Comparison Study in Adult Surgical Patients of 5 Airway Devices: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Comparison Study in Adult Surgical Patients of 5 Airway Devices (NCT00602979), a randomized na study. The primary outcome is Percentage Distribution of Cook's Modification of Cormack-Lehane's Grading System. Each Study Subject Will Receive a Grade of 1, 2A, 2B, 3A, 3B, or 4 in the Cormack-Lehane Grading System..

2. Clinical Question

3. Trial Design

This was a prospective, randomized, parallel-group comparison of five airway devices in adult surgical patients undergoing elective procedures. The four indirect-laryngoscopy devices were compared with the Macintosh laryngoscope, which the registry identifies as the current standard and control. The registry reports single masking; it does not describe which participants or study personnel were masked or how masking was maintained.

The registry lists enrollment of 240. For the primary outcome, the posted summaries give 45 participants in each of the five device groups. The adverse-event summaries list 48 participants at risk in each group. These are distinct posted figures, and the registry record does not explain the different denominators or their relationship to enrollment.

The study start is recorded as 2008-04, and primary completion as 2009-09. The status is completed. The record lists one primary outcome measure and no posted secondary outcome measures. It describes the primary measure as a percentage distribution of Cook’s modification of the Cormack-Lehane grading system, while the posted arm summaries report a mean and standard deviation for each group. The original statistical analysis plan, including the planned handling of the categorical grades, is not reported in the registry record.

The study’s own sample-size justification, intended analysis populations, missing-data procedures, and any planned interim analyses are not reported in the registry record. The sample-size illustrations accompanying the posted comparisons are separate planning calculations based on observed effects; they are not descriptions of the trial’s original 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

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 Percentage Distribution of Cook's Modification of Cormack-Lehane's Grading System. Each Study Subject Will Receive a Grade of 1, 2A, 2B, 3A, 3B, or 4 in the Cormack-Lehane Grading System., measured over 1 time during laryngoscopy.

The primary endpoint classifies the best laryngeal view obtained during laryngoscopy, with or without anterior laryngeal pressure. Each participant receives one of six Cook-modified grades: 1, 2A, 2B, 3A, 3B, or 4. The registry groups grades 1 and 2A as easy views, grades 2B and 3A as restricted views, and grades 3B and 4 as difficult views. Its Cook modification maps these categories to an ordered numeric coding from 1 through 6.

This measure is used to describe visibility of the laryngeal inlet and related structures during the procedure. It captures an important aspect of the conditions encountered by the person performing laryngoscopy. The posted results summarize the coded grades using a mean and standard deviation, making it possible to compare group averages. However, the categories are ordered rather than naturally continuous: the difference between adjacent codes need not represent an equal change in laryngeal view. A group mean also cannot reveal how many participants fell into each grade or into the easy, restricted, and difficult groupings.

The endpoint is a view classification, not a direct measure of successful intubation, number of attempts, procedure duration, or complications. Those outcomes are not reported as posted secondary measures in the registry record. Thus the primary endpoint addresses laryngoscopic view, and its interpretation should remain specific to that measure.

7. Results Posted in the Registry

• Airtraq Optical Laryngoscope: mean 1.18 versus 1.98 on control; difference -0.80 (95% CI -1.39 to -0.21), standardized effect d = -0.56; z-test p = 0.008.
• Storz DCI Video Laryngoscope: mean 1.27 versus 1.98 on control; difference -0.71 (95% CI -1.30 to -0.12), standardized effect d = -0.49; z-test p = 0.019.
• GlideScope Video Laryngoscope: mean 1.47 versus 1.98 on control; difference -0.51 (95% CI -1.11 to 0.09), standardized effect d = -0.35; z-test p = 0.095.
• McGRATH Video Laryngoscope: mean 1.13 versus 1.98 on control; difference -0.85 (95% CI -1.43 to -0.27), standardized effect d = -0.60; z-test p = 0.004.

8. Statistical Interpretation

9. Statistical Methods Explained

The posted comparisons use the arm-level means, standard deviations, and participant counts to estimate unadjusted mean differences between each indirect-device group and the Macintosh control. The estimates and confidence intervals are recalculations from posted summary statistics. They should be understood as simple pairwise comparisons, not as evidence that the registry reported a particular fitted model or a multiplicity-adjusted analysis.

What does a mean difference represent?

For each comparison, the mean difference expresses the indirect-device group’s average coded grade relative to the Macintosh group. A negative estimate indicates a lower average coded grade in the indirect-device group. Because the grade coding orders views from more visible to less visible, that direction corresponds to a lower numerical grade. The estimate does not state how any particular participant’s view changed, nor does it show how the grades are distributed within either group.

As a general statistical point, a mean difference is easiest to interpret when a measure has equal, meaningful steps. These grades are ordered categories. Their numeric codes preserve order, but the record does not establish that each step is an equal interval. Averaging the codes can be a concise summary, but it may conceal differences in category patterns. For example, identical means can arise from different distributions across grades. Grade-specific counts or proportions would be needed to assess those patterns directly.

What do the standard deviations describe?

The standard deviation describes how spread out individual coded grades are around the group mean. It is not the uncertainty in the mean itself and does not describe the precision of the comparison by itself. The Macintosh standard deviation is 1.96; the indirect-device standard deviations are smaller in the posted summaries. The notable differences in spread are relevant because the groups may differ not only in average coded grade but also in how variable their grades are. A mean comparison does not fully characterize that variability.

As a general statistical point, a standard error describes uncertainty in an estimated mean or difference, whereas a standard deviation describes variation among observations. Confidence intervals use uncertainty in the estimate to give a range of values compatible with the data and calculation method. These intervals remain dependent on the assumptions of the method, including how the coded outcome is treated.

How should the p-values be read?

The unadjusted p-value measures how incompatible the observed comparison is with a null hypothesis of no difference, under the assumptions of the calculation. It is not the probability that the null hypothesis is true, and it does not measure the size or clinical importance of a difference. The reported unadjusted values are 0.008 for Airtraq, 0.019 for Storz DCI, 0.095 for GlideScope, and 0.004 for McGRATH. These values should be considered alongside estimates and confidence intervals, rather than treated as stand-alone conclusions.

As a general statistical point, testing several comparisons increases the opportunity for at least one small p-value to occur by chance when all null hypotheses hold. Adjustment methods can address that family of tests, but which method was planned or used is not reported in the registry record. The posted p-values therefore remain unadjusted, and no claim about multiplicity-controlled significance can be made.

Why does the ordinal outcome matter?

The endpoint’s categories have a clear order, from grades representing an easy view toward grades representing a difficult view. But a numeric code does not, by itself, make those categories continuous. A mean-based comparison assumes that the coded values can be summarized meaningfully as averages. As a general statistical consideration, ordinal outcomes can also be analyzed with methods that model ordered categories or with comparisons based on category distributions. The registry record does not report whether such analyses were planned or performed, and the posted outcome summaries do not provide enough information to reconstruct them.

The study is described as randomized, which is a design intended to support comparison between assigned groups. The registry does not report the randomization procedure, allocation concealment, analysis population, adherence to assigned devices, or missing-data methods. The single-masking designation is recorded, but masking details are absent. These omissions limit assessment of how the planned design was implemented and how the posted summaries relate to all randomized participants.

10. Confidence Intervals and Precision

A confidence interval describes a range of values compatible with an estimate under the statistical method used. It reflects sampling uncertainty, not the range of individual participant outcomes and not a guarantee that the true effect lies within the interval. For these comparisons, the recalculated intervals are unadjusted and compare each indirect-device mean with the Macintosh mean.

The Airtraq, Storz DCI, and McGRATH intervals lie entirely below zero. Their estimates are -0.8, -0.71, and -0.85, respectively. This indicates that the unadjusted intervals are consistent with lower mean coded grades in those groups than in the Macintosh group. The GlideScope estimate is -0.51, and its interval extends across zero; values on either side of no mean difference remain compatible with that comparison. This is consistent with its unadjusted p-value of 0.095.

Intervals do not address whether a difference is important in clinical practice. The registry record does not report a threshold for a meaningful difference in coded grade. Precision is also affected by how the ordinal grades are represented as numeric values and by the unadjusted nature of the comparisons. The intervals do not correct for testing multiple devices, and they do not describe category-specific probabilities. No confidence intervals for the individual grade distributions are posted in the registry record.

The estimates and intervals summarize uncertainty in group averages; they do not establish that the same pattern would occur in other patient groups or settings. Their interpretation is limited to the participants and outcome summaries in the registry record.

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 figures are planning illustrations for two-group comparisons, not the trial’s original design calculations. For this continuous outcome, the figures are participants per arm, not total events. The calculations assume a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. They use the observed effect or a stated fraction of that effect as the effect to detect. The trial’s original sample-size assumptions are not reported in the registry record.

The 80% power column gives the illustrative number of participants per arm for a design that would have an 80% chance of detecting the assumed effect under the calculation’s assumptions, if that effect were the true one. The 90% power column gives the corresponding planning number for a higher target chance of detection. These are design targets, not observed trial results, and they do not show the probability that a particular finding is true.

Each comparison has planning rows for 100%, 75%, and 50% of the observed effect. Smaller effects require more participants for the same target power. For example, the Airtraq illustration lists 50 participants per arm for 80% power at 100% of the observed effect, 88 at 75%, and 198 at 50%. The values differ across device comparisons because the observed effect estimates differ.

These calculations are not observed power. They are hypothetical planning estimates that rely on the stated assumptions and observed effect estimates; smaller effects require larger planned groups. They should not be read as evidence that the completed study did or did not have adequate power for its original research question.

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 = -0.800; pooled standard deviation σ = 1.420.
2. n = 2 × (1.96 + 0.842)² × 1.420² / -0.800² = 49.5, rounded up to 50 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 <- -0.8                      # observed difference in means
sigma <- 1.42042247236518                     # 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(602979)
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 = 50 (80% power), 67 (90% power)
 75% of observed effect: n per arm = 88 (80% power), 118 (90% power)
 50% of observed effect: n per arm = 198 (80% power), 265 (90% power)
power.t.test: 50.5 
Simulated power at n = 50 per arm: 0.793 (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 one primary outcome measure and no posted secondary outcome measures. At the same time, the primary comparison involves four indirect devices against one Macintosh control, producing multiple pairwise comparisons. The posted recalculations are unadjusted. Whether the trial protocol specified a hierarchy, an adjustment for multiple testing, or a single primary contrast is not reported in the registry record. Consequently, the listed p-values do not account for the fact that several device comparisons are being considered together.

Missing-data procedures are not reported. The primary outcome summaries give 45 participants in each device arm, whereas the adverse-event summaries list 48 participants at risk per arm; the record does not explain these differing figures. It does not state whether all randomized participants were included in the outcome summaries, whether any observations were missing, or how missing observations were handled. The registry enrollment entry is 240, and no explanation is given for its relationship to the posted outcome and safety denominators.

The analysis populations are not reported. The registry does not specify whether the comparisons followed an intention-to-treat approach, included only participants who received the assigned device, or used another population definition. It also does not report a statistical analysis plan, prespecified covariates, adjustment for baseline characteristics, or any interim analyses. These matters cannot be inferred from the randomized, parallel-group design or from the summary statistics.

As a general statistical consideration, missing outcomes can affect both the estimated group means and the uncertainty around those means, especially if missingness is related to the outcome or differs between groups. Without counts and handling rules, the extent and direction of any such effect cannot be assessed. Similarly, absence of a reported multiplicity method is not evidence that none was used; it means that the registry record does not document one.

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 2% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: corneal laceration (2.1%), iliac vein rupture (2.1%), right tonsillar pillar laceration (2.1%).

The safety summaries list 48 participants at risk for serious adverse events in each of the five device groups. Serious adverse events are reported for 2 participants in the Macintosh group and 1 in the McGRATH group; none are listed for Airtraq, Storz DCI, or GlideScope. The summaries report 0 deaths in every group.

For other adverse events, the record lists 0 affected participants in the Macintosh, Airtraq, Storz DCI, and GlideScope groups, and 1 in the McGRATH group. These are the recorded group counts; they should not be interpreted as complete estimates of comparative safety without more information about event collection and follow-up.

The registry lists Corneal Laceration, Iliac Vein Rupture, and Right Tonsillar Pillar Laceration among the serious adverse-event terms, each at 2.1%. It does not link these terms to particular device groups in the posted summary. The safety record does not provide event-level narratives, timing, severity beyond the serious classification, or an analysis comparing groups. The adverse-event denominators also differ from the participant counts in the primary outcome summaries, and the reason is not reported in the registry record.

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

The posted primary-outcome summaries show lower average coded grades in each indirect-device group than in the Macintosh group. The unadjusted mean differences are negative for all four comparisons. The intervals for Airtraq, Storz DCI, and McGRATH lie below zero, while the GlideScope interval includes zero. These results describe the posted group averages and their uncertainty under simple unadjusted comparisons.

They do not show that every participant had a better view with an indirect device, or reveal the proportion of participants in each easy, restricted, or difficult category. The endpoint is an ordered classification summarized as a mean, and the registry does not report a clinically meaningful threshold for the differences. The estimates therefore do not by themselves indicate how consequential a change in coded grade would be.

The findings also do not establish effects on successful intubation, number of attempts, time elapsed, physiological stress, or complications. Those outcomes appear in the registry’s description of the motivation for the study, but they are not posted secondary outcome measures in this record. Nor do the safety summaries establish that one device is safer than another: they provide limited event counts without a comparative safety analysis or detailed event attribution.

Finally, these data concern the randomized study population and the outcome summaries recorded for it. The registry record does not give enough information to assess missing outcomes, analysis populations, multiplicity handling, or generalizability to other clinical settings. The appropriate statistical reading is therefore specific: the posted mean-grade comparisons favor lower numeric grades in the indirect-device groups, with differing precision, while broader conclusions are not supported by these results alone.

16. Why This Trial Matters Statistically

This trial raises several statistical issues that are common when clinical outcomes are naturally categorical but are reported using numeric summaries. The laryngeal-view endpoint has ordered grades and clinically described groupings, yet the posted results use means and standard deviations. That makes the results compact and permits mean comparisons, but it leaves unanswered whether the category distributions differ in ways that the averages conceal.

The study also compares four devices with a single control. Multiple comparisons call for clear reporting of the prespecified primary contrast and how the family of tests was handled. The registry contains unadjusted recalculations for each comparison, but does not report a multiplicity plan. This distinction matters because nominal p-values do not communicate the uncertainty introduced by considering several comparisons together.

Precision deserves attention alongside statistical significance. The estimated differences are all negative, but the GlideScope interval includes zero while the other three intervals lie below zero. This makes clear why an estimate, its interval, and the design context should be considered together rather than relying on a single threshold or ranking devices by the means alone.

The record further illustrates the importance of transparent denominators and analysis populations. It lists enrollment of 240, outcome summaries with 45 participants per arm, and adverse-event summaries with 48 at risk per arm, without explaining the differences. Clear accounting of randomized participants, analyzed participants, missing outcomes, and safety follow-up is necessary for readers to judge how completely the results represent the trial.

These considerations do not invalidate the posted summaries. They define what can be learned from them and what additional reporting would be needed for a fuller assessment.

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 main trial-specific limitation in the registry record is the gap between the outcome’s categorical definition and its presentation as a mean and standard deviation. The grade coding is ordered, but the record does not establish equal spacing between categories or provide the number of participants in each category. As a result, the reported averages do not show the full distribution of views.

The primary outcome title refers to a percentage distribution, while the posted results are group means and standard deviations. The record does not explain this difference or post the grade-specific percentages. It also does not report the actual number of participants with each grade, a clinically meaningful threshold, or secondary measures such as intubation success and attempts.

There is incomplete accounting of participants across the record: enrollment is listed as 240, primary-outcome summaries give 45 participants per arm, and adverse-event summaries list 48 at risk per arm. The registry does not explain these denominators or identify the analysis populations. Missing-data handling, adherence, and participant flow are not reported.

Further limitations include absent details about the single-masking procedure, randomization implementation, prespecified statistical plan, multiplicity control, and interim analyses. The comparison p-values are unadjusted recalculations, and no adjusted analysis is reported. The adverse-event summary supplies limited counts and terms without linking the listed serious-event terms to specific groups. Together, these omissions restrict assessment of the robustness and scope of the results.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Comparison Study in Adult Surgical Patients of 5 Airway Devices — NCT00602979.
• Registry record last updated 2017-05-19; status last verified 2017-04.
• Results first posted 2017-05-19.
• 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

The registry describes a completed, prospective, randomized, single-masked, parallel-group comparison of Macintosh, Airtraq, Storz DCI, GlideScope, and McGRATH laryngoscopes in adult elective surgical patients. Enrollment is listed as 240; the primary outcome summaries report 45 participants per arm, and safety summaries list 48 at risk per arm.

The primary measure is the Cook-modified Cormack-Lehane laryngeal-view grade. Posted group means are lower in each indirect-device arm than in the Macintosh group. Unadjusted recalculated intervals lie below zero for Airtraq, Storz DCI, and McGRATH, while the GlideScope interval includes zero. The record does not report grade-specific distributions, secondary outcomes, missing-data methods, analysis populations, or multiplicity handling.