Progression of Airway Obstruction in Childhood Asthma: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Progression of Airway Obstruction in Childhood Asthma (NCT00873873), a registered phase not stated study. The primary outcome is Airway Wall Thickness.

2. Clinical Question

The study concerns children with asthma and patterns of pulmonary function over time. Its description focuses on whether airway inflammation indicators are associated with structural and physiologic changes in the lung, and on gaining insight into asthma progression in adolescence and early adulthood. The primary registered measure is airway wall thickness, assessed by chest CT at Year 2.

3. Trial Design

The record is for the completed study “Progression of Airway Obstruction in Childhood Asthma,” sponsored by National Jewish Health. It lists a start date of 2008-09, primary completion in 2011-06, and enrollment of 55. The study description places the investigation in the context of a 10-year observation period during the NHLBI Childhood Asthma Management Program, where distinct patterns of pulmonary function loss were identified in children with mild to moderate asthma. The registry dates do not specify each participant’s observation schedule.

The four listed groups are Persistent Obstruction, Late Obstruction in Pulmonary Physiology, Late Normal in Pulmonary Physiology, and Persistent Normal in Pulmonary Physiology. The arm descriptions identify these as patterns of asthma progression. The record does not describe assigned treatment arms, randomization, or allocation; it explicitly cautions that the groups are not a like-for-like control comparison. Their labels are best understood as classifications of pulmonary physiology, not as evidence of an intervention.

The primary outcome is airway wall thickness, a continuous measure summarized as a mean with standard deviation. It is described as segmental average airway wall thickness in mm, measured at Year 2. The record states that 43 participants had chest CT data and that 1 was excluded from the analysis because of an incidental anatomical congenital anomaly. It does not state the number included in the final analysis or the rules used to define the four patterns.

A secondary outcome is listed as Protease/Antiprotease. The record identifies 2 outcome measures and 1 analysis, but does not explain the analysis method or its relationship to the outcome measures. The study is marked COMPLETED. The primary outcome’s group summaries and inferential results are 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.

Before assignment: Analysis of serial pulmonary function measures in participants in CAMP and CAMPCS over time showed 4 patterns of airway obstruction developing during childhood and adolescence based on measurements of pre-bronchodilator FEV1/FVC at the time of enrollment in CAMP and again at the end of the observational phase.

Overall Study

Analysis population for the primary outcome, as defined in the registry: There were 43 participants with Chest CT data; 1 was excluded from the analysis due to incidental finding of an anatomical congenital anomaly.

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 Airway Wall Thickness, measured over Measured at Year 2.

Airway wall thickness is a structural measure of the airway. The registered endpoint is the segmental average airway wall thickness, recorded in mm and measured by chest CT at Year 2. The registry specifies a mean and standard deviation as the summary form. A mean describes the central value of a continuous measurement; the standard deviation describes how dispersed individual measurements are around that mean.

In general, airway structure is relevant to research on asthma progression because structural and physiologic changes in the lung may be associated with ongoing airway inflammation. The study description says it measures indicators of airway inflammation associated with structural and physiologic changes, to provide insight into mechanisms of progression in adolescence and early adulthood. Airway wall thickness supplies a structural measure for that research question; it is not itself a direct measure of inflammation.

The endpoint could be compared across the pulmonary physiology patterns, but the registry record does not report the group means, standard deviations, estimated differences, confidence intervals, or test results. It also does not describe the CT acquisition or measurement procedures beyond the segmental average measure and Year 2 timing. Without those results and details, the endpoint’s observed magnitude and precision cannot be assessed from the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies a continuous primary outcome summarized as a mean with standard deviation. It does not report the inferential method used for that outcome. The explanations below describe general statistical concepts and should not be read as a description of an undocumented analysis.

What does a mean describe?

For a continuous measure such as airway wall thickness, the mean is the arithmetic average of the observations included in a group summary. It provides a compact description of the group’s central measurement, but does not show the full distribution. A mean can be influenced by unusually high or low observations, and two groups with the same mean can still have different distributions.

The standard deviation describes the spread of observed measurements around the mean. It is a measure of variability among observations, not the precision of the estimated mean. Precision also depends on the amount of information available and the analysis assumptions. A standard deviation should not be interpreted as a confidence interval or as a measure of treatment effect.

How would a group comparison be interpreted?

In general, a comparison of means estimates how far apart the group averages are. The estimate’s direction indicates which group has the higher average under the chosen contrast, while its magnitude describes the scale of the difference in the outcome’s units. A confidence interval gives information about uncertainty in that estimate. The registry record reports neither group averages nor an estimated contrast or confidence interval for airway wall thickness, so these features cannot be interpreted for this study from the record.

Statistical significance and clinical relevance are separate questions. A test result concerns compatibility with a null hypothesis under a specified model; it does not show whether an estimated difference is large enough to matter in a clinical or biological context. Assessment of relevance also requires subject-matter context and a clear estimate with uncertainty. No test result or clinical threshold for airway wall thickness is reported in the registry record.

Why does study design matter?

Random assignment, when used, can help balance factors that influence outcomes between assigned groups. Here, the registry says the comparison is not randomized and allocation is not stated. The groups are named for pulmonary physiology patterns. As a general matter, group differences in an observational setting can reflect the patterns themselves, other participant characteristics, or selection into the groups and into the available measurement data. A statistical adjustment can address measured factors under its assumptions, but cannot automatically remove bias from unmeasured factors. The registry record does not report whether adjustment was used.

The CT endpoint has a stated availability and an exclusion due to an incidental anatomical congenital anomaly. In general, missing measurements can affect an estimate if the participants with measurements differ systematically from those without them. Excluding a participant can also affect the analysis population and its interpretation. The registry record does not describe missing-data handling, the final analysis population, or whether any sensitivity analysis was conducted.

What do the planning illustrations mean?

Sample-size planning uses assumptions about the target effect, variability, allocation, significance level, and analysis method to estimate how much information a future study might need. The registry’s planning assumptions describe a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The planning illustration is based on the observed effect, with the effect to detect expressed as a stated fraction of that observed effect.

These calculations are planning illustrations, not the study’s own design justification. The registry record does not report a sample-size justification for the study, and the groups are not randomized treatment arms. A planning calculation based on an observed effect is also sensitive to uncertainty in that observed effect. It should not be interpreted as observed power or as evidence that the study was adequately powered. The relevant planning values are not reported in the registry record.

Why is the analysis method important?

Continuous measurements may be analyzed using different methods depending on their distribution, the comparison being asked, the group structure, and any adjustment variables. The assumptions and target of an analysis differ across methods. For example, a method that compares unadjusted group means answers a different question from a model that adjusts for measured participant characteristics. The record gives the outcome’s summary type but does not report the model, test, assumption checks, covariates, or contrast definition. No particular method should therefore be attributed to the investigators.

The record lists 1 analysis and 2 outcome measures, but that information alone does not establish which endpoint was included in the analysis, how outcomes were handled together, or whether planned and reported analyses were the same. The statistical method and the numerical results would be needed to evaluate those questions. Until those details are reported, interpretation should remain focused on the registered measurement and the limits of the available record.

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("Persistent Obstruction", "Late Obstruction", "Late Normal", "Persistent Normal")
n   <- c(15, 7, 8, 12)
m   <- c(1.5, 1.5, 1.4, 1.6)
sp  <- c(0.2, 0.2, 0.1, 0.3)
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  Persistent Obstruction  15  1.500  0.200  1.389  1.611
CARM  Late Obstruction  7  1.500  0.200  1.315  1.685
CARM  Late Normal  8  1.400  0.100  1.316  1.484
CARM  Persistent Normal  12  1.600  0.300  1.409  1.791

11. Multiplicity, Missing Data and Analysis Populations

The registry identifies 2 outcome measures and 1 analysis. A secondary outcome is named Protease/Antiprotease, alongside the primary airway wall thickness endpoint. The record does not state whether both outcomes were analyzed together, whether additional comparisons were performed, or whether any adjustment was made for multiplicity. Multiplicity concerns arise when several outcomes or contrasts are examined: repeated testing can increase the chance of finding an apparently notable result by chance. Whether and how that issue applies depends on the analysis plan, which is not reported in the registry record.

The record reports that 43 participants had chest CT data and that 1 was excluded from the analysis due to an incidental anatomical congenital anomaly. It does not identify the final analysis population or explain the handling of measurements that were unavailable for other reasons. Missing-data methods, imputation, and sensitivity analyses are not reported in the registry record. In general, an analysis limited to participants with observed measurements can be biased if measurement availability is related to the outcome or to factors associated with it.

It is also not reported whether participants were analyzed according to a prespecified classification, how the four pulmonary physiology patterns were assigned, or whether exclusions were prespecified. The record’s statement that the comparison is not randomized and allocation is not stated underscores that the pattern groups are not intervention arms. Analysis populations and group definitions matter because they determine what comparison an estimate represents. The registry record does not report a statistical analysis plan, a multiplicity strategy, or enough detail to assess departures from any planned analysis.

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 adverse event record lists four pulmonary physiology groups. For Persistent Obstruction, the numbers at risk are 20 for serious events and 20 for other events, with 0 affected in each category. For Late Obstruction in Pulmonary Physiology, the corresponding numbers at risk are 7 and 7, with 0 affected in each category. For Late Normal in Pulmonary Physiology, they are 9 and 9, with 0 affected in each category. For Persistent Normal in Pulmonary Physiology, they are 18 and 18, with 0 affected in each category.

These are registry counts for the listed groups, not evidence that no adverse events could occur. The record does not describe the event collection window, definitions, completeness of reporting, or whether the groups had comparable observation. The group labels reflect physiology patterns, not randomized safety assignments. Death counts are not reported in the registry record. The zero affected counts should be read as the recorded counts, not as proof of absence of risk or as a treatment-safety comparison.

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

The record identifies a research question about asthma progression and a structural lung measure: segmental average airway wall thickness in mm, measured by chest CT at Year 2. It also gives context for the investigation, describing patterns of pulmonary function loss and the study of inflammation indicators associated with structural and physiologic changes. These details establish what the study set out to examine, but do not establish what the endpoint results were.

The primary outcome’s group means, standard deviations, estimates of group differences, confidence intervals, and test results are not reported in the registry record. The secondary Protease/Antiprotease outcome is named, but its numerical findings are not reported either. Thus, the registry record cannot establish whether airway wall thickness differed among the patterns, how large any difference was, or how precisely it was estimated. It also cannot show whether the inflammation indicators were associated with the structural measure.

The group classifications are not randomized treatment assignments. The record explicitly says this is not a randomized comparison and that allocation is not stated. A difference between pattern groups, if numerical results were available, would be an observational association and should not be interpreted as a causal effect of a treatment. The registry record also does not report the adjustment methods or other design details needed to assess potential confounding.

The CT availability statement and the exclusion due to an incidental anatomical congenital anomaly give limited information about the primary outcome population. They do not establish the final analysis count or how unavailable measurements were handled. Those omissions limit assessment of the representativeness and precision of any analysis.

Accordingly, the record supports a description of the study’s aim, groups, primary measurement, and limited safety counts. It does not support a conclusion that a treatment works or does not work, nor does it confirm a mechanism of progression. The numerical endpoint findings and analysis details are not reported in the registry record.

14. Why This Trial Matters Statistically

This study illustrates a common statistical challenge in clinical research: a clearly named endpoint and study question do not, by themselves, make a result interpretable. Airway wall thickness is specified as a continuous measure, with a defined unit, measurement method, and timeframe. Yet without group summaries and an estimate of the comparison, readers cannot assess the direction or magnitude of the outcome or its uncertainty.

It also highlights the distinction between classification groups and randomized arms. The four labels describe pulmonary physiology patterns, and the registry says the comparison is not randomized. This matters because an observed difference across patterns would not automatically indicate that one pattern caused a change in airway structure. The design determines which causal claims can be supported, while analysis details determine how the reported estimate should be understood.

The record also shows why analysis population information is essential. It states that chest CT data were available for 43 participants and that 1 was excluded for an incidental anatomical congenital anomaly, but does not report the final analysis population or other missing-data handling. Those details help readers judge the scope of the findings and possible selection effects.

Finally, the study’s stated focus links airway inflammation indicators with structural and physiologic change, while the primary endpoint is a structural measurement and Protease/Antiprotease is listed as secondary. Reporting the outcome estimates, uncertainty, and analysis methods would be needed to evaluate that proposed relationship. The registry record supplies a useful outline of the question, but not the numerical evidence needed to answer it.

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.

Several trial-specific limitations follow from the registry record. The primary outcome is described, but group-specific airway wall thickness values and inferential results are not reported in the registry record. This prevents assessment of the observed association, its magnitude, and its precision. The record also does not give the statistical model, test, contrast definition, covariates, or assumption checks.

The comparison is not randomized, and allocation is not stated. The groups are defined by pulmonary physiology patterns, but the criteria used to assign those patterns are not reported in the registry record. Group differences, if present, could reflect factors associated with pattern classification as well as differences in airway structure. Adjustment for confounding is not described.

For the primary CT measure, the record states that 43 participants had data and that 1 was excluded because of an incidental anatomical congenital anomaly. The final analysis population, reasons for any other unavailable measurements, and missing-data methods are not reported in the registry record. This limits evaluation of selection and the effect of exclusions.

The study description situates the work within a 10-year observation period during the NHLBI Childhood Asthma Management Program, but the registry does not specify participants’ individual follow-up schedules or the detailed timing of other measurements. It lists Protease/Antiprotease as a secondary outcome without reporting its result. Multiplicity handling, a statistical analysis plan, and a sample-size justification are not reported in the registry record. These omissions limit both reproducibility and interpretation.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Progression of Airway Obstruction in Childhood Asthma — NCT00873873.
• Registry record last updated 2020-10-22; status last verified 2020-10.
• Results first posted 2012-01-06.
• 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

The completed record describes “Progression of Airway Obstruction in Childhood Asthma,” sponsored by National Jewish Health, with enrollment of 55. It lists a start date of 2008-09 and primary completion in 2011-06. The study description concerns pulmonary function patterns in children with mild to moderate asthma and investigation of inflammation indicators associated with lung changes.

The primary outcome is segmental average airway wall thickness in mm, measured by chest CT at Year 2 and summarized as a mean with standard deviation. The record states that 43 participants had CT data and that 1 was excluded due to an incidental anatomical congenital anomaly. Four pattern groups are listed; the registry cautions that the comparison is not randomized and allocation is not stated. Protease/Antiprotease is listed as a secondary outcome. Primary endpoint results, analysis details, and the final analysis population are not reported in the registry record.