Clinical Comparison of the Airway Devices: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Clinical Comparison of the Airway Devices (NCT00581386), a randomized na study. The primary outcome is Duration of Intubation.

2. Clinical Question

The registry describes a randomized clinical comparison of three airway devices in adult patients. The central statistical question is whether the mean time to successful placement differs between LTS-D and either comparator. The primary endpoint is a continuous measure: elapsed time in seconds until the device is successfully placed. The record reports group means and standard deviations, along with pairwise mean-difference estimates and confidence intervals.

The question is limited to the measured placement-time outcome. The study summary also mentions device insertion, position, drain-tube patency and anatomic sealing properties, but separate posted numerical results for those measures are not included in the registry results. The record lists six outcome measures and five analyses, but does not report secondary numerical results. It therefore does not support conclusions about those other device characteristics.

These comparisons concern the observed results in the enrolled trial groups. The registry record does not describe the criteria used to select participants in enough detail to determine how broadly the findings might apply beyond this study setting.

3. Trial Design

The registry identifies this as a randomized, single-masked, parallel-group study of three devices: LTS-D, ETC and PLMA. It lists enrollment as 218 and status as completed. The listed phase is NA, and the intervention type for each device is DEVICE. The sponsor is The University of Texas Health Science Center, Houston.

The record lists study start as 2007-05 and primary completion as 2009-04. Those registry dates give the recorded study timeline, but do not describe recruitment duration for individual participants or the timing of outcome assessment beyond the endpoint's stated measure. Details such as the randomization sequence, allocation concealment, which parties were masked, and the procedures used to maintain masking are not reported in the registry record. The label “single-masked” alone does not identify who was masked.

The primary result includes 73.0 participants in the LTS-D group, 73.0 in the ETC group and 72.0 in the PLMA group. Those are the group counts displayed for duration of intubation. The registry's arm descriptions state that patients were divided among the three groups, but do not give additional information about stratification, blocks or the process of assigning devices.

The listed primary endpoint is duration of intubation, defined as the time taken to successfully place the device in seconds. The endpoint is summarized as a mean with standard deviation. Although the registry lists six outcome measures and five analyses, numerical results are posted for the primary endpoint and the two comparisons described in the statistical results. A detailed protocol, the trial's original sample-size justification, and the full statistical analysis plan are not reported in the registry record.

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: There were no enrolled participants excluded from trial before assignment to groups.

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 Duration of Intubation, measured over duration of intubation.

The primary endpoint is duration of intubation: the time taken to successfully place the airway device, measured in seconds. It captures the elapsed time associated with successful placement rather than a clinical outcome after placement. The registry summarizes this continuous measure using a mean and standard deviation for each device group.

A mean provides a group-level description of the observed placement times. The standard deviation describes how spread out individual times are around that group mean. These summaries answer related but different questions: the mean describes the average time, while the standard deviation indicates variation among participants. A group can have a similar mean to another group while showing a different amount of variability.

Timing is relevant to the study's stated evaluation of device insertion. It gives a measurable way to compare the placement process across randomized groups. The registry's primary endpoint description does not specify additional operational details such as exactly when timing starts, what event stops the clock beyond successful placement, or how unsuccessful attempts are handled. Those details are not reported in the registry record.

The endpoint is not a complete assessment of device performance. The study summary also identifies position, drain-tube patency and anatomic sealing properties as study interests, but those characteristics are not represented by the duration measure alone. The posted primary outcome therefore answers a focused question about time to successful placement, not every question raised in the study summary.

7. Results Posted in the Registry

• Esophageal Tracheal Combitube(ETC): mean 30.80 versus 30.90 on control; difference -0.10 (95% CI -6.95 to 6.75), standardized effect d = -0.00; z-test p = 0.977.
• ProSeal Laryngeal Mask Airway (PLMA): mean 30.17 versus 30.90 on control; difference -0.73 (95% CI -9.18 to 7.72), standardized effect d = -0.03; z-test p = 0.866.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary endpoint is continuous, so the registry reports a mean and standard deviation for each device group. A mean summarizes the central value of the observed times. A standard deviation summarizes dispersion around that mean. Reporting both is useful because similar averages can arise from groups with different degrees of participant-to-participant variability. Here, the standard deviations are substantial in relation to the group means, which makes the uncertainty around comparisons important to consider.

What does a mean difference express?

A mean difference is a contrast between two group averages, expressed in the original outcome units. In this trial, the units are seconds. The posted comparisons use LTS-D as the reference group and compare it separately with ETC and PLMA. The ETC comparison estimate is -0.1 seconds; the PLMA comparison estimate is -0.73 seconds. An estimate close to zero indicates that the observed group averages are close, but it does not by itself show how precisely the difference has been estimated. The confidence interval gives additional information about that uncertainty.

How should the confidence intervals be read?

A confidence interval is an interval estimate intended to convey uncertainty around an estimated effect under the statistical method used. A narrower interval indicates more precision than a wider interval. The ETC interval extends from -6.953 to 6.753 seconds, and the PLMA interval extends from -9.182 to 7.722 seconds. Each interval contains zero, so the posted results are compatible with no mean difference as well as with differences in either direction. The registry record does not state the confidence level or provide enough method detail to reconstruct the interval procedure independently.

What does a p-value add?

The unadjusted p-values are 0.977 for ETC and 0.866 for PLMA. A p-value describes how unusual data at least as incompatible with a specified null hypothesis would be under that hypothesis and the test assumptions. It is not a measure of the probability that the null hypothesis is true, and it does not express the probability that a result will replicate. A large p-value does not establish equality or equivalence. The registry record labels these values unadjusted; whether any other analyses applied a correction is not reported in the registry record.

Why does variability matter?

When individual observations vary substantially, a group mean can be estimated less precisely than it would be with less variation and the same amount of information. This is why the standard deviations and confidence intervals matter alongside the means. In general, over-dispersion means that observed variation is greater than a model assumes. If a model fails to account for that extra variation, its uncertainty estimates can be too small. The posted primary outcome is analyzed as a continuous measure with group means and standard deviations; the registry record does not report a model or any assessment of over-dispersion.

What is and is not documented about the analysis?

The record identifies randomized allocation, single masking and a parallel model. It reports group summaries and pairwise mean-difference estimates. It does not report the original statistical analysis plan, the exact test used for the p-values, any covariate adjustment, handling of protocol deviations, or whether the primary analysis followed intention-to-treat principles. Missing-data methods and analysis-population definitions are also not reported in the registry record. These omissions limit how fully the calculations and assumptions can be assessed from the posted record.

The planning illustrations are separate from the observed trial analysis. They use the observed effect as a starting point and show planning values for detecting stated fractions of that effect under specified assumptions. These hypothetical planning calculations do not change the observed group summaries, confidence intervals or p-values. They also are not evidence that the trial was designed around those assumptions. The trial's own design assumptions and sample-size justification are not reported in the registry record.

10. Confidence Intervals and Precision

Precision concerns how tightly the data estimate a quantity, rather than whether an estimate is statistically significant. The two mean-difference estimates are -0.1 seconds for ETC versus LTS-D and -0.73 seconds for PLMA versus LTS-D. Their confidence intervals are -6.953 to 6.753 seconds and -9.182 to 7.722 seconds, respectively. Both intervals include zero and extend to values on either side of it.

The intervals are wide in relation to the estimated differences. This means the posted summaries do not pin down the mean difference narrowly. For ETC, the interval is compatible with a negative or positive difference across its stated limits; the same is true for PLMA. The observed estimates are near zero, but the data do not confine the plausible values to a narrow range around those estimates. The results therefore should not be read as demonstrating that the devices have identical average placement times.

Standard deviations also show variation in observed duration within each group: 18.7 seconds for LTS-D, 23.3 seconds for ETC and 31.53 seconds for PLMA. These figures describe participant-level spread, not uncertainty in the mean difference itself. The confidence intervals are the direct summaries of uncertainty for the pairwise estimates.

The registry record does not state the confidence level associated with the intervals, nor does it report a prespecified margin that would define a difference as negligible. Without such a margin, the intervals cannot establish equivalence. They describe the range of values compatible with the reported analysis, subject to the method's assumptions, rather than guaranteeing that the true difference lies within the displayed limits.

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 values are participants per arm for the pairwise comparisons, not total event counts. They are planning illustrations based on the observed effect, not the trial's original design justification. The calculation assumptions listed in the registry record are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is the stated fraction of the observed effect. The trial's own original sample-size assumptions are not reported in the registry record.

For ETC compared with LTS-D, planning for 100% of the observed effect gives 700,576 participants per arm for 80% power and 937,872 participants per arm for 90% power. Planning for 75% of the observed effect gives 1,245,468 participants per arm for 80% power and 1,667,328 participants per arm for 90% power. Planning for 50% of the observed effect gives 2,802,302 participants per arm for 80% power and 3,751,487 participants per arm for 90% power.

For PLMA compared with LTS-D, planning for 100% of the observed effect gives 19,727 participants per arm for 80% power and 26,409 participants per arm for 90% power. Planning for 75% of the observed effect gives 35,070 participants per arm for 80% power and 46,948 participants per arm for 90% power. Planning for 50% of the observed effect gives 78,906 participants per arm for 80% power and 105,633 participants per arm for 90% power.

In plain language, the 80% power column gives the calculated participants per arm for a design with an 80% chance of detecting the specified effect under the listed assumptions if that effect were present. The 90% power column makes the analogous calculation for a 90% chance. Smaller effects require more participants to detect under the same assumptions. These figures are not observed power; they are hypothetical planning illustrations derived from the observed effects, which are very close to zero.

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 = -0.100; pooled standard deviation σ = 21.126.
2. n = 2 × (1.96 + 0.842)² × 21.126² / -0.100² = 700,575.3, rounded up to 700,576 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 <- -0.0999999999999979                      # observed difference in means
sigma <- 21.1255769151993                     # 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(581386)
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 = 700,576 (80% power), 937,872 (90% power)
 75% of observed effect: n per arm = 1,245,468 (80% power), 1,667,328 (90% power)
 50% of observed effect: n per arm = 2,802,302 (80% power), 3,751,487 (90% power)
power.t.test: 700576.3 
Simulated power at n = 700,576 per arm: 0.797 (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 six outcome measures and five analyses, but the primary result discussed in the record is duration of intubation, with pairwise comparisons of LTS-D against ETC and PLMA. The two reported p-values are explicitly unadjusted. Whether the trial used a multiplicity adjustment across comparisons or outcomes is not reported in the registry record. When several comparisons are considered, multiplicity is a general statistical concern because the chance of at least one apparently notable result can increase as more tests are performed. No correction should be assumed in the absence of a reported method.

The registry record does not report an interim-analysis plan, stopping boundaries, or whether any interim looks at outcome data occurred. It also does not report the prespecified hierarchy, if any, among primary and secondary outcomes. Consequently, the posted p-values should be understood as the unadjusted comparison values recorded, not as evidence that the broader analysis family was controlled for multiple testing.

Missing-data handling is not reported in the registry record. The primary outcome has group counts of 73.0 for LTS-D, 73.0 for ETC and 72.0 for PLMA, but the record does not explain whether these counts represent every randomized participant, participants with observed outcomes, or another analysis set. It does not describe exclusions, withdrawals, failed placements, or how such cases were incorporated into the endpoint analysis.

The analysis population is likewise not defined. The record does not say whether analyses were intention-to-treat, per-protocol, or based on another population definition. Randomized allocation is reported, but that alone does not establish how participants were handled after randomization. These gaps limit assessment of possible bias from missing outcomes, exclusions or deviations from assigned treatment.

Further information about the statistical analysis plan, prespecified outcome hierarchy, multiplicity handling, interim analyses, missingness and analysis populations is not reported in the registry record.

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 registry reports zero serious adverse events among the 73 participants at risk in the LTS-D group, zero among the 73 at risk in the ETC group, and zero among the 72 at risk in the PLMA group. The record also reports zero other adverse events in each of those groups, using the same group counts at risk.

These are the adverse-event counts posted for the groups. A count of zero means that no event in that category was recorded in the registry results for the stated group; it does not prove that the underlying risk is absent. The registry record does not provide event descriptions because no serious-event terms are listed. Death counts are not reported in the registry record.

The available information does not describe how adverse events were defined, collected, assessed for relationship to device, or monitored over time. It also does not report a follow-up duration for safety. The figures should therefore be read as the registry's posted counts, not as a complete characterization of safety or as a basis for comparing rare risks.

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

The posted primary outcome results describe similar mean placement durations across the three device groups: 30.9 seconds for LTS-D, 30.8 seconds for ETC and 30.17 seconds for PLMA. The pairwise mean-difference estimates are -0.1 seconds for ETC compared with LTS-D and -0.73 seconds for PLMA compared with LTS-D. Both confidence intervals include zero, and the unadjusted p-values are 0.977 and 0.866. Together, these figures do not provide strong statistical evidence of a mean difference in this endpoint under the reported comparisons.

That interpretation is not the same as demonstrating equivalence. The confidence intervals allow differences in either direction, and the registry record does not report a threshold for a clinically unimportant difference. A failure to find strong evidence against no difference cannot prove that the true mean durations are identical. The uncertainty is especially important because the confidence intervals cover a range wider than the near-zero point estimates.

The endpoint captures time to successful placement, not the full set of device features named in the study summary. The record describes interest in position, drain-tube patency and sealing properties, but numerical results for those characteristics are not reported among the posted results. The primary outcome cannot answer those separate questions. Nor do these results, by themselves, establish anything about outcomes after device placement.

The results are also bounded by the record's reporting detail. Eligibility criteria, the precise analysis population, missing-data handling, trial-specific sample-size justification and full analysis methods are not reported in the registry record. Those omissions make it harder to judge generalizability and the sensitivity of the conclusions to analysis choices.

Accordingly, the statistical reading is focused: the registry reports close observed group means for duration of intubation, with uncertain pairwise estimates that include no difference. The posted results neither establish exact equality nor settle broader comparisons of device performance.

16. Why This Trial Matters Statistically

This trial illustrates why a point estimate, its uncertainty and the study question need to be read together. The group means are close, but that observation alone does not establish that the devices have the same average placement time. The confidence intervals extend across zero and cover values on both sides of the estimated differences, making precision central to interpretation.

It also shows the distinction between statistical evidence and practical importance. A p-value does not state whether a difference would matter in a clinical setting, and the registry record does not define a meaningful threshold for duration. Without a prespecified margin, the result cannot be framed as an equivalence finding. The estimates and intervals describe the evidence for this specific continuous endpoint.

The planning illustrations demonstrate how strongly a sample-size calculation can depend on the effect chosen for detection. Because the observed estimates are close to zero, the resulting planning figures are very large, and smaller target effects lead to still larger figures under the stated assumptions. These calculations are hypothetical; they do not reveal the original reasoning behind trial enrollment. The trial's own sample-size justification is not reported in the registry record.

Finally, the record highlights the value of complete reporting. Details about masking, analysis populations, missing outcomes, multiplicity and interval construction would help readers evaluate the results more fully. The statistical lesson is not that the posted comparisons settle every device question, but that conclusions should match the endpoint, precision and reporting detail actually available.

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 registry provides limited methodological detail beyond identifying randomized allocation, single masking and a parallel model. It does not specify who was masked, how allocation was concealed, or how randomization was implemented. These details are not reported in the registry record, so the risk of bias related to assignment and masking cannot be fully assessed.

The record does not define the analysis population or explain whether all randomized participants contributed to the primary endpoint. Although group counts are listed, their relationship to the full randomized population is not described. Handling of missing observations, unsuccessful placement, exclusions and protocol deviations is not reported in the registry record.

Only the primary endpoint comparisons have numerical results in the described posted results. The study summary names device position, drain-tube patency and sealing properties, but numerical results for those measures are not reported in the registry record. The record also does not provide participant characteristics or detailed eligibility criteria, limiting assessment of how the enrolled population relates to other settings.

The primary outcome is summarized by means and standard deviations, but the exact analysis method, confidence level and assumptions behind the reported intervals are not specified. The p-values are unadjusted, and multiplicity handling is not reported. No clinically important difference or equivalence margin is given. These limitations counsel against treating the comparisons as proof of equality or as a comprehensive assessment of the devices.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Clinical Comparison of the Airway Devices — NCT00581386.
• Registry record last updated 2016-09-20; status last verified 2016-08.
• Results first posted 2010-03-04.
• 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

The registry record describes a completed randomized, single-masked, parallel-group comparison of LTS-D, ETC and PLMA in adult patients. Enrollment is listed as 218. The primary endpoint is duration of intubation in seconds, summarized as a mean and standard deviation.

Mean durations were 30.9 seconds for LTS-D, 30.8 seconds for ETC and 30.17 seconds for PLMA. The posted pairwise mean-difference estimates versus LTS-D were -0.1 seconds for ETC and -0.73 seconds for PLMA. Both confidence intervals include zero; the unadjusted p-values were 0.977 and 0.866.

The registry reports zero serious and zero other adverse events in each group. It does not report death counts, detailed analysis methods, missing-data handling, or numerical results for the other device characteristics named in the study summary. The results support a focused interpretation of the posted placement-time comparisons, with uncertainty and reporting limitations kept in view.