Post-Operative Therapy for Nausea or Vomiting: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Post-Operative Therapy for Nausea or Vomiting (NCT03075163), a randomized phase 4 study. The primary outcome is Change in Nausea Score.

2. Clinical Question

The registry record lists the study as phase 4 and reports a planned enrollment of 300. The posted primary-outcome results include 12 participants in each arm. The record does not explain the difference between the planned enrollment and the numbers with posted outcome results, nor does it report additional participant-level details that would clarify who contributed to the outcome analysis.

The clinical comparison is specifically about a score change over the stated treatment period, not a broad measure of recovery or a long-term outcome. The record does not post a secondary outcome analysis. It also does not state whether participants could receive rescue medication during the measurement period or how such medication use was handled in the analysis. Those details are not reported in the registry record, so the result should be read as an analysis of the posted nausea-score endpoint rather than as evidence about other aspects of postoperative care.

3. Trial Design

The registry record describes a prospective, randomized controlled study conducted at a single site, the University of California, Davis. It was registered as phase 4 and used a parallel-group model: participants were assigned to one of two groups, and the acupressure and ondansetron groups were distinct. The record lists allocation as randomized and masking as none. It does not report how the random sequence was generated or whether allocation was concealed.

The two interventions were acupressure and ondansetron. Acupressure was described as manual pressure applied bilaterally at the wrists. Ondansetron was described as a drug used to treat nausea and vomiting. The study summary characterizes acupressure as an initial treatment before rescue medications. Further procedural details, including how long treatment was applied and the timing or rules for rescue treatment, are not reported in the registry record.

The planned enrollment was 300. Posted primary-outcome results show 12 participants in the acupressure arm and 12 in the ondansetron arm. The registry status is terminated. The record does not state why the study was terminated, how many people were screened or randomized, or whether the posted outcome groups represent everyone enrolled or only participants with available outcome data. It also does not report the trial's original sample-size justification or the assumptions used to plan enrollment.

The study began on 2016-10-18, and primary completion is recorded as 2017-04. These dates describe the registry timeline; they do not, by themselves, explain the duration of treatment or follow-up for an individual participant. No masking was listed, so the record does not indicate that participants, care providers, or outcome assessors were blinded. The role of each group in outcome assessment is not described in further detail.

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:

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Change in Nausea Score, measured over Time to discharge from post anesthetic care unit.

The primary endpoint was titled Change in Nausea Score. It measured the difference between the nausea score before and after treatment, with the assessment timeframe given as time to discharge from the post anesthetic care unit. The score was on a scale from 1 to 10: 1 meant no nausea, while 10 meant severe nausea with impending vomiting. The record states that a greater difference represents a better outcome.

A change score focuses on how a participant's reported nausea differs between two assessments rather than on the score at only one time. In general, change measures can reflect improvement or worsening over the interval, but their interpretation depends on the scoring direction and the definition of the subtraction. The registry description does not give further operational details about how the before-and-after difference was calculated, such as which score was subtracted from which. The stated interpretation—that a greater difference is better—should therefore be retained without adding an unstated scoring convention.

The endpoint was summarized as a mean, with standard error reported as the dispersion measure for each arm. A mean offers a group-level description of the scores, while the standard error describes precision of the estimated mean rather than the spread of individual participants' scores. The record does not report additional primary-outcome details such as a minimally important difference, validation information for this particular use of the scale, or the handling of scores recorded after rescue medication. Those details are not reported in the registry record.

7. Results Posted in the Registry

• Ondansetron: mean 1.25 versus 1.88 on control; difference -0.63 (95% CI -6.67 to 5.41), standardized effect d = -0.08; z-test p = 0.838.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: it is a numerical score change summarized by a mean. The registry reports arm-level means and standard errors, and a mean difference comparing the groups. These summaries answer related but distinct questions. Each arm mean describes its own group, while the mean difference estimates the contrast between groups. The confidence interval describes uncertainty around that contrast, and the p-value summarizes evidence against a null comparison under the test used.

What does the mean difference represent?

The posted group means are 1.88 for acupressure and 1.25 for ondansetron. The reported comparison is a mean difference of -0.63 for ondansetron, with a confidence interval from -6.668 to 5.408. The contrast summarizes the gap between the groups on the recorded change-score scale. A difference of zero would correspond to equal group means under the contrast definition. The registry does not provide a separate adjusted estimate, so the posted result should not be described as adjusted for participant characteristics or other variables.

In general, a mean difference is easy to interpret when the scale and direction are clearly defined. Here, the endpoint description says that a greater before-and-after difference is better, but the record does not provide the subtraction order used to calculate that score. It is therefore important not to assign extra clinical meaning to the sign beyond the contrast as recorded. The score range and the description of its endpoints provide context, but they do not resolve every detail of score construction.

What does the standard error describe?

The posted arm summaries identify standard error as the measure accompanying each mean: 1.8 for acupressure and 2.5 for ondansetron. In general, a standard error describes the sampling precision of an estimated quantity, such as a mean. It is not the same as the standard deviation, which describes the dispersion of individual observations around a group mean. A standard error can be useful for understanding uncertainty in a mean, but it does not by itself show the full distribution of individual scores.

The registry record does not post individual participant scores or a distribution plot in the registry record described for this analysis. It is therefore not possible to assess skewness, outliers, floor or ceiling patterns, or whether the numerical scale behaved similarly in the two groups. General statistical practice considers these features when selecting or checking a model for continuous outcomes. No such diagnostic information or method details are reported in the registry record.

How should the p-value be read?

The comparison reports an unadjusted p-value of 0.838. In general, a p-value measures how unusual data at least as incompatible with a null hypothesis would be, assuming that null hypothesis and the statistical model are correct. It is not the probability that the null hypothesis is true, and it is not a measure of the probability that an intervention is beneficial or harmful. A large p-value does not establish that the groups are equivalent. The record does not state the precise test used, any model diagnostics, or a prespecified threshold for interpreting the comparison.

The p-value should be considered together with the estimated contrast and its confidence interval. A point estimate alone can be misleading when the data are imprecise, and a p-value alone does not show the range of plausible effect sizes. The interval extends from -6.668 to 5.408, which makes the uncertainty visible on the score-change scale. The confidence level for this interval is not reported in the registry record, so no confidence percentage is attached to it in this explanation.

Why do design details matter?

Random allocation is intended, in general, to make treatment groups comparable on average with respect to factors present before assignment. It does not guarantee balance in a small set of participants, and it does not remove uncertainty due to limited data. The record identifies the study as randomized, but does not describe the sequence-generation or concealment procedures. It also lists no masking. Awareness of group assignment can potentially affect care, reporting, or outcome assessment; the record does not describe safeguards or evaluate whether these possibilities influenced the score.

The parallel-group design means the treatment groups are compared as separate arms rather than as a crossover in which each participant receives both treatments. The posted endpoint is a before-and-after change within each participant, but the between-group comparison remains the contrast between arm means. The record does not report how missing measurements were handled or whether the analysis followed original assignment regardless of treatment received. Those features are necessary for a fuller assessment of the analysis but are not reported in the registry record.

What can planning calculations tell readers?

The planning illustrations use the observed effect as a reference and consider planning for 100%, 75%, and 50% of that effect. They assume a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The figures are participants per arm for this continuous-outcome comparison. In general, smaller effects require more participants to detect under otherwise unchanged assumptions. These calculations are illustrative and do not establish what the trial originally planned or what effect investigators considered important. The original design assumptions and sample-size justification are not reported in the registry record.

In general, planning calculations depend on assumptions about the effect worth detecting, variability, allocation, significance threshold, and desired power. A planning result is conditional on those inputs; it is not a statement about what the completed study had a particular probability of detecting after its results were known. The registry record also does not report an interim-analysis plan, monitoring boundaries, or a prespecified statistical analysis plan. Without those details, the reported comparison can be described, but the full path from original protocol to posted analysis cannot be reconstructed.

Because the outcome is a continuous score rather than an event count, methods for count data and over-dispersion are not directly indicated by the posted endpoint description. In general, over-dispersion matters when count outcomes vary more than a model assumes, which can make uncertainty estimates unreliable if ignored. That general issue should not be imported into this score analysis without evidence that a count model was used. The registry record reports a mean-based endpoint and does not give enough analytic detail to identify a more specific model.

10. Confidence Intervals and Precision

The posted comparison has a mean difference of -0.63 and a confidence interval from -6.668 to 5.408. The interval is broad relative to the point estimate and spans zero. In practical terms, the point estimate alone gives only one possible summary of the group contrast, while the interval displays substantial uncertainty about its size and direction. The interval does not establish that the groups have the same mean change.

In general, a confidence interval is a range of estimates that reflects uncertainty arising from sampling, under the method's assumptions. A narrower interval indicates greater precision than a wider interval on the same scale. The confidence level attached to the posted interval is not reported in the registry record, so its nominal coverage level cannot be specified. The interval should also not be interpreted as covering all uncertainty: it does not account automatically for design limitations, measurement issues, or incomplete reporting.

The group summaries report standard errors of 1.8 for acupressure and 2.5 for ondansetron, with 12 participants in each group. These standard errors describe uncertainty in the group means, not the range of individual scores. No interval is posted for either arm mean in the record. The group-level information therefore does not show how participants' scores were distributed or whether unusual values influenced the means.

The unadjusted p-value is 0.838. It is consistent with the broad uncertainty conveyed by the interval, but it should not replace the interval as a description of precision. The planned enrollment of 300 and the posted outcome group sizes of 12 each also require context: the registry does not explain why those figures differ or which participants were included in the analysis. This limits assessment of how precisely the result represents the intended study population.

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 sample-size display is a planning illustration based on the observed effect, not a record of the trial's original enrollment calculation. For this continuous mean comparison, the entries are participants per arm, not total events. The stated planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect used for each illustration is a stated fraction of the observed effect.

The 80% power column gives the number of participants per arm the planning calculation estimates would be needed to have an 80% chance of detecting the specified effect under the stated assumptions, if the effect and model assumptions were correct. The 90% power column gives the corresponding number per arm for a higher target chance of detection. These are planning concepts, not guarantees about what a future study would find. The registry record does not report the original study's design assumptions or its sample-size justification.

The entries consider planning for 100% of the observed effect, 75% of the observed effect, and 50% of the observed effect. The corresponding displayed requirements rise as the assumed effect becomes smaller: for 80% power, the figures are 2,253, 4,004, and 9,009 participants per arm; for 90% power, they are 3,015, 5,360, and 12,060 participants per arm. In general, a smaller effect is harder to distinguish from random variation, so more participants are needed when other assumptions remain unchanged.

Because the calculations use the observed effect as a reference, they are sensitive to uncertainty in that estimate. They should not be read as evidence that the completed study had a particular chance of finding a difference. This is not observed power. The registry's planned enrollment of 300 is a separate study-record figure; the planning illustrations do not explain how that enrollment target was chosen.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -0.630; pooled standard deviation σ = 7.546.
2. n = 2 × (1.96 + 0.842)² × 7.546² / -0.630² = 2,252.0, rounded up to 2,253 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- -0.63                      # observed difference in means
sigma <- 7.54585979196539                     # 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(3075163)
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 = 2,253 (80% power), 3,015 (90% power)
 75% of observed effect: n per arm = 4,004 (80% power), 5,360 (90% power)
 50% of observed effect: n per arm = 9,009 (80% power), 12,060 (90% power)
power.t.test: 2253 
Simulated power at n = 2,253 per arm: 0.798 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Multiplicity, Missing Data and Analysis Populations

The record posts one primary outcome measure and no secondary outcome results. It reports zero posted analyses in the analysis count, despite presenting a primary outcome comparison. The registry does not describe how that count relates to the posted outcome result. No multiplicity strategy is reported, such as whether multiple comparisons were planned or whether any adjustment was used. With only one primary outcome identified in the posted record, the available information does not allow a fuller assessment of how outcomes or comparisons were selected.

Missing-data handling is not reported in the registry record. The posted outcome groups each contain 12 participants, while planned enrollment is 300. The record does not say how many participants were enrolled, randomized, treated, assessed, or excluded from the posted outcome analysis. It also does not state whether any outcome measurements were missing, why they might be missing, or how missing values were handled. The difference between planned enrollment and the posted outcome group sizes should not be attributed to a particular cause without that information.

The analysis population is not reported. The record does not identify whether the comparison includes all randomized participants, only those who received treatment, only those with complete measurements, or another group. It also does not explain whether participants were analyzed according to assigned group or treatment received. These distinctions can affect interpretation, especially when group sizes in the posted results are small.

Details of an interim-analysis plan, stopping rules, data monitoring, and the prespecified statistical analysis plan are not reported in the registry record. The registry status is terminated, but no reason for termination is given. Without information on outcome timing, missingness, analysis populations, and decision procedures, readers cannot determine whether the posted result reflects the originally intended analysis or assess possible effects of incomplete reporting. These gaps do not prove that a particular problem occurred; they define what cannot be established from the record.

14. 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 serious adverse event figures list 12 participants at risk in each arm. The reported number affected by serious adverse events is 0 for acupressure and 0 for ondansetron. The record also reports 0 affected by other adverse events in each group, and 0 deaths in each group. No serious adverse event terms are listed.

These are counts in the posted safety groups, not a complete characterization of every possible harm. In general, zero recorded events in a small group does not establish that an event cannot occur; it means no events were recorded in the listed group for the reported category. The record does not describe how adverse events were collected, the observation period for safety, or the criteria used to classify events. It also does not provide detailed event narratives or participant characteristics.

The at-risk counts are 12 in each arm, matching the posted primary-outcome group sizes, but the registry does not explain whether the safety and efficacy populations were defined identically. The figures should be read as registry-reported counts, not as proof of the absence of all adverse experiences or as a comparison demonstrating a safety difference between treatments.

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

The posted results describe a mean nausea-score change of 1.88 in the acupressure arm and 1.25 in the ondansetron arm, with 12 participants in each group. The registry comparison reports a mean difference of -0.63 for ondansetron, a confidence interval from -6.668 to 5.408, and an unadjusted p-value of 0.838. Together, these statistics indicate that the estimated contrast is uncertain; the interval includes zero and extends to values on either side.

These results do not show that the treatments are equivalent. Demonstrating equivalence or non-inferiority requires a prespecified margin and an analysis designed for that question, neither of which is reported in the registry record. A nonsignificant p-value is not proof of no difference. Nor does the point estimate alone establish that one approach is better. The record's description says a greater score difference is better, but it does not explain the subtraction order used to construct the change score, so the sign should not be given an unreported clinical interpretation.

The findings address one primary endpoint at one stated timeframe: nausea-score change by discharge from the post anesthetic care unit. They do not establish results for other outcomes such as symptom duration, later recurrence, rescue medication use, or overall recovery. No secondary outcome results are posted. The safety counts show no serious adverse events, other adverse events, or deaths recorded in either group in the posted figures, but the safety observation and collection details are not reported.

The registry lists planned enrollment of 300, while the posted outcome groups each contain 12 participants. The reason for this difference is not reported. The study is marked terminated, but the reason is also not reported. These registry entries limit what can be concluded about representativeness, completeness, and the conduct of the study. The result should therefore be treated as a small, imprecise posted comparison, not as a definitive estimate or a basis for medical advice.

16. Why This Trial Matters Statistically

This study illustrates why an estimated difference, its uncertainty, and the size of the analyzed groups should be read together. The two posted arm means differ numerically, but the reported confidence interval extends across zero and is broad. That combination makes precision central to interpretation: the point estimate is not enough to establish the size or direction of an underlying group difference.

It also distinguishes a planned enrollment figure from the number of participants contributing to posted results. The registry lists planned enrollment of 300, while the outcome summaries include 12 participants per arm. Since the record does not explain the gap, readers cannot determine whether it reflects recruitment, outcome availability, analysis choices, or another cause. Transparent reporting of participant flow and analysis populations is important for understanding what a trial estimate represents.

The study's status is terminated, but the reason is not reported. A status label alone cannot establish whether termination was related to recruitment, operations, safety, results, or another issue. Similarly, the posted safety counts are useful but do not resolve the absence of detail about event collection and follow-up. These are examples of how registry records can provide important data while leaving key questions unanswered.

Finally, the planning illustrations demonstrate the dependence of sample-size requirements on the effect targeted. Smaller assumed effects require more participants under the stated assumptions. Those calculations are distinct from the trial's original sample-size justification, which is not reported, and from evidence about the completed study's ability to answer its question. Together, the endpoint, contrast, interval, and reporting gaps offer a practical lesson in separating numerical results from the strength and scope of the conclusions they support.

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 posted outcome groups are small, with 12 participants in each arm, and the comparison's confidence interval is broad. The record does not explain why the planned enrollment of 300 differs from the posted group sizes. Without participant flow or analysis-population information, it is not possible to assess whether the reported groups represent all randomized participants or whether outcome availability affected inclusion.

The record identifies a randomized design but does not report sequence generation or allocation concealment. It lists no masking. Since the endpoint relies on a nausea score, unmasked reporting and assessment could be relevant in general, but the registry does not describe how scoring was administered or whether outcome assessment was standardized. The operational details of the score-change calculation are also not given beyond the before-and-after description and the statement that a greater difference is better.

The reason for termination is not reported. Nor are the study's original sample-size assumptions, its statistical analysis plan, missing-data methods, analysis populations, interim analyses, or multiplicity procedures. The record does not post secondary outcome analyses or detailed participant characteristics. These gaps prevent a complete appraisal of how the study was planned and how the posted comparison relates to its original objectives.

The endpoint is limited to nausea-score change by discharge from the post anesthetic care unit. The record does not describe later outcomes or provide information about rescue-medication use during the measurement period. Safety figures are counts without details about the observation period or collection procedures. These limitations do not show that a specific bias or problem occurred; they indicate where the registry information is insufficient for stronger conclusions.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Post-Operative Therapy for Nausea or Vomiting — NCT03075163.
• Registry record last updated 2019-06-18; status last verified 2019-06.
• Results first posted 2019-06-04.
• 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

NCT03075163 is a phase 4, single-site, prospective randomized study of acupressure versus ondansetron for postoperative nausea or vomiting. The design is parallel group, and masking is listed as none. The registry record lists planned enrollment of 300, a start date of 2016-10-18, primary completion in 2017-04, and status terminated.

The primary endpoint is mean change in nausea score by discharge from the post anesthetic care unit. The posted outcome groups include 12 participants each. The mean difference reported for ondansetron is -0.63, with a confidence interval from -6.668 to 5.408 and an unadjusted p-value of 0.838. No secondary outcome results are posted. The record reports 0 serious adverse events, 0 other adverse events, and 0 deaths in each group. The reason for termination, original sample-size justification, analysis population, and missing-data handling are not reported in the registry record.