Learning Direct Laryngoscopy Using a McGrath Video Laryngoscope as Direct Versus Indirect Laryngoscope: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Learning Direct Laryngoscopy Using a McGrath Video Laryngoscope as Direct Versus Indirect Laryngoscope (NCT03471975), a randomized na study. The primary outcome is Intubation Success Rate.

2. Clinical Question

3. Trial Design

The registry describes a prospective, randomized trial with a parallel-group design. The enrollment field is 37. Participants were assigned to training with the McGrath video laryngoscope used either as a direct laryngoscope or with its video function. The direct-laryngoscope arm is identified as the control; the video-laryngoscope arm is the comparison group. The record lists single masking, but does not identify who was masked or how masking was implemented. Allocation concealment and the sequence-generation method are not reported in the registry record.

The study is marked completed. Its recorded start date is 2018-03-12 and primary completion date is 2018-07-09. The phase field is listed as NA. The sponsor is Ajou University School of Medicine. The listed conditions are airway management, endotracheal intubation, and medical education.

The training contrast concerns who can see the monitor during instruction: only the trainer in the direct-laryngoscope arm, and both trainer and trainee in the video-laryngoscope arm. Both groups are described as using the McGrath device; the registry distinguishes how it is used for teaching. The posted primary outcome is the number of participants with successful intubation using a direct laryngoscope on a manikin, with a timeframe of up to 10 minutes.

Further details about training duration, instructional content, trainer consistency, trainee experience, manikin conditions, and whether assessment was conducted by a masked evaluator are not reported in the registry record. The registry's own design rationale and original sample-size assumptions are also 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.

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 Intubation Success Rate, measured over up to 10 minutes.

The primary endpoint is intubation success rate, recorded as the number of participants who achieved successful tracheal intubation using a direct laryngoscope on a manikin. The assessment timeframe is up to 10 minutes. The arm values are 14 participants with success out of 17 in the Direct Laryngoscope arm, and 14 out of 20 in the Video Laryngoscope arm. These values describe performance after the two different teaching approaches; the endpoint itself assesses direct-laryngoscope intubation on a manikin.

A binary success outcome is commonly used because it gives a straightforward account of whether a specified task was completed under the assessment conditions. That is a general statistical rationale, not additional information about the investigators’ endpoint-selection process. In this study, the endpoint is relevant to the training question because it measures a practical intubation task after instruction. Its interpretation is bounded by the assessment setting: manikin performance is not the same outcome as intubation in clinical care, and the registry does not report whether other aspects of performance, such as time within the allowed period or procedural quality, were incorporated into the success definition.

The detailed success criteria, handling of attempts that were incomplete or technically difficult, and any evaluator procedures are not reported in the registry record. The endpoint therefore supports interpretation of the posted count and risk comparison, but does not establish how success was operationally defined beyond the registry description.

7. Results Posted in the Registry

• Video Laryngoscope: 70.0% (14/20) versus 82.4% (14/17) on control; risk difference -12.4 percentage points (95% CI -39.4 to 14.7), risk ratio 0.85 (0.59–1.22); unadjusted two-proportion z-test p = 0.383.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is binary at the participant level: a participant either meets the recorded definition of intubation success or does not. For such an outcome, the number with success and the number assessed in each arm provide the basic information needed to describe each arm. The registry reports 14 successes among 17 participants in the Direct Laryngoscope arm and 14 among 20 in the Video Laryngoscope arm. The posted proportions are 0.824 and 0.7. The registry does not describe the handling of participants without an evaluable outcome, so these arm counts should be interpreted as the posted denominators rather than as evidence about any unreported missing-data procedure.

What does the risk difference express?

A risk difference subtracts the comparator arm’s event proportion from the intervention arm’s event proportion. It remains on the probability scale: zero denotes equal observed proportions, while a positive or negative value indicates which arm has the higher observed proportion under the chosen comparison order. Here the reported risk difference is -0.123 for Video Laryngoscope relative to Direct Laryngoscope. The calculation method and confidence-interval method are not reported in the registry record. The estimate is unadjusted, and the registry does not report a model that accounts for participant or training characteristics.

How do risk ratios and odds ratios differ?

A risk ratio compares the proportions with the event in the two arms by division; an odds ratio compares the odds of the event. Both are relative measures, whereas the risk difference is an absolute measure on the event-proportion scale. Their values depend on the outcome and arm ordering, so the direction must be interpreted with the stated comparison in mind. The registry reports a risk ratio of 0.85 with interval 0.592 to 1.22, and an odds ratio of 0.5 with interval 0.104 to 2.407. These measures do not replace the arm counts or the risk difference; they give alternative descriptions of the same binary comparison.

What does a p-value convey?

A p-value describes how compatible the observed data are with a specified null model, subject to the statistical test and its assumptions. It is not the probability that the null hypothesis is true, and it does not quantify the size or practical importance of an effect. The posted unadjusted p-value is 0.383. The test, null-model details, and any prespecified decision rule are not reported in the registry record. For that reason, the p-value cannot by itself supply missing analysis details or determine the interpretation of the result.

Why consider an interval as well as an estimate?

An interval gives a range of values that are compatible with the data under the method used to construct it. A narrow interval indicates greater precision than a wide interval, all else equal. The interval for the risk difference is -0.394 to 0.147, spanning zero and values on either side. The interval level and construction method are not reported in the registry record. General statistical interpretation treats an interval as a measure of uncertainty, not as a guarantee that the true value lies within its endpoints.

What is not specified about the analysis?

The registry record lists no analyses in its analyses field, although it does post a comparison for the primary outcome. The statistical test, analysis population, covariate strategy, treatment of missing outcomes, and any sensitivity analyses are not reported in the registry record. Randomized allocation describes how participants were assigned, but does not by itself specify how outcomes were analyzed. Likewise, the masking designation is single, but who was masked and whether outcome assessment was masked are not stated. These omissions limit assessment of the assumptions and implementation behind the numerical comparison.

For a binary outcome, the usual comparison presumes that the participant-level outcome is classified consistently across arms and that the denominators represent the intended analysis population. General statistical practice also considers whether observations are independent and whether the model is appropriate for the data. The registry does not report enough detail to assess these issues for this trial. No additional statistical test or model should be inferred from the estimates alone.

10. Confidence Intervals and Precision

The point estimate for the risk difference is -0.123, and its reported interval extends from -0.394 to 0.147. The interval includes zero and also includes values on either side of zero. This means the observed data do not pin down the direction of the underlying difference with high precision: the plausible range under the interval method includes a lower success proportion in the video-laryngoscope training arm, little or no difference, and a higher success proportion. The interval is broad relative to the point estimate, so the estimate is uncertain.

The relative measures are also imprecise. The risk ratio is 0.85 with interval 0.592 to 1.22. The odds ratio is 0.5 with interval 0.104 to 2.407. Both intervals include the value corresponding to no relative difference. Because odds ratios and risk ratios have different scales, their estimates should not be compared as though they meant the same quantity. All of these results are based on the arm counts recorded for this trial.

A confidence interval is generally a range generated by a statistical procedure intended to reflect sampling uncertainty. That is a general explanation; the registry record does not report the confidence level or the method used to construct the intervals. The interval endpoints should therefore be understood as the posted uncertainty summaries, without assuming unreported methodological details.

Precision is distinct from whether an estimate is favorable or statistically persuasive. Even if the point estimate were taken at face value, its uncertainty matters: the posted data allow a substantial range of possible differences. The results do not establish equivalence, since no equivalence margin or equivalence analysis is reported. Nor does an interval spanning zero prove that the arms are identical. It indicates that the observed comparison is not precise enough to rule out differences in either direction under the reported interval.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total events. They are illustrations calculated from the observed effect, rather than the trial’s original design assumptions. The listed assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, a normal approximation, and an effect to detect set to the stated fraction of the observed effect. The registry’s own sample-size justification and original design assumptions are not reported in the registry record.

For planning at 100% of the observed effect, the figures are 186 participants per arm for 80% power and 248 participants per arm for 90% power. At 75% of the observed effect, the figures are 316 participants per arm for 80% power and 422 participants per arm for 90% power. At 50% of the observed effect, the figures are 676 participants per arm for 80% power and 904 participants per arm for 90% power.

In plain terms, the 80% power column gives an illustrative arm size for a design with an 80% chance of detecting the specified effect under the stated assumptions; the 90% power column gives an illustrative arm size for a higher chance under those same assumptions. Detecting a smaller effect requires more participants, which is why the planning figures rise as the assumed fraction of the observed effect decreases. These are planning illustrations, not observed power.

The figures depend on the observed effect used as their starting point. If that estimate is uncertain, the resulting planning values are uncertain as well. They should not be read as a retrospective judgment about whether the completed trial was adequately designed, because the trial’s original design assumptions are not reported.

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 = 0.824; treatment proportion p₁ = 0.700; average p̄ = 0.762.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.6025 = 1.1808.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.5961 = 0.5017.
4. n = (1.1808 + 0.5017)² / (-0.1235)² = 185.5, rounded up to 186 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 <- 0.823529411764706                          # control proportion
p1 <- 0.7                          # 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(3471975)
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 = 186 (80% power), 248 (90% power)
 75% of observed effect: n per arm = 316 (80% power), 422 (90% power)
 50% of observed effect: n per arm = 676 (80% power), 904 (90% power)
power.prop.test: 185.5 
Simulated power at n = 186 per arm: 0.803 (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 2 outcome measures and no posted secondary outcomes. The primary outcome is intubation success rate on a manikin using a direct laryngoscope, assessed up to 10 minutes. The record does not provide enough detail to determine whether other outcomes were collected but not posted, or how the listed outcome measures relate to the endpoint description. The registry’s analyses field lists 0 analyses, while a primary-outcome comparison is posted.

Multiplicity arises when several outcomes, time points, treatment contrasts, or subgroup comparisons are tested. Repeated testing can increase the chance of finding an apparently unusual result by chance. That is a general statistical concern. The registry record does not report a multiplicity strategy, a hierarchy among outcomes, or an adjustment to account for multiple comparisons. With no posted secondary outcomes, the extent of any multiplicity in the trial’s full analysis cannot be determined from the record.

Missing-data handling is not reported in the registry record. The posted primary outcome gives arm denominators of 17 and 20, but does not state whether all randomized participants had evaluable outcomes, whether any outcomes were missing, or how any missing values were handled. The record also does not report whether the analysis followed intention-to-treat, per-protocol, or another analysis population. The registry’s enrollment field is 37, but that field alone does not specify the analyzed population or the flow of participants through the trial.

No covariate-adjusted analysis, imputation procedure, sensitivity analysis, or subgroup analysis is reported. Nor does the record describe whether participants were excluded after randomization, or how deviations from the assigned training were handled. These details matter because analysis choices can affect the estimated comparison, particularly when outcomes are unavailable or participants do not follow the assigned approach. The posted counts and estimates can be described as recorded, but the absent information prevents a fuller assessment of analysis populations and robustness.

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 reports serious adverse events for 0 of 17 participants at risk in the Direct Laryngoscope arm and 0 of 20 at risk in the Video Laryngoscope arm. It also reports other adverse events for 0 of 17 and 0 of 20, respectively. Deaths are recorded as 0 in both arms. These are the registry’s posted figures; they describe events reported within the record, not proof that no event of any kind occurred.

The adverse-event reporting period, event definitions, collection procedures, and criteria for judging seriousness are not reported in the registry record. The listed groups and at-risk figures therefore cannot establish how actively events were sought or which events were within scope. The record also does not report details of non-serious events beyond the posted zero counts.

Zero reported events in these arm records should be interpreted in the context of the study’s size and setting. They do not demonstrate that either training approach is risk-free, and the trial’s manikin-based training outcome is not a comprehensive assessment of clinical safety. No medical conclusion or advice follows from these registry entries alone.

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

The posted results describe a randomized comparison of two ways of teaching tracheal intubation with the McGrath device. In one arm, only the trainer could see the monitor; in the other, both trainer and trainee could see it. The primary assessment was successful use of a direct laryngoscope on a manikin up to 10 minutes. The result is therefore about performance on that specified task after the training contrast, not about all aspects of learning or clinical airway management.

The observed success proportions were 0.824 for the Direct Laryngoscope arm and 0.7 for the Video Laryngoscope arm. The risk difference was -0.123 for Video Laryngoscope relative to Direct Laryngoscope, with a reported interval from -0.394 to 0.147 and an unadjusted p-value of 0.383. The interval spans zero and both directions, so the estimate is uncertain. The registry record does not report the test or a prespecified decision threshold for this comparison.

The findings do not establish that the training approaches are equivalent. Equivalence would require a prespecified margin and an analysis designed to assess whether the difference lies within that margin; these are not reported. The findings also do not establish that one method is better, worse, or interchangeable in settings beyond the manikin assessment. A nonzero estimate does not by itself demonstrate a meaningful or reproducible effect.

Important context is absent, including learner experience, training duration and content, detailed success criteria, outcome-assessment procedures, missing-data handling, and the original sample-size rationale. The record does not describe whether trainee performance was assessed by a masked evaluator. Those gaps limit both causal interpretation and generalization. The safest statistical reading is confined to the posted arm counts and unadjusted comparison, with the uncertainty reflected in the reported interval.

16. Why This Trial Matters Statistically

This trial poses a useful statistical question about a specific instructional contrast: whether learners’ access to a monitor during teaching is associated with a difference in subsequent manikin intubation success. The endpoint is binary and practical, making the arm counts and risk difference relatively direct to interpret. The result also illustrates why an effect estimate should be read together with its uncertainty rather than reduced to a yes-or-no label.

The observed risk difference is -0.123, but its reported interval, -0.394 to 0.147, spans zero and values in both directions. The unadjusted p-value is 0.383. The discrepancy between a point estimate and a wide uncertainty range is an important teaching example: a sample can yield a numerical difference without precisely establishing its direction or size. The registry’s reported risk ratio and odds ratio likewise have intervals that include values compatible with no relative difference.

The sample-size illustrations further show a general design principle: planning to detect smaller effects requires more participants under a fixed set of assumptions. The figures are illustrative and are based on the observed effect, not the original trial plan. They therefore help explain design sensitivity but do not answer whether the trial’s actual design matched its objectives.

The record also demonstrates why transparent methods reporting matters. Details about masking, outcome criteria, missing data, analysis populations, multiplicity, and the statistical test are absent. Without those details, readers can interpret the posted estimates but cannot fully evaluate how the analysis was conducted. The study is educationally relevant as a focused comparison, while its registry record supports a cautious interpretation bounded by the manikin endpoint and the precision of the estimates.

17. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The primary endpoint is measured on a manikin, and the registry does not report patient-based performance. Results on this task should not be treated as direct evidence about outcomes in clinical intubation. The endpoint description states success using a direct laryngoscope, but the detailed success criteria and assessment procedures are not reported in the registry record.

The registry identifies the design as single-masked but does not say who was masked. It does not state whether outcome assessors were masked to training assignment. Since the arms differ in who could see the monitor during instruction, details of how the subsequent assessment was standardized would be useful, but are not reported. Information about trainee experience, training duration, instructor consistency, and any practice before assessment is also not reported in the registry record.

The posted comparison is unadjusted, and the statistical test and interval-construction method are not specified. The record does not describe missing outcomes, analysis populations, protocol deviations, or sensitivity analyses. It also does not report the original sample-size justification or any prespecified analysis plan. These omissions make it difficult to assess the robustness of the result or the extent to which analytic decisions were prespecified.

The interval around the risk difference is broad and crosses zero, so the estimated contrast is imprecise. The sample-size planning figures are retrospective illustrations based on the observed effect and cannot replace a documented original design rationale. The registry does not report enough information to assess generalizability beyond the learners and training conditions studied. These limitations are specific to the available trial record and do not establish that unreported procedures were or were not performed.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Learning Direct Laryngoscopy Using a McGrath Video Laryngoscope as Direct Versus Indirect Laryngoscope — NCT03471975.
• Registry record last updated 2019-08-19; status last verified 2019-07.
• Results first posted 2019-08-19.
• 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

NCT03471975 is a completed, prospective randomized parallel-group trial sponsored by Ajou University School of Medicine. The registry describes training with the McGrath video laryngoscope used as a direct laryngoscope versus with its video function, where both trainer and trainee could see the monitor. It lists single masking but does not identify who was masked.

The primary outcome is intubation success using a direct laryngoscope on a manikin, assessed up to 10 minutes. The posted counts are 14 of 17 in the Direct Laryngoscope arm and 14 of 20 in the Video Laryngoscope arm. The risk difference is -0.123, with a reported interval of -0.394 to 0.147; the unadjusted p-value is 0.383. The interval includes zero and permits differences in either direction.

The registry does not report the statistical test, analysis population, missing-data procedures, multiplicity approach, or original sample-size rationale. The outcome is a manikin measure, and the record does not establish how results generalize to clinical performance.