not substitutes for the sponsor's reported analysis. The registry's reported secondary analysis uses an overall Kruskal-Wallis test and a Dunn comparison for placebo versus the 0.5% group. Because the reported rank-based analysis and the recalculated mean comparison do not target precisely the same summary, their estimates and p-values need not match.
For a mean difference, the confidence interval communicates uncertainty around the estimated difference. If an interval includes zero, values corresponding to no difference are compatible with that interval under the calculation. This does not prove there is no effect; it indicates that the posted summary statistics do not precisely distinguish the estimate from zero at the interval's confidence level. The recalculations are unadjusted, so their p-values do not account for testing multiple comparisons or outcomes.
Why do sample-size illustrations differ by assumed effect?
The planning illustrations use fractions of the observed effect and give participants per arm for 80% power and participants per arm for 90% power. They are not the trial's actual design justification and do not describe observed power. In general, a planning calculation asks how many participants might be needed to detect an assumed effect with a chosen significance level and power, given modeling assumptions. A smaller target effect generally requires a larger sample to distinguish it from random variation. Here, the illustrations are explicitly based on the observed effect, equal allocation between two arms, a two-sided significance level of 0.05, and a normal approximation. The registry record does not report that these assumptions were used to plan the trial.
These calculations should be treated as planning examples rather than evidence that the study was adequately or inadequately powered. The record does not report a sample-size justification, the effect size anticipated before enrollment, or a prespecified primary comparison. Post hoc planning illustrations cannot repair that absence, because using an observed estimate as the planning target may not reflect what investigators considered before the study began.
10. Analyses Reported by the Sponsor
| Method | Estimate | 95% CI | P-value |
|---|---|---|---|
| Kruskal-Wallis | not reported | 0.050 | |
| Dunns test | Median Difference (Final Values) 28 | 9 to 37 | 0.050 |
| Dunns Test | Mean Difference (Net) 28 | 14 to 42 | 0.050 |
The sponsor's posted primary analysis uses a Kruskal-Wallis test across all three groups and Dunn tests for placebo comparisons with the two ropivacaine groups. Those reported tests and estimates are the registry's own results. The summary statistics and pairwise estimates should be interpreted alongside the fact that the record labels one pairwise result as a median difference and the other as a mean difference (net).
The secondary outcome also has a sponsor-reported rank-based analysis. The posted recalculations for that outcome instead use unadjusted mean differences based on the group means and standard deviations. These calculations are not a reproduction of the sponsor's Dunn analysis: they use a different summary measure and a different comparison method. Therefore, a difference between the recalculated p-value and the sponsor-reported p-value would not by itself show that either calculation is erroneous. Each answers a related but distinct statistical question.
The registry does not provide the full statistical analysis plan or detailed calculation procedures, so the reported sponsor analyses cannot be independently reconstructed in full from the record. The recalculations are useful as a transparent secondary check on the posted summary statistics, but they do not replace the sponsor's analysis. The registry record does not identify a discrepancy flag for these results.
11. Multiplicity, Missing Data and Analysis Populations
The record reports one primary outcome, three groups, an overall test, and pairwise comparisons of placebo with each ropivacaine group. It also reports a secondary outcome and at least one secondary pairwise analysis. The registry record does not report a prespecified multiplicity plan, such as whether the pairwise comparisons were adjusted, whether the overall test had to precede pairwise testing, or whether the secondary outcome was considered supportive or exploratory.
Multiplicity matters because the chance of at least one apparently unusual result can increase when many hypotheses are tested. The interpretation of an individual p-value depends in part on which tests were planned and how the analysis handled that family of tests. Without the statistical analysis plan, it is not possible to determine from the registry whether the reported p-values were adjusted, whether other analyses were conducted, or how any analysis hierarchy was defined. This uncertainty should temper strong conclusions based on a threshold alone.
Missing-data handling is also not reported in the registry record. The enrollment figure is 75, while the group counts posted for the primary outcome are 23, 22, and 21. The record does not explain why the counts differ, whether outcomes were unavailable, or whether participants were excluded for another reason. It does not state whether analyses followed intention-to-treat, per-protocol, or another population definition.
The record also does not describe how missing questionnaire items or incomplete morphine-consumption data were handled, whether imputation was used, or whether sensitivity analyses were conducted. These omissions matter because analysis populations and missing-data assumptions can affect both estimates and uncertainty. The posted results remain interpretable as summaries for the participants included in those outcomes, but the registry alone does not establish how representative they are of all enrolled participants.
12. 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 |
|---|---|---|---|
| Placebo | 0 | 25 | 0.0% |
| Study Drug | 0 | 25 | 0.0% |
| 20 cc of 0.25% Ropivacaine | 0 | 25 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 5% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Placebo | 0 of 25 |
| Study Drug | 0 of 25 |
| 20 cc of 0.25% Ropivacaine | 0 of 25 |
The registry posts safety group counts of 25 at risk for each of the three listed groups. It records zero participants affected by serious adverse events and zero affected by other adverse events in each group. Death counts are not reported in the registry record. No serious adverse-event terms are listed.
These figures describe what was posted for the registry's safety groups; they do not establish that no adverse events occurred outside the categories or reporting period represented. The safety group labels include Placebo, Study Drug, and 20 cc of 0.25% Ropivacaine. The record does not explain the Study Drug label in further detail or clarify why these at-risk counts differ from the outcome-specific group counts. The adverse-event timeframe and collection procedures are not reported in the registry record.
Zero reported events should be read as a registry count, not as proof that an event is impossible or that all risks have been ruled out. The available record does not provide event-level narratives, severity breakdowns beyond the serious/non-serious categories, or details about monitoring. These limitations restrict what can be concluded from the safety figures alone.
13. What the Result Does, and Does Not, Mean
The registry reports higher primary outcome medians in both ropivacaine groups than in the placebo group, together with an overall rank-based test and pairwise comparisons. These are findings about the posted QoR40 scores at the recorded time point. The associated confidence intervals provide information about the uncertainty around the pairwise estimates, but they do not quantify patient-to-patient variation or define the importance of a difference to patients.
The secondary outcome's broad direction is consistent with lower mean morphine consumption in the active groups, but it is a distinct measure and is not a substitute for the primary endpoint. The registry's secondary analyses and the recalculations use different statistical summaries. Unadjusted secondary results also warrant caution when the multiplicity plan is not reported.
These results do not establish how the intervention would perform in every clinical setting or for all patients undergoing laparoscopic hysterectomy. The registry record does not report enough detail about eligibility, missing outcomes, analysis populations, or the protocol to assess all sources of potential bias. Nor does it report a clinically important threshold for the recovery score. Statistical evidence and clinical importance are related but different questions.
The figures also do not establish that a treatment works or does not work. They describe the observed group summaries and the analyses recorded in the registry. A complete assessment would require the study's full report and protocol details, which are not reported in the registry record. The safety counts likewise represent reported categories and do not demonstrate the absence of all possible harms.
14. Why This Trial Matters Statistically
This trial is statistically instructive because it compares three groups using both an overall rank-based test and pairwise follow-up comparisons. The overall test addresses whether the distributions are alike across groups, while pairwise comparisons ask more specific questions about placebo relative to each active group. Keeping those questions distinct helps avoid treating one overall p-value as a complete description of every group contrast.
The primary summaries are medians and inter-quartile ranges, and the registry names nonparametric methods. That makes it important to distinguish a median or rank-based analysis from a mean-based comparison. The record's inconsistent labels for the two primary pairwise estimates further illustrate why an estimate's definition matters, not just its numerical value or p-value.
The secondary outcome shows another useful distinction: the sponsor's reported rank-based comparison and the recalculated mean differences are not the same analysis. Recalculations from summary statistics can provide a transparent check, but they cannot recreate undocumented choices in the original analysis. Intervals, analysis methods, outcome definitions, and missing-data decisions all contribute to interpretation.
Finally, the registry reports enrollment and outcome-specific group counts without explaining their relationship, and it does not report a multiplicity plan or sample-size justification. These gaps make it difficult to assess the precision and generalizability of the findings fully. They also demonstrate why a p-value alone is not a complete statistical interpretation.
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.
Several limitations are specific to the information recorded for this trial. The registry lists 75 participants enrolled, but the primary outcome summaries include group counts of 23, 22, and 21. It does not explain the difference, state how many participants were analyzed for the secondary outcome beyond its group summaries, or identify the analysis population. The handling of missing outcomes and incomplete questionnaires is not reported in the registry record.
The record describes triple masking but does not specify which groups of people were masked or how masking was maintained. It does not provide the randomization sequence method, allocation concealment details, or information about protocol deviations. Eligibility criteria and participant characteristics are not reported in sufficient detail to assess how broadly the results may apply.
The primary pairwise estimates have inconsistent labels, with one described as a median difference and the other as a mean difference (net). The registry does not include enough detail to resolve this. It also does not report the full statistical analysis plan, multiplicity handling, a prespecified clinically important difference, or a sample-size justification. The planning illustrations based on observed effects are not a substitute for those design details.
The safety record lists no affected participants in the reported adverse-event categories, but does not give the collection timeframe or event-monitoring procedures. Death counts are not reported in the registry record. Finally, only one secondary outcome is posted, so the registry record does not provide a comprehensive account of other possible outcomes or analyses.
16. Related Tutorials
17. Related Statistical Calculators
18. Sources
- ClinicalTrials.gov: Transversus Abdominis Plane (TAP) Block Laparoscopic Hysterectomy — NCT01074229.
- Registry record last updated 2014-05-08; status last verified 2014-04.
- Results first posted 2014-05-08.
- 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
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19. Record Summary
NCT01074229 is a completed, randomized, triple-masked, parallel-group study sponsored by Northwestern University. The registry records 75 enrolled participants and compares placebo with 20 cc of 0.5% ropivacaine and 20 cc of 0.25% ropivacaine in patients undergoing laparoscopic hysterectomy.
The primary outcome is QoR40 on the day after surgery, summarized by group with medians and inter-quartile ranges. The registry reports an overall Kruskal-Wallis test and Dunn pairwise comparisons. Total morphine consumption over one day is the posted secondary outcome. The record also posts adverse-event counts, with zero affected participants in the reported serious and other adverse-event categories; deaths are not reported.
Important details—including missing-data handling, the analysis population, multiplicity procedures, and sample-size justification—are not reported in the registry record. The posted statistics should be interpreted with those limits in mind.