Transversus Abdominis Plane Blocks for Patients Undergoing Robotic Gynecologic Oncology Surgery: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Transversus Abdominis Plane Blocks for Patients Undergoing Robotic Gynecologic Oncology Surgery (NCT01444924), a randomized phase 2 study. The primary outcome is 24 Hour Post Operative Opioid Consumption, Converted to Intravenous Morphine Equivalents.

2. Clinical Question

The trial focused on post-operative analgesia in patients having robotic gynecologic oncology surgery. Its primary outcome was not a pain rating: it was opioid consumption over a specified period, expressed in a common unit. Pain scores were listed as a secondary outcome.

The statistical comparison concerns the group means recorded for the primary outcome. It does not, by itself, describe every patient’s experience, pain scores, or other aspects of recovery. The registry record does not report an analysis of the secondary pain-score outcome, nor does it give further detail about the population included in the primary outcome summaries.

3. Trial Design

This was a prospective randomized, placebo-controlled trial with a parallel-group design. The registry lists the study as Phase 2 and reports enrollment of 75. It identifies the sponsor as University of Wisconsin, Madison, and the study status as completed. The recorded start was 2011-09, and primary completion was 2013-02.

Participants were assigned to a pre-operative TAP block with bupivicaine and epinephrine or to a pre-operative TAP block with placebo. The registry’s brief description calls the study single-center and double-blind. Its masking field specifies quadruple masking. The registry record does not explain how those masking descriptions relate to one another or identify which roles were masked.

The primary outcome was 24-hour post-operative opioid consumption converted to intravenous morphine equivalents, reported as a mean in mg with standard deviations. The outcome summaries list 31 participants for the bupivicaine group and 33 for the placebo group. The registry reports enrollment of 75, but the reason the outcome-summary counts differ from that enrollment figure is not reported in the registry record.

Pain scores were listed as a secondary outcome. The registry lists two outcome measures and one posted secondary outcome, but it does not provide a detailed schedule or analysis description for pain scores. The registry records zero posted analyses. The comparison discussed for the primary outcome is an unadjusted recalculation from the posted group summaries, not a reported model-based analysis.

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: A total of 75 patients agreed to participate in the study. Eight patients did not meet inclusion criteria for the study, 2 patients were excluded from the analysis secondary to intraoperative conversion to laparotomy, and 1 additional patient was excluded because the robot was unavailable. This left a total of 64 subjects who completed the study.

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.

Population: The treatment group, who received TAP block placement, was younger than the saline injection group, on average (55.2 versus 62.1, P = 0.028).

6. Primary Endpoint

The registry lists the primary outcome as 24 Hour Post Operative Opioid Consumption, Converted to Intravenous Morphine Equivalents, measured over 24 hours.

The primary endpoint measures the amount of opioid medication consumed in the first 24 hours after surgery, converted to intravenous morphine equivalents and expressed in mg. Conversion to a common opioid-equivalent scale allows the outcome to be summarized using one unit when consumption is represented in that form. The registry reports this continuous outcome as a group mean and standard deviation.

Opioid consumption is used as a measure related to post-operative analgesia. It captures medication use during a defined time window, rather than directly measuring pain intensity. The registry separately lists pain scores as a secondary outcome, so the primary endpoint and that secondary outcome represent different kinds of information.

A mean describes the group’s average, while the standard deviation describes how spread out individual observations are around that average. Neither statistic gives the full distribution of consumption or shows how outcomes varied for each participant. The registry record does not report additional endpoint details such as the exact collection method, handling of missing observations, or the population included in the summaries.

7. Results Posted in the Registry

• Bupivicaine: mean 64.90 versus 69.30 on control; difference -4.40 (95% CI -19.45 to 10.65), standardized effect d = -0.14; z-test p = 0.567.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: each recorded value represents opioid consumption converted to intravenous morphine equivalents, measured in mg. A common summary for a continuous outcome is the mean, accompanied by a standard deviation. The mean locates the group average; the standard deviation describes the spread of observations around that average. These summaries help compare groups, but they do not show the shape of the data or how many individuals had values near particular points.

What does the mean difference represent?

The comparison subtracts the placebo group mean from the bupivicaine group mean. The recalculated mean difference is -4.4 mg. A negative value indicates that the bupivicaine group’s observed mean was lower than the placebo group’s observed mean, using that subtraction order. This is a difference between group averages, not a statement that every participant in one group used less medication than every participant in the other.

The mean difference retains the endpoint’s unit, mg. This makes it possible to interpret the estimate on the same scale as the outcome. The result does not, however, convey whether a difference would matter clinically; that judgment requires a meaningful threshold or context, which is not reported in the registry record.

What does the confidence interval add?

A confidence interval expresses uncertainty around an estimated quantity under the assumptions of the method used to construct it. Here, the 95% confidence interval for the recalculated mean difference runs from -19.45 to 10.65 mg. Its span indicates that the estimate is not highly precise. Because the interval includes zero and values on both sides of zero, the posted summaries do not pin down the direction of the underlying mean difference.

A confidence interval is not a range containing a known fraction of individual outcomes. It also does not assign a probability to the true difference after the data have been observed. It is a statistical tool for showing the range of values compatible with the data and the calculation’s assumptions.

How should the p-value be read?

The unadjusted recalculated p-value is 0.567. In general, a p-value measures how compatible the observed test result is with a null hypothesis under a specified statistical model. It does not state the probability that the null hypothesis is true, the probability that chance alone caused the observed data, or the probability that the result will repeat. A p-value should be considered alongside the effect estimate, confidence interval, study design, and analysis limitations.

The comparison is an unadjusted recalculation from the posted group summaries. The registry record lists zero posted analyses, so a sponsor-reported inferential analysis for the primary outcome is not reported in the registry record. The comparison should not be mistaken for an adjusted analysis or a model using participant-level data.

Why do the standard deviations matter?

The standard deviations are 28.65 mg in the bupivicaine group and 32.73 mg in the placebo group. They describe variation among recorded outcome values and help convey that group averages do not represent all participants. In a general statistical comparison of means, the estimated uncertainty depends on both the spread of the data and the amount of information available. Greater variability can make a group difference harder to estimate precisely.

These summaries do not establish whether the outcome distributions were approximately normal, whether there were unusually high values, or whether another analysis would be preferable. Distributional details and diagnostic checks are not reported in the registry record. The calculation uses the posted means, standard deviations, and group counts; it cannot account for features of the individual observations that are absent from those summaries.

What does randomization contribute?

Random allocation is intended to make the assigned groups comparable on average, including for factors that are not measured. A placebo comparator can help separate differences associated with assignment from differences associated with receiving no study procedure, depending on how the trial was conducted. These design features do not eliminate uncertainty from the outcome data, missing observations, or trial conduct. The registry record does not report allocation procedures or detailed masking procedures beyond its design descriptions.

The record calls the study double-blind in its brief description and lists quadruple masking in its masking field. It does not clarify the exact roles included in either description. The record also does not report the original statistical plan, prespecified adjustment methods, or the analysis population used for the posted summaries. Those omissions limit how fully the recalculated comparison can be connected to the trial’s planned analysis.

10. Confidence Intervals and Precision

The 95% confidence interval for the unadjusted recalculated mean difference is -19.45 to 10.65 mg. It is centered on the estimated difference of -4.4 mg, but extends from a value favoring lower mean consumption in the bupivicaine group to a value favoring lower mean consumption in the placebo group. The interval therefore leaves substantial uncertainty about both the magnitude and direction of the underlying difference.

In general, a confidence interval combines the estimated effect with its statistical uncertainty. A narrower interval indicates greater precision for the quantity being estimated; a wider interval indicates less precision. Precision is distinct from whether an effect is clinically important. The registry record does not state a threshold for a clinically meaningful difference, so the interval cannot be classified against such a threshold.

The unadjusted p-value is 0.567, consistent with the confidence interval including zero under the corresponding comparison. Neither statistic proves that the groups are the same. The data summarized in the registry are compatible with a range of possible mean differences, and the point estimate should be interpreted in light of that uncertainty.

The interval is a recalculation from group summaries, not a confidence interval from a sponsor-reported analysis in the registry record. The record does not report participant-level data, missing-data handling, or additional modeling details that might affect an analysis. Those limitations matter when interpreting precision: the interval conveys uncertainty under its calculation, but cannot resolve uncertainty arising from unreported design or data features.

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, not the trial’s own design calculation. The listed assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each row uses the stated fraction of the observed effect as the effect to detect. The trial’s original sample-size assumptions are not reported in the registry record.

For an effect equal to 100% of the observed effect, the illustration gives 771 participants per arm for 80% power and 1,032 participants per arm for 90% power. Planning for 75% of the observed effect gives 1,370 participants per arm for 80% power and 1,834 participants per arm for 90% power. Planning for 50% of the observed effect gives 3,082 participants per arm for 80% power and 4,126 participants per arm for 90% power.

Power is the probability, under the stated assumptions and for the effect being planned for, of detecting that effect using the specified test. The 80% and 90% columns represent different power targets: the higher target requires more participants in these illustrations. Smaller effects are harder to distinguish from random variation, so planning to detect a smaller fraction of the observed effect requires more participants.

These figures are not observed power. They are planning illustrations based on a recalculated effect and stated assumptions; they do not describe the probability that this completed trial detected an effect, nor do they show the trial’s original design target. The visual presentation of the planning values should be read in the same way: as an illustration of how assumed effect size and desired power relate to participants per arm.

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 = -4.400; pooled standard deviation σ = 30.823.
2. n = 2 × (1.96 + 0.842)² × 30.823² / -4.400² = 770.4, rounded up to 771 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 <- -4.39999999999999                      # observed difference in means
sigma <- 30.8233174723293                     # 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(1444924)
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 = 771 (80% power), 1,032 (90% power)
 75% of observed effect: n per arm = 1,370 (80% power), 1,834 (90% power)
 50% of observed effect: n per arm = 3,082 (80% power), 4,126 (90% power)
power.t.test: 771.3 
Simulated power at n = 771 per arm: 0.796 (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. Multiplicity, Missing Data and Analysis Populations

The registry lists two outcome measures and identifies one secondary outcome, pain scores. The primary outcome is 24-hour post-operative opioid consumption converted to intravenous morphine equivalents. The registry record does not report results for the secondary pain-score outcome, the number of pain-score time points, or a detailed outcome hierarchy beyond the designation of the primary endpoint.

Multiplicity arises when several outcomes, time points, or comparisons are tested. In general, conducting more tests can increase the chance that at least one appears statistically notable by chance. Statistical plans may address this through prespecified prioritization or adjustments, but the registry record does not report whether any multiplicity strategy was planned or used. The unadjusted p-value for the recalculated primary comparison should not be interpreted as accounting for other outcomes or analyses.

The registry records zero posted analyses. It does not report a full statistical analysis plan, the exact test used by the sponsor, covariate adjustment, or a primary analysis population such as intention-to-treat or per-protocol. The comparison discussed is an unadjusted recalculation from group-level summaries; it is not evidence that a particular prespecified sponsor analysis was performed.

Missing-data handling is not reported in the registry record. The record gives an enrollment figure of 75 and outcome-summary counts of 31 for bupivicaine and 33 for placebo, but it does not explain the relationship between those figures. It does not state whether all randomized participants contributed outcome data, why any observations might be absent, or whether missing outcomes were imputed or otherwise addressed. Without that information, the potential influence of missingness on the comparison cannot be assessed.

The record also does not report exclusions after randomization, adherence to assigned procedures, protocol deviations, or whether the analysis followed original assignment. These are important details for evaluating how closely the summarized groups reflect the randomized comparison. Their absence should be treated as uncertainty about the analysis, not as evidence that a specific problem occurred.

14. 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.

The adverse-event entries list 31 participants at risk for serious adverse events in the bupivicaine group and 33 in the placebo group. The number recorded as affected by a serious adverse event is 0 in each group. The entries also list 31 and 33 at risk for other adverse events, respectively, with 0 recorded as affected in each group.

These counts describe what the registry record reports; they do not establish that no adverse events occurred outside the record’s reporting scope or that the groups have identical safety profiles. A zero count is also not, by itself, proof that an event is impossible. The registry does not provide event-term details for these entries, and its list of top serious-event terms is empty.

Deaths are not reported in the registry record. The adverse-event figures should be read as recorded counts for the listed groups, not as a complete account of every possible safety outcome or as a causal assessment of the intervention.

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

The primary comparison estimates the difference in mean 24-hour opioid consumption, converted to intravenous morphine equivalents, between the bupivicaine and placebo groups. The recalculated estimate is -4.4 mg, with a 95% confidence interval from -19.45 to 10.65 mg and an unadjusted p-value of 0.567. The interval includes zero and spans values in both directions, so the posted summary data leave uncertainty about the size and direction of the underlying mean difference.

This result does not establish that the groups are equivalent or that there is no effect. Demonstrating equivalence would require an appropriate prespecified margin and analysis, neither of which is reported in the registry record. Nor does the estimate establish that any possible difference is clinically important. The record does not give a threshold for meaningful change in opioid consumption.

The endpoint is medication consumption, not a direct measure of pain intensity. Pain scores are listed as a secondary outcome, but their results are not reported in the registry record. The primary comparison therefore cannot answer what the pain-score outcome showed, and it does not summarize every aspect of post-operative recovery.

The result also does not establish how the findings would apply beyond the studied setting. The record describes a single-center trial in patients undergoing robotic surgery for gynecologic cancers. Additional details about the setting, participant characteristics, or the analysis population are not reported in the registry record. The available summaries do not show individual outcomes or explain the difference between the enrollment figure and the outcome-summary counts.

The most defensible interpretation is that the posted group summaries yield an uncertain estimate of the mean difference. Randomization and placebo control are relevant design features, but the registry record does not report enough information about the planned analysis, missing data, or masking procedures to resolve all questions about the comparison. The figures should be interpreted as statistical evidence about this specific outcome and record, not as a broad conclusion about treatment effects.

16. Why This Trial Matters Statistically

This trial illustrates how the choice of endpoint shapes the statistical question. The primary outcome is a continuous measure of opioid consumption during a defined post-operative period, while pain scores are listed separately as a secondary outcome. These outcomes capture different information. A comparison of average consumption cannot stand in for a comparison of pain scores, and a group mean does not describe each participant’s experience.

The result also shows why an effect estimate should be read with its uncertainty. The recalculated mean difference is -4.4 mg, but its confidence interval extends from -19.45 to 10.65 mg. Considering the point estimate alone would hide how broadly the underlying difference remains uncertain. The unadjusted p-value of 0.567 does not tell readers whether the estimate is clinically important or whether the groups are equivalent.

Sample-size planning depends on the effect a study aims to detect and the desired power. The planning illustrations demonstrate that smaller target effects require more participants per arm under the stated assumptions. They are separate from the original design calculation, which is not reported in the registry record, and they are not a measure of the completed trial’s observed power.

Finally, the registry record makes visible the distinction between reported group summaries and a full statistical analysis. The record contains outcome means and standard deviations from which an unadjusted comparison can be recalculated, but it lists zero posted analyses and does not describe missing-data handling or the analysis population. Recognizing what is reported—and what is not—helps prevent an apparently simple group comparison from being given more certainty than its documentation supports.

17. 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 comparison is recalculated from group-level means, standard deviations, and counts. Participant-level observations and a sponsor-reported analysis are not reported in the registry record, so the calculation cannot account for the outcome distribution, covariates, or analysis choices that might be relevant in a full analysis.

The registry reports enrollment of 75, while the primary outcome summaries list 31 participants in the bupivicaine group and 33 in the placebo group. The record does not explain why those figures differ or describe how missing observations were handled. The analysis population and any exclusions after randomization are not reported in the registry record.

The registry describes masking as double-blind in the brief study description and lists quadruple masking in the design field. It does not clarify the roles included in those descriptions. Allocation procedures, adherence, protocol deviations, and the original statistical plan are also not reported. These omissions limit assessment of how the trial was implemented and how the posted comparison relates to its intended analysis.

The setting is described as single-center, and the study concerns robotic surgery for gynecologic cancers. The registry record does not report enough detail about participant characteristics or the care setting to assess how broadly the findings may apply. It also does not report the secondary pain-score results, despite listing pain scores as an outcome.

Finally, the confidence interval is wide enough to leave substantial uncertainty about the mean difference. No clinical importance threshold is reported, and the record does not provide information to assess the relevance of every value within the interval. These limitations do not show that the result is biased; they identify what cannot be evaluated from the registry information.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Transversus Abdominis Plane Blocks for Patients Undergoing Robotic Gynecologic Oncology Surgery — NCT01444924.
• Registry record last updated 2019-11-27; status last verified 2018-03.
• Results first posted 2014-09-23.
• 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.

21. Record Summary

NCT01444924 is a completed Phase 2 randomized, parallel-group, placebo-controlled trial of pre-operative TAP blocks for patients undergoing robotic gynecologic oncology surgery. The registry describes the study as single-center and double-blind, while its masking field lists quadruple masking. Enrollment was 75.

The primary outcome was mean 24-hour post-operative opioid consumption converted to intravenous morphine equivalents, measured in mg. The posted means were 64.9 mg for bupivicaine and 69.3 mg for placebo. The unadjusted recalculated difference was -4.4 mg, with a 95% confidence interval from -19.45 to 10.65 mg and an unadjusted p-value of 0.567. Pain scores were listed as a secondary outcome, but their results are not reported in the registry record.

The registry lists zero posted analyses. Missing-data methods, the analysis population, and the original sample-size assumptions are not reported in the registry record. The planning figures are illustrations based on the observed effect and stated assumptions, not the trial’s original design calculation.