The Natural History of Small Airways Physiology in Diseased and Healthy States: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Natural History of Small Airways Physiology in Diseased and Healthy States (NCT00677560), a registered phase not stated study. The primary outcome is FEV1.

2. Clinical Question

3. Trial Design

The registry describes a completed clinical study sponsored by Imperial College London, with an enrollment of 126. The recorded start date is 2010-06-22 and the primary completion date is 2013-07-10. The status is completed. These details describe the registry record; they do not establish how many participants contributed data to each outcome.

The arm descriptions identify five participant groups: normal subjects, healthy smokers, mild-moderate asthma, severe asthma, and COPD classified as Gold Stage I–III. The asthma groups are described as subgroups distinguished using GINA guidelines. The COPD group is described as classified by severity of airflow limitation using GOLD guidance. The registry also lists interstitial lung disease, cystic fibrosis, and patients requiring lung transplant as conditions, but does not report how those conditions correspond to the five arm descriptions or whether they contributed to a particular analysis.

The record does not describe a randomized treatment allocation. It explicitly cautions that the arms are not a like-for-like control comparison, and allocation is not stated. Accordingly, these groups should be read as participant categories rather than treatment and control arms. Differences between categories could reflect participant characteristics or disease status, as well as the physiological features under study; a causal treatment effect is not the question established by this design.

The rationale describes IOS, MBNW, and exhaled NO measurements as approaches to studying lung physiology. The primary outcome is FEV1, expressed as a mean with standard deviation and associated with a 120-minute timeframe. Secondary outcomes are listed as Calv, AX, R5 EX, J'aw, Sacin, and Scond. The registry does not report detailed visit procedures, the timing of all secondary measurements, eligibility criteria, recruitment methods, or the analysis population for each outcome.

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 FEV1, measured over 120 minutes.

FEV1 is the volume of air forcibly exhaled during the first second of a breathing maneuver. It is a measure of expiratory airflow and is commonly used in lung-function assessment. In this study, the registry identifies FEV1 as the primary outcome, with results intended to be expressed as a mean and standard deviation in liters. The recorded timeframe is 120 minutes.

In general, a mean describes the average measurement in a group, while a standard deviation describes how spread out individual measurements are around that average. These summaries can characterize lung function within a participant group, but they do not by themselves establish whether groups differ meaningfully or explain why any difference exists. Interpretation of group differences would require the actual estimates, their uncertainty, and information about the analysis and participant populations.

The registry record does not report FEV1 means, standard deviations, group-specific results, an estimated contrast, a confidence interval, or a p-value. The population attached to the primary outcome is also not specified in the record. Therefore, the endpoint definition is available, but the posted results do not establish the observed FEV1 values or the precision of any comparison.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a mean and standard deviation convey?

The primary outcome is a continuous measurement summarized as a mean and standard deviation. In general, a mean gives a central summary of measured values, and a standard deviation describes their spread. These summaries are useful for describing a group, but are not a complete comparison. A difference between group means, if estimated, would need an uncertainty measure and a clearly stated comparison to show how precisely the data distinguish among possible values. The registry record reports the intended summary format but not the actual means, standard deviations, or estimated differences.

What does a confidence interval add?

In general, a confidence interval expresses uncertainty around an estimate under the method used to calculate it. Narrower intervals indicate greater precision, while wider intervals indicate less precision. An interval also helps distinguish the estimated effect from the range of effects that remain compatible with the data. No confidence interval for FEV1 or another outcome is reported in the registry record. Without an estimate and interval, the precision of any group comparison cannot be evaluated.

Why does the group structure matter?

These are participant groups, not randomized treatment assignments. The record identifies healthy and disease groups, but explicitly says the arms are not a like-for-like control comparison. In general, an observational comparison can be influenced by differences between groups in characteristics other than the one of interest. Randomization is not described, and allocation is not stated. The registry does not report an adjusted analysis that might address measured differences between groups. Any comparison, if results were available, would therefore need to be interpreted as an association unless stronger design and analysis information supported another interpretation.

Why can sample size affect precision?

In general, estimates based on more observations tend to be more precise when other aspects of the data are similar. Precision also depends on variability and the analysis method. The registry reports an enrollment of 126, but does not report outcome-specific numbers analyzed. The group-specific numbers at risk in the safety listing do not establish how many participants had FEV1 or secondary-outcome measurements. The record does not report a sample-size justification or an outcome-specific precision assessment.

A planning illustration based on an observed effect is not the same as a design-stage justification, and a calculated sample size is not observed power. General planning calculations depend on assumptions about the target effect, significance level, allocation, and statistical approximation. The record describes an illustrative approach using a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and effects defined as fractions of an observed effect. It also says that time-to-event calculations use total events, whereas other calculations use participants per arm. These are planning assumptions, not evidence that the study was designed or analyzed in that way. The registry does not report the trial’s own sample-size justification, and the outcome results needed to evaluate an observed-effect illustration are not reported in the registry record.

What does over-dispersion mean in general?

Over-dispersion is a general issue in some count-data models: observed variability exceeds what a simpler model assumes. If ignored, uncertainty can be understated and statistical tests may be too optimistic. It is not possible to determine whether over-dispersion is relevant to the listed outcomes from the registry record. The primary outcome is continuous, and the record does not describe models or diagnostics for any analysis.

What can be inferred from the analysis record?

The registry lists no analyses and reports no estimates, confidence intervals, or p-values for the outcomes. It does not describe a statistical analysis plan, adjustment variables, model forms, hypothesis tests, interim analyses, or handling of repeated or correlated measurements. Those details are not reported in the registry record. General statistical principles can explain what such methods would do, but cannot establish which methods were used in this study.

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("Mild-moderate Asthma", "Severe Asthma", "Normal Subjects", "Healthy Smokers", "COPD (Gold Stage I-III)")
n   <- c(20, 23, 29, 20, 34)
m   <- c(3.03, 2.32, 3.18, 2.76, 1.67)
sp  <- c(0.8, 0.88, 0.79, 0.73, 0.44)
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  Mild-moderate Asthma  20  3.030  0.800  2.656  3.404
CARM  Severe Asthma  23  2.320  0.880  1.939  2.701
CARM  Normal Subjects  29  3.180  0.790  2.880  3.480
CARM  Healthy Smokers  20  2.760  0.730  2.418  3.102
CARM  COPD (Gold Stage I-III)  34  1.670  0.440  1.516  1.824

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome, FEV1, and six secondary outcomes: Calv, AX, R5 EX, J'aw, Sacin, and Scond. Considering several outcomes or multiple group comparisons can raise a multiplicity issue. In general, the more hypotheses examined, the greater the chance that at least one result appears statistically notable by chance if no adjustment or other prespecified strategy is used. The registry does not report how multiplicity was handled, whether outcomes were tested inferentially, or which comparisons were planned.

The record does not report a statistical analysis plan, an analysis population, or rules for excluding measurements. It also does not describe missing-data methods, imputation, or how incomplete tests were handled. These details are not reported in the registry record; it would be inappropriate to assume that all enrolled participants contributed to every outcome or that missing observations were handled in a particular way.

Enrollment was 126, but outcome-specific denominators are not reported. The safety group counts describe participants at risk for adverse-event reporting and do not establish the number contributing to each physiological analysis. No information is reported about withdrawals, unusable measurements, or the reasons for missing outcome data. Without those details, readers cannot assess whether available measurements might differ systematically from missing ones or how that could affect the estimates.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The registry’s safety listing reports zero serious adverse events and zero other adverse events for each of the five described groups. The numbers at risk are 20 for mild-moderate asthma, 23 for severe asthma, 29 for normal subjects, 20 for healthy smokers, and 34 for COPD (Gold Stage I–III). These entries are counts within the safety listing; they should not be assumed to equal the number analyzed for every physiological outcome.

Deaths are recorded as null for each group, which means death counts are not reported in the registry record. The record also gives no serious adverse-event terms. A reported zero is a registry count, not proof that an event was impossible or that every participant was observed for the same period. The safety data do not provide event definitions, collection procedures, follow-up completeness, or detail about attribution to a study procedure.

These counts describe reporting in this record and are not a comparison of treatment safety: the study is not described as a randomized treatment comparison. They also do not establish the safety profile of a treatment or procedure. The posted safety information should be read narrowly as the event counts and denominators recorded for the listed groups.

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

The registry identifies a scientific question about whether measurements such as IOS and MBNW can characterize small-airway physiology across healthy and diseased states, and whether exhaled NO measurements relate to airway inflammation and small-airway disease. It also identifies FEV1 as the primary outcome and lists several secondary physiological measures. These descriptions explain the study’s intended focus, but they are not results.

The registry record does not report numerical results for FEV1 or the secondary outcomes. It therefore does not show whether the groups differed, the size or direction of any difference, or how precisely a difference was estimated. Nor does it report statistical tests or adjusted analyses. The study’s completed status and enrollment count cannot substitute for those missing outcome results.

Even when results from group comparisons are available, this design requires cautious interpretation. The record does not describe randomized allocation and explicitly states that the arms are not a like-for-like control comparison. Differences between groups would describe associations in the enrolled participant categories; they would not by themselves establish that a disease caused a physiological pattern or that a particular measurement predicts a clinical outcome.

The safety listing records zero serious and zero other adverse events in the groups, with deaths not reported. Those entries are limited to the safety information recorded and do not establish that no events occurred outside the record’s reporting scope. No treatment-effect conclusion or clinical recommendation follows from these data.

14. Why This Trial Matters Statistically

This study is statistically interesting because it brings together several physiological measurement approaches with distinct intended roles. The rationale describes spirometry as useful for lung-disease assessment but not informative about peripheral-airway resistance, while IOS is described as potentially capturing airway resistance and elastic properties. MBNW is described as a way to derive ventilation and small-airway indices, and exhaled NO at multiple flow rates as a way to investigate inflammation in different parts of the respiratory system. Comparing these measures across defined participant categories could help characterize how measurements relate to disease groups.

The group structure also illustrates why a careful distinction between descriptive and causal questions matters. Healthy participants, healthy smokers, asthma subgroups, and participants with COPD are not randomized arms, and the record warns that they are not like-for-like controls. Statistical comparisons among such groups may describe patterns, but interpretation depends on who was measured, how groups differ, and whether analyses account for relevant characteristics. The registry does not report those analyses.

The record is also a useful example of the difference between a study’s scientific rationale and its posted evidence. It names the primary and secondary outcomes and records enrollment and completion, but does not include outcome estimates or their uncertainty. Without those results, readers cannot assess whether the proposed measures distinguished groups or whether estimated relationships were precise. The statistical value of the study’s question is clear from its measurement focus; the registry results available do not establish an answer.

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 interpreting the posted evidence is that numerical outcome results are not reported in the registry record. Although FEV1 is identified as the primary outcome and secondary outcomes are listed, no group summaries, contrasts, confidence intervals, or p-values are reported. This prevents assessment of the direction, magnitude, and precision of the findings.

The registry’s condition list includes interstitial lung disease, cystic fibrosis, and patients requiring lung transplant, while its arm descriptions identify five groups: normal subjects, healthy smokers, mild-moderate asthma, severe asthma, and COPD. The relationship between the additional conditions and the described groups is not reported in the registry record. The primary outcome population is also unspecified.

Outcome-specific sample sizes, missing-data handling, eligibility details, measurement procedures, statistical models, adjustment variables, and multiplicity methods are not reported in the registry record. The enrollment count does not establish the number with complete measurements. The safety denominators cannot be used to fill that gap because they refer to safety reporting.

The registry does not state allocation, and it cautions that the groups are not a like-for-like control comparison. This limits causal interpretation of any group differences. The record also does not report a sample-size justification, interim analyses, or a detailed statistical plan. Those omissions leave important design and analysis uncertainties, independently of the absence of posted outcome estimates.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: The Natural History of Small Airways Physiology in Diseased and Healthy States — NCT00677560.
• Registry record last updated 2021-12-20; status last verified 2021-11.
• Results first posted 2021-12-20.
• 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

NCT00677560 is recorded as a completed study sponsored by Imperial College London, with enrollment of 126. The recorded start date is 2010-06-22 and primary completion date is 2013-07-10. The described groups include healthy subjects, healthy smokers, asthma subgroups, and COPD participants. The registry also lists interstitial lung disease, cystic fibrosis, and patients requiring lung transplant among the conditions.

FEV1 is the primary outcome, expressed as a mean and standard deviation in liters, with a timeframe of 120 minutes. Listed secondary outcomes are Calv, AX, R5 EX, J'aw, Sacin, and Scond. The safety listing records zero serious and zero other adverse events in each described group; deaths are not reported.

The record does not report outcome estimates or statistical analyses. It identifies the groups as nonrandomized and not like-for-like controls, so any group comparisons would need cautious, noncausal interpretation.