An MRI Study of the Sniffing, Neutral and Extended Head and Neck Positions: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for An MRI Study of the Sniffing, Neutral and Extended Head and Neck Positions (NCT05002790), a na na study. The primary outcome is Angle A Measured on MRI.

2. Clinical Question

3. Trial Design

This is a completed, single-group MRI study registered as NCT05002790. The registry lists an enrollment of 20 and describes one data collection group, with participants scanned by MRI and data collected and analysed together. The study is not described as a randomized comparison: allocation is listed as NA, and the registry record does not identify parallel intervention and control groups. Masking is listed as none.

The study focuses on three head and neck positions: sniffing, neutral and extended. The description states that each subject will undergo 3 MRI scans. Angle A is to be measured on each scan after all scans performed that day, by 2 investigators. The primary outcome definition identifies Angle A as the angle between the tracheal axis and laryngeal axis. Angles B, C, D and E are listed as secondary outcomes.

The study rationale concerns anatomical alignment relevant to videolaryngoscopy. Its background describes the traditional sniffing position and notes the authors' suggestion that videolaryngoscopy may involve a different head and neck position. The study therefore examines MRI measurements of axes, rather than reporting a comparison of intubation success, ease of tube passage, or other clinical outcomes.

The record lists a start date of 2021-08-05, a primary completion date of 2021-10-21 and a completed status. The registered design does not establish a randomized causal comparison among positions. Because the record does not report scan order, control of measurement conditions, or the analysis used to account for repeated scans within a person, these design details cannot be assessed from 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

Analysis population for the primary outcome, as defined in the registry: data from all participants was analysed

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 Angle A Measured on MRI, measured over Each subject will undergo 3 MRI scans. Angle A will be measured on each scan at the end of all the scans performed that day. The angles will be measured by 2 investigators..

The primary endpoint is Angle A measured on MRI, expressed in degrees. It is defined as the angle between the tracheal axis (TA) and laryngeal axis (LA). The registry describes a mean of a continuous measure, with standard deviation as the dispersion measure. Each subject was to undergo 3 MRI scans, with Angle A measured on each scan; 2 investigators were to measure the angles.

The endpoint is used to represent anatomical alignment across the sniffing, neutral and extended head and neck positions. The study rationale connects these axes with positioning for videolaryngoscopy. In statistical terms, an angle is a continuous measurement, so the mean can describe its central value and the standard deviation can describe how spread out measurements are around that mean. Neither summary alone shows how much individual measurements overlap between positions or how precisely a difference between positions has been estimated.

The registry record does not report the actual Angle A measurements, position-specific means or standard deviations, estimates of differences, or confidence intervals. It also does not describe how the two investigators' measurements were combined or whether agreement between investigators was evaluated. The endpoint is therefore defined, but its observed values and measurement reliability are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registered primary outcome is a continuous MRI measurement: Angle A, defined as the angle between the tracheal axis and laryngeal axis. The registry specifies a mean and standard deviation. These summaries answer different descriptive questions. A mean describes the central value of a set of measurements; a standard deviation describes their spread. The standard deviation is not the uncertainty in the mean and is not a confidence interval for a contrast between positions.

What would an estimate and confidence interval describe?

In general, a confidence interval describes uncertainty around an estimated quantity, such as a mean or a difference between conditions. Its width reflects both the amount of information and the variability in the data, as well as the method used to calculate it. A narrow interval indicates greater precision for that estimand than a wide interval. The registry record does not report confidence intervals for Angle A or contrasts among positions, so the precision of any positional differences cannot be assessed.

A statistical test and an effect estimate are also not interchangeable. A test result addresses how compatible the data are with a specified null hypothesis under a statistical model. An effect estimate describes the size and direction of the contrast on the measurement scale. A p-value, if reported, would not by itself show whether a difference was large enough to matter in practice. The registry record reports no test results or p-values for the primary outcome.

Why does the repeated measurement structure matter?

The registry says each subject will undergo 3 MRI scans and that Angle A will be measured on each scan. Measurements from the same subject are likely to share subject-specific features, so treating all scan measurements as independent observations could understate uncertainty. In general, repeated-measures methods account for dependence within a subject when estimating position effects and their uncertainty. Other valid approaches may be possible, depending on the data and the intended estimand. The registry record does not identify the analysis method, the scan order, or the way repeated measurements were handled.

The registry also states that 2 investigators will measure the angles. In general, multiple measurements can be combined or used to assess reproducibility, but the choice affects the meaning of the outcome and its uncertainty. A description of blinding, measurement procedures, adjudication, or agreement statistics is not reported in the registry record. It is therefore not possible to assess whether investigator measurement variability was incorporated into the analysis.

What do mean and standard deviation leave unanswered?

A mean and standard deviation can describe the distribution of a continuous outcome, but they do not reveal the full data pattern. They do not show whether values are skewed, whether there are influential observations, or how much individual measurements overlap between positions. In general, plots and diagnostic checks can help assess these features. The registry record does not report outcome values or analysis diagnostics. No assumption about the distribution of Angle A can be verified from the record.

Over-dispersion is a general concern when observed variability exceeds what a model assumes. For a continuous angle, the relevant issue would be whether the chosen model adequately represents the observed variability and dependence, rather than assuming that a particular over-dispersion problem occurred. The registry record does not report a model or diagnostic assessment, so neither the presence nor handling of such a problem can be determined.

How should planning calculations be understood?

The registry description of planning illustrations specifies a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect defined as a stated fraction of the observed effect. For non-time-to-event outcomes, the illustrations are described as participants per arm for 80% or 90% power; the time-to-event illustration uses a total number of events. These are planning assumptions, not findings from the MRI study. The record explicitly distinguishes them from the trial's own design.

Those assumptions describe a hypothetical two-arm calculation, whereas the MRI study is registered as a single group with repeated measurements across positions. The planning illustrations therefore should not be read as evidence that the MRI study was designed or analysed as a two-arm trial. A calculated sample-size illustration is not observed power, and it does not establish the precision achieved by the actual measurements. No sample-size justification or statistical analysis plan for this study is reported in the registry record.

Finally, the number of analysis records is 0, and the registry does not post numerical primary outcome results. That absence prevents checking the calculation method against reported estimates, evaluating uncertainty, or assessing whether the planned outcome analysis was carried out as intended.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Neutral Position", "Sniffing Position", "Extended Position")
n   <- c(20, 20, 20)
m   <- c(20.7, 10.8, 30)
sp  <- c(6.8, 6.9, 5.2)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Neutral Position  20  20.700  6.800  17.518  23.882
CARM  Sniffing Position  20  10.800  6.900  7.571  14.029
CARM  Extended Position  20  30.000  5.200  27.566  32.434

11. Multiplicity, Missing Data and Analysis Populations

The registry identifies Angle A as the primary outcome and lists angles B, C, D and E as secondary outcomes. Assessing several outcomes or several contrasts can create a multiplicity issue: in general, the more inferential questions considered, the greater the chance that at least one result may appear notable by chance if each is tested without adjustment. Whether adjustment is needed depends on the questions, testing hierarchy and analysis plan. The registry record does not report a multiplicity strategy, a hierarchy among secondary outcomes, or the statistical tests used.

Missing-data handling is not reported in the registry record. The record says that data from all participants were analysed, but it does not state whether every participant had usable scans and complete measurements for every position and outcome. It does not describe exclusions, incomplete scans, unavailable measurements, or methods for handling missing values. No pattern or amount of missing outcome data can therefore be assessed from the registry record.

The stated analysis population is data from all participants. The registry also lists an enrollment of 20, but does not provide a participant flow or a separate account of who contributed measurements to each outcome analysis. The record contains no analysis entries. It is consequently unclear whether the stated population description corresponds to a completed analysis of all enrolled participants, and whether all registered outcomes were analysed. The registry record does not report a prespecified analysis population beyond the statement that data from all participants were analysed.

12. 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 0 serious adverse events among 20 at risk, 0 other adverse events among 20 at risk, and 0 deaths. No serious adverse event terms are listed. These are the safety counts recorded for the data collection group.

Zero reported events in a registry entry should be read as a description of what was recorded, not proof that an event was impossible or that risk was absent. The counts do not show how events were defined, how actively they were sought, or the period over which safety was monitored. Those details are not reported in the registry record. The MRI study is an anatomical measurement study, and the listed counts do not provide a comparison between randomized treatment groups; the registry describes a single group.

These figures also do not address whether the study measurements were complete or whether participants experienced other outcomes that were not included in the adverse-event fields. The safety record therefore supports only a narrow statement: the registry lists no serious adverse events, other adverse events or deaths in the reported group.

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

The study asks a focused anatomical question: how Angle A, the angle between the tracheal and laryngeal axes, is measured on MRI in sniffing, neutral and extended head and neck positions. The registry record defines the endpoint, identifies the planned repeated scans and names the additional angles of interest. It also gives a completed status and an enrollment of 20.

What the record does not provide is the result needed to answer the positional question. There are no reported Angle A values, position-specific summaries, contrasts, confidence intervals or statistical test results. The registry record therefore does not establish which position produced a particular measured angle, how large any difference was, or how precisely it was estimated.

The study's stated objective is not the same as an observed finding. Saying that the study aimed to determine which position significantly improves Angle A does not establish that a significant difference was found. Nor can significance or practical importance be inferred from the completed status or from the fact that measurements were planned.

The outcome is anatomical, not a direct clinical endpoint. Even a clearly estimated difference in an angle would not alone demonstrate improved intubation performance or patient outcomes. The registry record does not report comparisons of intubation success, tube passage, complications, or other clinical consequences. The rationale connects positioning with videolaryngoscopy, but a proposed rationale is not evidence of a clinical effect.

The design also limits causal interpretation. A single-group assessment across positions is not a randomized comparison with a separate control group. The record does not state whether position order was randomized or otherwise controlled, nor does it describe the analysis of repeated measurements. Any interpretation of positional contrasts would depend on such design and analysis details. They are not reported in the registry record.

Accordingly, the most defensible conclusion is that the registry documents a completed MRI study intended to measure anatomical alignment across three positions, but does not report the numerical findings needed to assess the primary question. It neither establishes benefit nor establishes a lack of benefit for any position.

14. Why This Trial Matters Statistically

This study illustrates the distinction between measuring an anatomical feature and demonstrating a clinical effect. Angle A is a continuous MRI measurement intended to describe alignment between two axes. Such a measurement can help formulate a mechanistic question, but its relevance to a procedure depends on evidence connecting the measurement to procedural outcomes. The registry record does not report that connection.

The repeated scans also raise an important design issue. When several conditions are measured in the same subject, the data contain within-subject dependence. Analyses that respect that structure can use the paired information while estimating uncertainty appropriately; analyses that ignore it may misstate precision. The registry identifies repeated scans but does not report the method used to analyse them.

Measurement by 2 investigators makes reliability another relevant statistical question. Differences between investigators can contribute variability, and the approach used to combine or compare their readings affects interpretation. The record specifies who was to measure the angles but does not report investigator agreement or how measurement variability was handled.

Finally, this record shows why study completion and a well-defined endpoint are not substitutes for reported results. Without estimates and uncertainty, readers cannot assess the size, direction or precision of the positional differences. The registry record is informative about the question and measurement plan, but it does not provide the evidence needed to quantify the findings or connect them to clinical performance.

15. 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 limitation for interpretation is that numerical outcome results are not reported in the registry record. Although the primary endpoint and secondary angles are identified, the record gives no observed values, estimates of positional contrasts, confidence intervals or test results. Statistical significance, effect magnitude and precision therefore cannot be assessed.

The registry describes a single group and lists allocation as NA. It does not report randomized assignment to positions or a separate control group. It also does not state the order of the MRI scans or whether scan order was controlled. These omissions limit assessment of possible order effects and of the basis for interpreting differences across positions.

The study planned measurements by 2 investigators, but the registry record does not describe measurement procedures, investigator blinding, how readings were combined, or whether agreement was assessed. It also does not report the statistical method for repeated scans within a subject. These details matter to the reliability and uncertainty of the angle estimates.

Participant characteristics beyond the enrollment are not reported in the registry record. The record does not give a participant flow, the completeness of MRI measurements, or missing-data handling. It says data from all participants were analysed, but the number of analysis records is 0 and no numerical results are posted. The extent to which that population statement was implemented cannot be independently assessed from the registry record.

Finally, Angle A is an anatomical surrogate rather than a direct measure of intubation performance or patient outcome. The registry record does not report those clinical outcomes or an analysis linking them to MRI measurements. As a result, even a reported anatomical contrast would require separate evidence before being interpreted as a clinical effect.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: An MRI Study of the Sniffing, Neutral and Extended Head and Neck Positions — NCT05002790.
• Registry record last updated 2024-08-28; status last verified 2024-06.
• Results first posted 2024-08-28.
• 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.

19. Record Summary

NCT05002790 is a completed, single-group MRI study of sniffing, neutral and extended head and neck positions. The registry lists an enrollment of 20, with each subject planned to undergo 3 scans. The primary outcome is Angle A, the angle between the tracheal and laryngeal axes, measured by 2 investigators; angles B, C, D and E are listed as secondary outcomes.

Allocation is listed as NA and masking as none. The registry describes data from all participants as analysed together, but records no analysis entries. It does not report numerical outcome results, confidence intervals, statistical tests, missing-data handling or a multiplicity strategy. The registry lists 0 serious adverse events, 0 other adverse events and 0 deaths. The record defines the anatomical question and design, but does not provide results with which to assess positional differences.