Ear Acupuncture for Pain Associated With Ambulatory Arthroscopic Knee Surgery: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Ear Acupuncture for Pain Associated With Ambulatory Arthroscopic Knee Surgery (NCT01447329), a randomized na study. The primary outcome is Number of Participants With a Decrease in Pain Level.

2. Clinical Question

This is a question about a recorded pain outcome in the setting of ambulatory knee surgery, not a general comparison of acupuncture for pain in other settings. The registry also describes follow-up contacts by phone, email, or text message after discharge, including questions about pain, ambulation, analgesic doses, and time to return to full duty. It states that the PIQ-6 Pain Impact Questionnaire was to be asked at 1 week and 1 month. Those details describe planned assessments; the registry record does not provide posted results for those other measures.

3. Trial Design

The registry identifies NCT01447329 as a completed, randomized, parallel-group trial with triple masking. It records an enrollment of 49. The listed sponsor is Mike O'Callaghan Military Hospital. The trial is listed as phase NA, and its condition is Pain. The registry gives a start date of 2011-12 and a primary completion date of 2014-01.

The trial compares standard treatment plus ear acupuncture with a standard arm. The brief summary describes standard of care alone as the comparator, but the arm description for the standard arm says “placebo.” The record does not explain how these labels relate to the actual comparator procedures. The acupuncture description specifies points on both ears, but further details such as treatment frequency and duration are not reported in the registry record.

The stated follow-up plan includes contacts after discharge at 24 and 48 hours, 1 week, and 1 month, as well as assessments during Post Anesthesia Care Unit and Same Day Surgical Unit admissions. The planned contacts included pain, ambulation status, analgesic doses, and time to return to full duty. The PIQ-6 Pain Impact Questionnaire was named for assessment at 1 week and 1 month. These descriptions do not establish which assessments were completed for each participant or how missing assessments were handled.

The registry lists three outcome measures, but only the primary outcome is detailed in the posted results represented by these registry entries; no secondary outcome results are posted. The primary outcome is the count of participants with a decrease in pain level. The record does not describe the trial’s original sample-size calculation, its detailed statistical analysis plan, or the analysis population. The posted enrollment and outcome counts describe what is recorded, not the rationale for the trial’s design.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

5. Baseline Characteristics

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

6. Primary Endpoint

The registry lists the primary outcome as Number of Participants With a Decrease in Pain Level, measured over during PACU (Post Anesthesia Care Unit) and SDSU (Same Day Surgical Unit) admissions, 24 and 48 hours, 1 week and 1 month.

The primary endpoint is titled “Number of Participants With a Decrease in Pain Level.” It is a count of participants classified as having a decrease, rather than a measure of the average amount of pain change. The registry associates it with assessments during Post Anesthesia Care Unit and Same Day Surgical Unit admissions, at 24 and 48 hours, 1 week, and 1 month.

A count of participants with an event can make an outcome easier to interpret than a complex measurement scale: it describes how many participants met the recorded event criterion in each arm. But the usefulness of that count depends on how the event is defined. The registry record does not state the threshold for a decrease, the reference point used to judge a decrease, or whether a participant had to meet the criterion at any one assessment or at a particular assessment.

The posted counts are 18 in the standard-treatment-plus-acupuncture arm and 16 in the standard arm. Their denominators are 24 and 25, respectively. These counts alone do not show the timing or magnitude of any pain change. Nor do they describe pain scores, analgesic use, or functional outcomes. Those outcomes are mentioned in the study summary, but their results are not reported in the registry record.

This endpoint is used to compare the recorded occurrence of a pain decrease between randomized arms. It should be read as a binary event outcome, with the stated limitations in event definition and assessment timing in mind.

7. Results Posted in the Registry

• Standard: 64.0% (16/25) versus 75.0% (18/24) on control; risk difference -11.0 percentage points (95% CI -36.6 to 14.6), risk ratio 0.85 (0.59–1.24); unadjusted two-proportion z-test p = 0.404.

8. Statistical Interpretation

9. Statistical Methods Explained

What does the risk difference describe?

The outcome is binary: a participant is counted as having a decrease in pain level or is not counted as having one. A risk difference compares the proportions with the event in the two arms. Unlike a relative measure, it describes an absolute difference between those proportions. The posted proportions are 0.75 for standard treatment plus ear acupuncture and 0.64 for standard. The reported risk difference is -0.11 because its comparison is encoded as the standard arm minus the acupuncture arm. The negative sign therefore corresponds to a larger observed event proportion in the acupuncture arm.

The sign is not a judgment about whether the result is clinically important. Interpretation depends on the endpoint definition, the scale and direction of the comparison, and the uncertainty around the estimate. Here, the registry does not define the required decrease in pain, and the risk difference is unadjusted. It is a comparison of the posted group summaries, not an estimate adjusted for participant characteristics or other factors.

What does the confidence interval add?

A confidence interval expresses uncertainty around an estimated effect. In general, it indicates a range of effect values compatible with the data and the method used to construct the interval. It is not a guarantee that the true effect lies within the interval, nor does it describe the range of individual participants’ outcomes. In this trial, the interval for the risk difference extends from -0.366 to 0.146, crossing zero. That means the posted data do not distinguish clearly between a negative difference, no difference, and a positive difference under the interval’s calculation.

Confidence intervals are particularly useful alongside a point estimate because a single estimate can conceal substantial uncertainty. The interval is wide relative to the scale of the risk difference, so the data do not pin down the direction and size of the underlying difference closely. A confidence interval does not correct for missing data, an unclear endpoint definition, or other limitations in the registry record.

How should the p-value be understood?

The posted unadjusted p-value is 0.404. In general, a p-value measures how unusual data at least as discrepant as those observed would be under a specified null hypothesis and statistical model. It is not the probability that the null hypothesis is true, and it is not a measure of the probability that the intervention has a particular effect. A larger p-value does not establish that the groups are equivalent. Equivalence requires a prespecified margin and an appropriate analysis, neither of which is reported in the registry record.

The p-value and confidence interval address related aspects of the comparison, but neither replaces judgment about the effect estimate, endpoint, and uncertainty. The p-value is unadjusted, and the registry record does not report a statistical analysis plan that would clarify whether it was the intended primary test or how other analyses were to be handled.

Why can over-dispersion matter?

For a binary outcome, the data are counts of participants with and without the event. General statistical models often rely on assumptions about how those outcomes vary around an underlying event probability. Over-dispersion means that observed variation is greater than the model expects. If present and not accounted for, uncertainty estimates can be too narrow and tests can appear more decisive than warranted. This is a general consideration for count and binary-outcome analyses; the registry record does not report an over-dispersion assessment for this trial.

Randomization supports comparison by assigning participants to study arms, but does not remove the need to inspect outcome definitions, missingness, and analysis choices. The trial is listed as randomized and triple masked, but details of the randomization procedure, the allocation concealment process, the masking roles, and the analytic handling of the outcome are not reported in the registry record.

What is the scope of the posted calculation?

The risk difference and its interval are unadjusted calculations from the posted summary statistics. They summarize the recorded event counts without accounting for covariates, repeated measurements, or variation across assessment times. The registry record gives a single primary count outcome associated with several assessment periods, but does not explain whether the counts combine those periods or how repeated observations were reduced to a participant-level outcome. That uncertainty prevents a more detailed reconstruction of the endpoint analysis.

The record lists zero posted analyses and does not include a sponsor analysis that can be compared with the unadjusted summary calculation. It also does not report whether there were interim analyses, what multiplicity strategy was intended, or how the analysis population was defined. Those omissions should not be filled in by assuming common practices. The posted comparison can describe the summary counts, but it cannot establish the full analysis process behind the completed trial.

10. Confidence Intervals and Precision

The point estimate for the risk difference is -0.11. Its confidence interval extends from -0.366 to 0.146. Because the interval crosses zero, the data are compatible with a difference in either direction as well as with no difference. The range is broad enough that the point estimate alone gives an incomplete impression of the uncertainty.

Precision concerns how narrowly the data locate an estimated effect, not whether the estimate is important or whether the study was conducted correctly. The posted interval does not identify a single likely effect with confidence; it covers negative and positive values. It therefore leaves uncertainty about both the direction and size of the difference in the event proportions.

The group counts are modest, and the endpoint is a participant count. With limited information, estimates of proportions and their differences can remain uncertain. The registry does not report the trial’s original sample-size assumptions, and its endpoint definition is not detailed enough to determine how each assessment time contributed to the count. The confidence interval quantifies sampling uncertainty under its calculation, but does not capture every uncertainty arising from outcome definition, missing data, or analysis choices.

The interval should be interpreted together with the event counts, the unadjusted p-value of 0.404, and the record’s reporting gaps. It does not prove that the groups have equal outcomes, nor does it establish a meaningful difference. It indicates that the posted data do not estimate the risk difference precisely.

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. The outcome is a participant count rather than a time-to-event outcome, so the registry’s planning convention for this result is a per-arm participant count. The figures are illustrations based on the observed effect, not the trial’s original design calculation.

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 to detect is set as a stated fraction of the observed effect. The 80% power column describes the number of participants per arm used in the illustration to give an 80% chance of detecting that assumed effect under those assumptions if it is present. The 90% power column gives the corresponding illustration for a 90% chance. These are planning quantities, not observed outcomes or evidence about the probability that the trial’s conclusion is correct.

For 100% of the observed effect, the illustration gives 274 participants per arm for 80% power and 367 participants per arm for 90% power. For 75% of the observed effect, it gives 475 participants per arm for 80% power and 636 participants per arm for 90% power. For 50% of the observed effect, it gives 1,040 participants per arm for 80% power and 1,391 participants per arm for 90% power. Smaller effects need more participants to detect under the same planning assumptions, which is why the figures rise as the target fraction of the observed effect becomes smaller.

These calculations are not observed power. They are illustrative planning estimates based on the observed effect and the stated assumptions. The registry record does not report the assumptions used for the trial’s original design or its original planned sample size.

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, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.750; treatment proportion p₁ = 0.640; average p̄ = 0.695.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.6511 = 1.2762.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.6465 = 0.5441.
4. n = (1.2762 + 0.5441)² / (-0.1100)² = 273.8, rounded up to 274 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
p0 <- 0.75                          # control proportion
p1 <- 0.64                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^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 (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(1447329)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 274 (80% power), 367 (90% power)
 75% of observed effect: n per arm = 475 (80% power), 636 (90% power)
 50% of observed effect: n per arm = 1,040 (80% power), 1,391 (90% power)
power.prop.test: 273.8 
Simulated power at n = 274 per arm: 0.804 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-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 three outcome measures, but no secondary outcome results are posted in the record represented by these registry entries. The primary outcome is associated with multiple assessment periods: during Post Anesthesia Care Unit and Same Day Surgical Unit admissions, at 24 and 48 hours, 1 week, and 1 month. The record does not explain whether each period was tested separately, how repeated assessments were combined, or which time point was intended to carry the primary inference.

Multiplicity arises when several outcomes, time points, or comparisons are examined. In general, making more statistical tests can increase the chance of finding an apparently notable result by chance. A prespecified analysis plan may address that issue, but the trial’s multiplicity strategy is not reported in the registry record. It is not appropriate to infer that a correction was or was not used based on the posted summary alone.

The registry record does not report the number of participants with missing primary outcome data, the reasons for missingness, or the method used to handle missing observations. It also does not state whether the analysis followed intention-to-treat, per-protocol, or another population definition. These details matter because exclusions or missing follow-up can affect group comparability and the interpretation of an outcome count.

The trial summary describes post-discharge contacts and several assessments, but a description of planned follow-up does not show that every measurement was obtained. The posted counts and denominators are available, yet the record does not explain whether those denominators include every randomized participant or reflect an analysis subset. The statistical analysis plan, interim analyses, and any methods for handling repeated measures are not reported in the registry 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 registry records zero serious adverse events in the standard-treatment-plus-ear-acupuncture arm and zero in the standard arm. It also records zero other adverse events in each arm and zero deaths in each arm. The listed numbers at risk are 24 in the acupuncture arm and 25 in the standard arm.

These are the posted safety figures, not proof that no harms occurred. They describe events recorded in the registry fields and do not establish how events were defined, collected, or monitored. The record does not provide serious adverse event terms, which is consistent with no serious terms being listed, but it does not give narrative detail on safety assessment or follow-up completeness.

Zero recorded events can be difficult to interpret when the number of participants is limited or reporting details are sparse. The figures do not establish that uncommon events could be ruled out, and they should not be extended to settings or populations beyond this trial. They also do not provide a basis for medical advice. They are a description of the registry’s recorded safety outcomes only.

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

The primary result describes the recorded count of participants with a decrease in pain level: 18 in the standard-treatment-plus-ear-acupuncture arm and 16 in the standard arm. The corresponding posted proportions are 0.75 and 0.64. The unadjusted risk difference is -0.11, with a confidence interval from -0.366 to 0.146 and an unadjusted p-value of 0.404. The interval includes no difference and values in either direction, so the observed estimate is uncertain.

This result does not establish that the treatments are equivalent. It also does not establish a reliable difference between them. The confidence interval and p-value should not be read as evidence that the intervention does or does not work. They describe the uncertainty and statistical comparison for the posted endpoint, under the calculation used.

The endpoint is not defined in enough detail to determine the size of pain decrease required for an event or how observations at different assessment periods contributed to the count. The single posted comparison does not show the timing or magnitude of pain changes. Although the study summary names other measures, including analgesic doses, ambulation, return to full duty, and PIQ-6 responses, their results are not reported in the registry record. The primary count cannot stand in for those outcomes.

The scope is also limited to the trial’s setting: ambulatory arthroscopic knee surgery and the recorded comparison between standard treatment plus ear acupuncture and the standard arm. The comparator description is not fully consistent, since the summary says standard of care alone and the arm description says placebo. The trial’s randomized and triple-masked design is recorded, but procedural and analysis details are not available. The result should therefore be understood as an uncertain registry comparison with specific reporting limits, not as a complete account of every clinical outcome or safety question.

16. Why This Trial Matters Statistically

This trial is statistically instructive because its reported event counts appear straightforward, while important interpretation depends on details that the registry does not fully document. A participant count with a decrease in pain is simple to state, but a reader needs to know what qualifies as a decrease and how assessments across the stated periods were combined. Those definitions determine what the event count actually represents.

The comparison also illustrates why a point estimate and its uncertainty should be read together. The observed proportions are 0.75 and 0.64, and the risk difference is -0.11 when expressed as standard minus acupuncture. Yet the confidence interval ranges from -0.366 to 0.146. The point estimate alone might suggest a direction, but the interval shows that the data leave substantial uncertainty about direction and size.

Randomization and triple masking are important design features recorded for this trial, but their labels do not replace reporting of how allocation and masking were implemented or how outcomes were analyzed. Likewise, a completed status does not supply missing information about analysis populations, missing outcomes, or multiplicity. Statistical interpretation depends on both the numerical results and the clarity of the methods that connect those results to the research question.

The planning illustrations further emphasize that a sample-size calculation depends on the effect targeted and the assumptions used. Smaller target effects call for larger per-arm participant counts under the stated planning approach. Those illustrations are not the trial’s original design calculation and are not an assessment of observed power.

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.

Several trial-specific gaps constrain interpretation. The registry does not define the threshold for a “decrease in pain level,” identify a reference measurement, or clarify how the assessment periods were combined into the participant count. It is also unclear whether the endpoint reflects a decrease at any assessment or at a selected time. The aggregate counts cannot resolve these questions.

The comparator wording is inconsistent across the record: the study summary describes standard of care alone, while the arm description for “Standard” says “placebo.” The registry does not explain the placebo procedure or reconcile the descriptions. Details of acupuncture delivery beyond the named ear points are not reported in the registry record.

Although the trial is listed as randomized and triple masked, the randomization method, allocation concealment, identities of masked parties, and assessment of masking are not reported. The record also does not report the analysis population, missing-data handling, multiplicity approach, interim analyses, or full statistical plan. These are relevant to judging the reliability and scope of the posted comparison.

The registry lists three outcome measures, but secondary results are not posted. Outcomes described in the study summary, including ambulation, analgesic use, return to full duty, and PIQ-6 responses, therefore cannot be assessed from these results. The safety fields record zero events, but details of event definitions, collection, and follow-up are not reported. Finally, the registry’s original sample-size assumptions are not reported, so the planning illustrations based on the observed effect should not be mistaken for the trial’s prospective design rationale.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Ear Acupuncture for Pain Associated With Ambulatory Arthroscopic Knee Surgery — NCT01447329.
• Registry record last updated 2024-01-19; status last verified 2024-01.
• Results first posted 2024-01-19.
• 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

NCT01447329 is a completed randomized, triple-masked, parallel-group trial listed as phase NA, sponsored by Mike O'Callaghan Military Hospital. The registry records enrollment of 49, a start date of 2011-12, and a primary completion date of 2014-01. The trial concerns pain after ambulatory arthroscopic knee surgery.

The comparison is standard treatment plus ear acupuncture versus a standard arm. The primary endpoint is the number of participants with a decrease in pain level during admissions and at the stated follow-up times. The posted counts are 18 of 24 in the acupuncture arm and 16 of 25 in the standard arm. The unadjusted risk difference is -0.11, with a confidence interval from -0.366 to 0.146 and p-value 0.404.

The registry does not report secondary outcome results or analyses, and several details of the endpoint, analysis methods, missing data, and comparator are not reported in the registry record. The posted comparison should be read with those limitations and its uncertainty in view.