GlideScope Versus Direct Laryngoscope for Emergency Intubation: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for GlideScope Versus Direct Laryngoscope for Emergency Intubation (NCT01235065), a randomized na study. The primary outcome is Number of Participants Who Survived to Hospital Discharge.

2. Clinical Question

3. Trial Design

The registry describes a randomized, parallel-group trial with no masking. A total enrollment of 623 is recorded. The direct laryngoscope arm included 320 participants, and the video laryngoscope arm included 303 participants. The study is marked completed. Its start is recorded as 2008-07, and its primary completion date is 2016-11-16. The sponsor is the University of Maryland, Baltimore. The phase is listed as NA.

The two arms represent different laryngoscopy techniques for emergency intubation: direct laryngoscopy and video laryngoscopy. The study purpose specifically names a GlideScope video laryngoscope and a Macintosh direct laryngoscope. Random allocation is intended to make the groups comparable on average at the point of assignment, although the registry record does not report details of sequence generation, allocation concealment, or implementation. Those details should not be inferred from the randomized label alone.

The registry record lists two outcome measures and one secondary outcome, length of time to perform the intubation procedure. The primary outcome is survival to hospital discharge. There are no posted analysis records. The record does not report the protocol’s original sample-size assumptions, its planned statistical analysis, or whether any interim analyses were intended. The planning illustration associated with the posted results is separate from those original design details.

Because masking is listed as none, the trial is described as unmasked. The registry does not explain whether participants, clinicians, or outcome assessors were masked, or how the absence of masking was implemented. Hospital-discharge survival is a relatively direct outcome, but information on ascertainment procedures is not reported in the registry record. These design features limit what can be established from the registry alone about conduct and outcome assessment.

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 Who Survived to Hospital Discharge, measured over 2 weeks, on average.

The primary endpoint counts participants who were discharged alive from the study center. Its timeframe is recorded as 2 weeks, on average. In the direct laryngoscope group, 296 of 320 participants were recorded as surviving to hospital discharge; in the video laryngoscope group, 275 of 303 were recorded as surviving.

A binary endpoint records whether each participant experienced a defined outcome, rather than measuring a continuous quantity such as a duration or score. Counting survival to discharge gives a clinically interpretable summary of the outcome for each randomized group. Comparing the proportions allows the registry results to express the difference between groups on an absolute scale, in percentage-point terms when expressed as percentages. The posted estimate uses a risk-difference scale, with the video group compared with the direct laryngoscope group.

Hospital-discharge survival was selected as the primary outcome in this study, but the reason for that choice and the endpoint definition beyond the registry description are not reported in the registry record. The average timeframe does not establish the exact follow-up time for every participant. The record does not describe how participants without a recorded discharge status were handled, nor does it report a separate analysis population for this endpoint. Interpretation therefore depends on the posted counts and comparison, while additional outcome-collection and missing-data details remain unknown.

7. Results Posted in the Registry

• Video Laryngoscope: 90.8% (275/303) versus 92.5% (296/320) on control; risk difference -1.7 percentage points (95% CI -6.1 to 2.6), risk ratio 0.98 (0.94–1.03); unadjusted two-proportion z-test p = 0.432.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is binary: each participant either survived to hospital discharge or did not. For a binary outcome, a group’s risk is the number with the event divided by the number assessed in that group. The posted proportions are 0.925 in the direct laryngoscope group and 0.908 in the video laryngoscope group. The registry also reports the event counts and group sizes: 296 of 320 and 275 of 303, respectively. These values describe the observed groups; they are not adjusted for other characteristics in the information posted.

The principal comparison is a risk difference, calculated in the posted analysis as video-group risk minus direct-group risk. Its estimate is -0.017. A risk difference is an absolute contrast: zero means equal risks, a negative value means a lower observed risk in the video group, and a positive value means a higher observed risk in that group. The estimate’s direction is descriptive, while uncertainty is conveyed by its reported interval. No additional calculation is needed to interpret that orientation.

A confidence interval gives a range of values compatible with the data under the method’s assumptions. Its endpoints are -0.061 and 0.026 for the risk difference. Because zero lies within that range, the interval does not rule out no difference on this scale. It also includes values on both sides of zero. The confidence level and the precise method used to calculate the interval are not reported in the registry record, so those methodological details should not be assumed.

The registry reports a p-value of 0.432 for the unadjusted comparison. In general, a p-value is calculated under a null model, commonly a model of no group difference, and quantifies how compatible the observed data are with that model. It is not an effect-size measure and does not measure the probability that the null model is true. The particular test and its assumptions are not reported in the registry record. Nor is a trial-specific threshold for statistical significance reported.

The risk ratio and odds ratio are alternative relative scales. The risk ratio estimate is 0.981, with reported interval endpoints of 0.936 and 1.029. It compares the group risks directly; a value of 1 is the no-difference value. The odds ratio estimate is 0.796, with interval endpoints of 0.451 and 1.407. It compares odds rather than risks, and 1 is also its no-association value. Both reported intervals include 1. These scales can be useful for different statistical purposes, but the odds ratio is not interchangeable with an absolute risk difference. The registry does not report the methods used for either relative measure.

Randomization is a design feature intended to support a fair comparison by assigning participants to groups by chance. It does not, on its own, reveal whether allocation was concealed or whether the groups were analyzed as randomized. Those operational and analysis details are not reported in the registry record. The trial is listed as parallel and unmasked, but the record does not describe the masking status of specific roles or the analytic approach used to account for assignment.

In general, an unadjusted comparison contrasts the outcome data between groups without accounting for other measured covariates in a regression model or other adjustment procedure. The posted effect is identified as unadjusted. No adjusted estimate or model specification is reported. Whether adjustment was planned, and whether other analytic methods were used, is not reported in the registry record.

General statistical context: the precision of an estimate depends on the amount of information in the data and the variability of the outcome. For a binary endpoint, the number of participants and the event proportions contribute to that information. A wider interval indicates less precision than a narrower interval, but does not by itself tell whether a result is important. General methods such as regression adjustment, stratification, or robust variance estimation can address particular features of a design or data structure, but the record does not report that any such method was used.

There are 0 analysis records listed in the registry, despite the posted comparison statistics. This means the registry record does not provide a corresponding analysis entry with details such as a named test, model, analysis population, or prespecified adjustment variables. It does not establish whether analyses were or were not conducted outside the posted registry information. The posted estimates can be interpreted as numerical results while recognizing that the details necessary to reproduce their derivation are not reported.

10. Confidence Intervals and Precision

The risk-difference estimate is -0.017, and its reported interval runs from -0.061 to 0.026. The interval includes zero, the value representing equal risks on the risk-difference scale. It also includes negative and positive differences. Thus, the point estimate alone gives only one central value, while the interval communicates that the data are compatible with a range of group differences in either direction.

Precision concerns how narrowly an estimate is bounded, not whether a result is important or whether a treatment should be used. A narrower confidence interval would indicate that the data constrain the estimate to a smaller range, assuming the same method and confidence level. The registry does not state the confidence level or the interval calculation method, so the interval should be described by its posted endpoints rather than by an assumed level.

The relative-effect intervals also span their no-difference values. The risk ratio is 0.981, with interval endpoints 0.936 and 1.029; its reference value is 1. The odds ratio is 0.796, with endpoints 0.451 and 1.407; its reference value is also 1. These measures reinforce that the posted data leave uncertainty about direction and magnitude, though each scale has a different interpretation.

Observed counts help show the amount of outcome information: 296 of 320 participants in the direct group and 275 of 303 in the video group were recorded as surviving. Counts alone do not reveal how missing outcome information was handled. Missingness details and an analysis population are not reported in the registry record. The interval’s interpretation therefore depends on the assumptions of the calculation and the completeness and classification of endpoint data, details that are not available in the 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 planning figures are participants per arm, not total events. They are illustrative calculations based on the observed effect, not the trial’s original design assumptions. The 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 to the stated fraction of the observed effect. The trial’s own original sample-size justification and design assumptions are not reported in the registry record.

The 80% power column gives the illustrative number of participants per arm for 80% power under those assumptions and for the specified effect size. In plain language, power is the probability that a statistical test will detect an effect of the chosen size if that effect is present and the assumptions hold. The 90% power column gives the corresponding participants per arm for 90% power, a higher planned probability of detecting the same effect under the same framework. These are planning concepts, not guarantees about what a future study would find.

For 100% of the observed effect, the illustration gives 3,972 participants per arm for 80% power and 5,316 for 90% power. For 75% of the observed effect, it gives 6,894 participants per arm for 80% power and 9,229 for 90% power. For 50% of the observed effect, it gives 15,135 participants per arm for 80% power and 20,260 for 90% power. Smaller effects require more participants to detect under the same assumptions, which is why the illustrative requirements increase as the target fraction decreases.

The visual planning curve represents the same relationship between the effect size being targeted and the number of participants required. These calculations use the observed estimate as a starting point, which is uncertain; they should not be read as proof that the observed effect is true or as a recommendation for a particular future design. This is not observed power. The registry does not report the trial’s original planning rationale, and these figures do not reconstruct it.

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 = 0.925; treatment proportion p₁ = 0.908; average p̄ = 0.916.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.3917 = 0.7676.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.3915 = 0.3295.
4. n = (0.7676 + 0.3295)² / (-0.0174)² = 3,971.3, rounded up to 3,972 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 <- 0.925                          # control proportion
p1 <- 0.907590759075908                          # 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(1235065)
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 = 3,972 (80% power), 5,316 (90% power)
 75% of observed effect: n per arm = 6,894 (80% power), 9,229 (90% power)
 50% of observed effect: n per arm = 15,135 (80% power), 20,260 (90% power)
power.prop.test: 3971.3 
Simulated power at n = 3,972 per arm: 0.795 (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 two outcome measures and identifies one secondary outcome: length of time to perform the intubation procedure. The primary outcome is survival to hospital discharge. It does not report whether other outcomes or subgroups were prespecified, how many statistical tests were planned, or whether any multiplicity adjustment was intended. Multiplicity refers, in general, to the increased chance of a false-positive finding when many hypotheses are tested. Whether that concern applies to any additional analyses in this trial cannot be determined from the registry record.

The posted p-value is unadjusted. The record does not report a family of hypotheses, a correction method, or a prespecified threshold for the primary analysis. It would therefore be inappropriate to imply that the posted comparison accounts for multiple testing, or to infer that no multiplicity plan existed. The statistical plan is not reported in the registry record.

The registry contains 0 analysis records. Although a primary comparison is posted, the record does not identify the analysis population, such as whether all randomized participants were analyzed in their assigned groups. It also does not state whether participants were excluded from the analysis or how exclusions would have been handled. The record does not describe whether an intention-to-treat, per-protocol, or another analysis population was used.

Missing outcome data can affect a binary-outcome comparison if survival status is unavailable for some participants. The posted counts give arm sizes and survival counts, but the registry record does not report whether all randomized participants had an observed endpoint, how missing values were treated, or whether sensitivity analyses were conducted. No imputation method or missing-data assumption is reported. These omissions do not establish that data were missing; they mean the registry record does not provide enough information to assess that issue.

In general, prespecified analysis methods help distinguish planned tests from analyses selected after outcomes are known, and multiplicity procedures can control error across a defined set of tests. Those are general statistical principles. The record does not provide enough detail to determine what methods were planned or applied in this trial, so conclusions about analysis populations, missingness, and multiplicity should remain limited to the posted information.

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 adverse-event figures list 320 participants at risk in the direct laryngoscope group and 303 at risk in the video laryngoscope group. For both groups, the posted counts for participants affected by serious adverse events are 0, and the counts for participants affected by other adverse events are also 0. No serious adverse-event terms are listed.

These entries describe what is recorded in the registry, not a complete account of every possible safety outcome. A zero count in a posted category means that no affected participants are recorded for that category; it does not by itself establish that no events occurred outside the categories, reporting period, or recording process. The registry record does not provide further details about event definitions, collection procedures, or the period covered by adverse-event monitoring.

Deaths are listed as null for both groups. This is not the same as a reported count of zero; deaths are not reported in that adverse-event entry. The primary endpoint does separately report participants who survived to hospital discharge, but it does not substitute for a detailed adverse-event summary. Safety interpretation is therefore limited to the posted event counts and the missing death entries.

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

The posted results describe survival to hospital discharge among participants randomized to direct or video laryngoscopy. The estimated risk difference is -0.017 for video compared with direct laryngoscope use, with a reported interval from -0.061 to 0.026. The interval crosses zero, and the unadjusted p-value is 0.432. These figures indicate uncertainty about the direction and size of the difference; they do not isolate a precise effect.

The data do not establish equivalence. Demonstrating equivalence or non-inferiority generally requires a prespecified margin and a design and analysis suited to that question. Such a margin and corresponding plan are not reported in the registry record. Likewise, the results should not be taken as proof that a difference exists: the interval includes zero, and the posted p-value does not provide strong evidence against a no-difference model under conventional interpretation.

The trial’s stated objective was to assess whether GlideScope video laryngoscopy was superior to direct laryngoscopy for definitive airway management in acutely injured patients. The available registry information permits a description of the posted primary outcome comparison, but it does not provide all details needed to evaluate the original hypothesis test, missing outcome handling, or analysis population. The primary result also does not answer questions about outcomes other than survival to hospital discharge. The listed secondary outcome is time to perform the intubation procedure, but its result is not included in the registry information.

These results should be understood as a comparison in the trial’s enrolled groups, not as a statement about every clinical setting or patient. Generalizability depends on eligibility criteria, clinical setting, implementation, and other study details, several of which are not reported in the registry record. No medical conclusion or treatment recommendation follows from the numerical comparison alone.

16. Why This Trial Matters Statistically

This trial illustrates why an observed difference and the uncertainty around it need to be read together. The risk-difference estimate is -0.017, but its interval, -0.061 to 0.026, includes zero and extends in both directions. A point estimate offers a compact summary; the interval shows that the data do not identify a narrow range confined to one direction. The unadjusted p-value of 0.432 adds a test-based summary, but it cannot replace the effect estimate or its uncertainty.

The comparison also shows how effect scales shape interpretation. The risk difference expresses an absolute contrast, while the risk ratio and odds ratio express relative contrasts. Their estimates and intervals are not interchangeable, and the odds ratio is not a direct measure of the absolute change in survival probability. Reporting multiple scales can help readers understand different aspects of a comparison, while the registry’s lack of analysis details means the methods behind the posted estimates cannot be fully assessed.

Randomized allocation is an important design feature, but it does not answer every statistical question. The absence of analysis records leaves the analysis population, handling of missing values, and prespecified approach to multiplicity unreported. These details matter because readers need to know which participants contributed to the estimate and what assumptions were used.

The planning illustration also highlights the relationship between a target effect and the amount of information needed to detect it. Smaller effects require more participants under the stated illustrative assumptions. Those planning calculations are distinct from the trial’s original design rationale and from the interpretation of its observed result. Keeping those distinctions clear prevents planning quantities from being mistaken for evidence about what the trial found.

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 record leaves important trial and analysis details unreported. It does not provide full eligibility criteria, a detailed account of the clinical setting, allocation concealment procedures, the randomization sequence method, or the roles covered by the unmasked designation. These omissions limit assessment of how the study was implemented and how directly its participants represent other settings.

The primary completion date and average timeframe are recorded, but individual follow-up duration and endpoint ascertainment procedures are not described. The record does not report missing outcome counts, the treatment of missing data, or the analysis population. It also does not provide the statistical test, confidence-interval method or confidence level, a prespecified significance threshold, or a detailed statistical analysis plan. The registry lists 0 analysis records, so the derivation of the posted comparison cannot be fully checked from an analysis entry.

Only one secondary outcome is identified, and its result is not included in the posted information described for this comparison. The record does not state whether other outcomes or analyses were planned, how multiple tests were handled, or whether interim analyses were conducted. Those matters are not reported in the registry record and should not be inferred.

Adverse-event entries show zero participants affected in the posted serious and other event categories, but deaths are null rather than reported as zero. Definitions, monitoring duration, and event collection methods are not detailed. Finally, the sample-size figures are planning illustrations based on the observed effect, not the original trial’s design justification. Together, these constraints mean the posted numerical results can be described, but fuller judgments about analytic robustness, safety reporting, and generalizability require information not reported in the registry record.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: GlideScope Versus Direct Laryngoscope for Emergency Intubation — NCT01235065.
• Registry record last updated 2023-06-01; status last verified 2018-06.
• Results first posted 2023-06-01.
• 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, unmasked, parallel-group study of emergency intubation using direct or video laryngoscopy. Enrollment was 623, with 320 participants in the direct laryngoscope arm and 303 in the video laryngoscope arm. The primary outcome was survival to hospital discharge, assessed over 2 weeks, on average.

The posted risk difference for video compared with direct laryngoscope use is -0.017, with an interval from -0.061 to 0.026 and an unadjusted p-value of 0.432. The interval includes zero. The record also identifies length of time to perform the intubation procedure as a secondary outcome, but no result for it is included in the information.

Analysis details, missing-data handling, and the original sample-size justification are not reported in the registry record. The planning figures are illustrative calculations based on the observed effect, rather than a description of the trial’s original design.