Study of the Mechanisms of Asthma: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Study of the Mechanisms of Asthma (NCT00595153), a non-randomized phase 1 study. The primary outcome is Gene Expression in Airway Secretions and Tissues.

2. Clinical Question

3. Trial Design

NCT00595153, titled “Study of the Mechanisms of Asthma,” was a Phase 1, completed study sponsored by the University of California, San Francisco. The registry lists a non-randomized allocation, no masking, and a parallel model. Enrollment was 127. The recorded start was 2007-04 and primary completion was 2011-06.

The record describes three groups rather than a randomized treatment-versus-control allocation. Healthy, non-asthmatic participants were not to receive an intervention. Asthmatics not using inhaled corticosteroids were to start an inhaled steroid during the study. Asthmatics already using inhaled corticosteroids were to receive a standardized dose. Pulmicort is listed as a drug intervention, but the record does not specify its assignment to each group in the arm descriptions.

The primary outcome time points differed by group: healthy controls and steroid-naive asthmatics were assessed at Visit 2, at 1 week, while steroid-treated asthmatics were assessed at Visit 5, at 9 weeks. These differences matter when interpreting comparisons, because group membership and assessment timing were not the same across all groups. The registry record does not report a randomized comparison, masking, or a detailed statistical analysis plan. Its description therefore supports a study of airway gene-expression patterns in these groups, not a causal estimate of an intervention effect.

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: Steroid naïve asthmatics had bronchoscopy before and after an 8 week treatment with inhaled corticosteroids, and asthmatics already taking an inhaled corticosteroid had their treatment standardized for 8 weeks followed by a bronchoscopy. Healthy control subjects participated in a cross-sectional study for characterization and bronchoscopy.

Overall Study

Analysis population for the primary outcome, as defined in the registry: Participants who met inclusion/exclusion requirements and completed all study activities were included in the analysis. Specifically, this included: 1\. Having a bronchoscopy with complete PCR on RNA from epithelial brush samples.

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 Gene Expression in Airway Secretions and Tissues, measured over Healthy Control: Visit 2 (at 1 week); Steroid Naive Asthmatics: Visit 2 (at 1 week); Steroid Treated Asthmatics: Visit 5 (at 9 weeks).

The primary endpoint was the scaled mean value of three IL-13 signature genes in airway secretions and tissues: PERIOSTIN, calcium-activated chloride channel regulator 1 (CLCA1), and plasminogen activator inhibitor-2 (SERPINB2). The record describes measuring relative expression with real-time PCR, using log base-2 transformed values normalized to the geometric mean of five housekeeping genes.

For each gene, the normalized values were centered by subtracting that gene’s mean and scaled by dividing by that gene’s standard deviation. The three resulting values were then averaged for each participant to form the “three-gene-mean” metric. This approach gives each gene an equal, assay-independent contribution to the composite, as described in the record. In general, standardizing component measures in this way places them on a common scale before combining them.

The endpoint is a gene-expression measure, not a direct measure of symptoms, lung function, or clinical benefit. It was used to characterize an airway IL-13-related expression pattern. The registry record does not report the observed mean or standard deviation for any group, or a comparison of the groups on this endpoint.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a continuous primary outcome summarized as a mean with standard deviation. It defines the outcome as a participant-level average of three standardized gene-expression values. The method begins with relative gene-expression measurements for PERIOSTIN, CLCA1, and SERPINB2, obtained using real-time PCR and normalized with the geometric mean of five housekeeping genes. The normalized expression values are log base-2 transformed. Each gene’s values are then centered and scaled before the three values are averaged for each participant.

What does centering and scaling do?

General statistical explanation: centering expresses a measurement relative to the mean for that measure, while scaling expresses it relative to its standard deviation. These operations put component measures on a common standardized scale. Averaging the standardized values makes a composite in which each component contributes equally by construction, as the registry describes. The resulting metric is not a raw expression value for any single gene. Its interpretation depends on the normalization and standardization steps used to create it.

The registry says participants were included in the primary-outcome population if they met the inclusion and exclusion requirements, completed all study activities, and had a bronchoscopy with complete PCR on RNA from epithelial brush samples. It does not report the number included in the analysis by group, how many did not meet these conditions, or whether any values were missing for other reasons. It also does not describe imputation, exclusion rules beyond the stated population description, or sensitivity analyses.

Why do standard deviations and confidence intervals matter?

General statistical explanation: a mean describes the central value of a continuous measure, while a standard deviation describes the spread of participant values around that mean. A confidence interval describes the uncertainty around an estimate under the assumptions of the analysis; it is not a range containing a fixed proportion of individual observations. The registry record reports neither group-specific means and standard deviations nor confidence intervals for the primary endpoint. Therefore, the dispersion of the metric and the precision of any group contrast cannot be evaluated from the posted outcome information.

What can the planning illustration say?

The planning illustration is described as using the observed effect, a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It considers an effect to detect stated as a fraction of the observed effect. For non-time-to-event outcomes, the illustration is expressed as participants per arm. These are planning assumptions, not the trial’s reported design justification and not observed power. The registry record does not report the study’s own sample-size justification or the statistical plan used to choose enrollment. Nor does the planning illustration make the non-randomized groups equivalent to randomly allocated arms.

General statistical explanation: a sample-size calculation asks how many participants a hypothetical design would require under specified assumptions about the effect, variability, allocation, and significance level. A calculation based on an observed effect is a planning illustration, not evidence that the study had a particular probability of detecting an effect. The registry record does not report the numerical effect estimate that would be needed to assess such an illustration independently.

Why does over-dispersion matter?

General statistical explanation: over-dispersion means that variability is greater than a statistical model expects. When that occurs, standard errors based on the lower assumed variability may be too small, making estimates appear more precise than warranted. The posted primary outcome is described as continuous, and no model, variance assessment, or over-dispersion finding is reported in the registry record. There is therefore no basis for saying that over-dispersion was present or that a particular correction was used.

The registry record does not report an analysis method for comparing groups, covariate adjustment, a model specification, or a plan for repeated measurements. The endpoint time points differ across groups, and the record does not explain how that timing was handled analytically. Without those details and without the outcome estimates, statistical significance and precision cannot be reconstructed from the endpoint description alone.

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("Healthy Control", "Steroid Naive Asthmatics", "Asthmatics on ICS Treatment")
n   <- c(19, 24, 21)
m   <- c(-0.66, 0.54, -0.3)
sp  <- c(0.36, 0.87, 0.6)
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  Healthy Control  19  -0.660  0.360  -0.834  -0.486
CARM  Steroid Naive Asthmatics  24  0.540  0.870  0.173  0.907
CARM  Asthmatics on ICS Treatment  21  -0.300  0.600  -0.573  -0.027

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists one primary outcome measure: the scaled mean expression of three IL-13 signature genes. It does not report a multiplicity adjustment or a broader statistical plan describing how multiple outcomes, contrasts, or analyses would be handled. The endpoint combines three genes into one metric, but the record does not state whether gene-specific analyses were also planned or performed. No separate gene-level results are reported.

The primary-outcome population is described as participants who met inclusion and exclusion requirements and completed all study activities, including bronchoscopy with complete PCR on RNA from epithelial brush samples. The number of participants satisfying this definition in each group is not reported in the registry record. The relationship between the enrollment of 127 and the endpoint analysis population is also not reported. The record does not describe the extent or handling of missing endpoint data, reasons for non-completion, or sensitivity analyses addressing missingness.

There are no analysis results reported for the primary endpoint. The record does not provide estimates, uncertainty intervals, p-values, adjusted comparisons, or details of an analysis population beyond the eligibility description. Interim analyses and a sample-size justification are not reported in the registry record. These omissions prevent assessment of the planned multiplicity approach, the impact of missing data, and whether the posted analysis followed a prespecified statistical plan. Absence of these details should not be read as evidence that no such procedures occurred; it means they are not reported in the registry record.

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 5% reporting threshold.

Most frequent non-serious adverse event terms

The registry reports serious adverse events as 0 affected in each group: Healthy Control, Steroid Naive Asthmatics, and Asthmatics on ICS Treatment. The corresponding numbers at risk were 24, 42, and 61. The record lists other adverse events affecting 6 of 24 healthy controls, 5 of 42 steroid-naive asthmatics, and 15 of 61 asthmatics on ICS treatment.

These are counts reported for the listed groups, not a randomized safety comparison. The groups differed by asthma status and corticosteroid use, and allocation was non-randomized. The record does not establish that differences in adverse-event counts were caused by treatment. It also does not provide further event-level detail in the serious adverse-event listing; no serious-event terms are listed. Death counts are not reported in the registry record, so the record should not be interpreted as documenting zero deaths. The listed adverse-event counts describe what was recorded, not a complete assessment of comparative risk.

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

The registry record establishes that this completed study was designed to examine an airway gene-expression metric in healthy controls and groups of asthmatic participants with different inhaled corticosteroid histories. It also describes the laboratory steps used to create a three-gene composite and identifies when the groups were assessed. Those details explain what the endpoint represents and how participants were meant to contribute data.

The record does not report the primary outcome values or an analysis comparing groups. It therefore does not show whether the gene-expression metric was higher, lower, or similar across groups, nor how large or precise any difference might have been. No conclusion about statistical significance can be drawn from the endpoint description alone. A missing result is not evidence of no difference.

The non-randomized design is important to what any observed contrast could mean. Healthy controls and participants with asthma are different populations, and participants with and without prior inhaled corticosteroid use were not randomly assigned to those categories. The assessment time points also differ for the steroid-treated group. Even if numerical group contrasts were available, they would need cautious interpretation and could not automatically be attributed to treatment.

The endpoint is a molecular measure of three IL-13 signature genes, not a clinical outcome such as symptoms or lung function. The registry’s stated goals include understanding asthma mechanisms and the effects of inhaled steroids, but the posted outcome information does not establish a treatment effect or a clinical benefit. The record supports description of the study design and measurement approach, while leaving the direction, magnitude, and uncertainty of the primary result unresolved.

14. Why This Trial Matters Statistically

This study is statistically notable because its primary endpoint is a constructed molecular composite rather than a single directly observed clinical measure. The three-gene-mean metric combines PERIOSTIN, CLCA1, and SERPINB2 after normalization, centering, and scaling. That construction affects interpretation: the endpoint represents the average of standardized gene-expression values, not the expression level of one gene or a direct clinical outcome.

The design also highlights the distinction between describing groups and estimating an intervention effect. The study was non-randomized and unmasked, with healthy controls, steroid-naive asthmatics, and asthmatics already on inhaled corticosteroids. The endpoint timing differed for the steroid-treated group. These features make group contrasts vulnerable to differences related to group membership and timing, not only to an intervention.

Finally, the registry record illustrates why an endpoint definition is not enough to interpret a study statistically. The endpoint population is described, but analyzed sample counts, group summaries, effect estimates, uncertainty, and analysis methods are not reported. Without those results, readers cannot assess the size or precision of any observed pattern. The statistical value of a registry entry depends not only on knowing what was measured, but also on having the results and analysis details needed to interpret 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 limitations are specific to the information reported for this study. Allocation was non-randomized and masking was absent. The three groups differ in asthma status and inhaled corticosteroid use, so they do not form a like-for-like randomized comparison. The registry’s own design description therefore does not support treating group differences as causal estimates of an intervention effect.

The timing of the primary outcome also varies by group. Healthy controls and steroid-naive asthmatics were assessed at Visit 2 (at 1 week), while steroid-treated asthmatics were assessed at Visit 5 (at 9 weeks). The record does not describe an analysis addressing this difference. It does not report whether other group characteristics were considered, or whether covariates were adjusted for.

Although enrollment was 127, the number analyzed for the primary endpoint in each group is not reported. The registry describes a population requiring completion of study activities and complete PCR following bronchoscopy, but does not quantify exclusions or missing measurements. Group-level means, standard deviations, effect estimates, confidence intervals, p-values, and analysis methods are also not reported. The sample-size justification, interim analyses, and missing-data procedures are not reported in the registry record.

The composite endpoint depends on laboratory normalization and standardization, and the registry does not report gene-level results alongside the composite. The record lists Pulmicort as an intervention, but the arm descriptions do not specify its assignment to each group. These limits leave the primary result and its interpretation unresolved.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Study of the Mechanisms of Asthma — NCT00595153.
• Registry record last updated 2014-01-20; status last verified 2013-12.
• Results first posted 2014-01-20.
• 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

NCT00595153 was a completed Phase 1, non-randomized, unmasked, parallel study sponsored by the University of California, San Francisco. Enrollment was 127. The study examined a three-gene airway expression metric in healthy controls, steroid-naive asthmatics, and asthmatics already receiving inhaled corticosteroids.

The primary endpoint combined standardized expression values for PERIOSTIN, CLCA1, and SERPINB2. Assessment timing differed by group. The registry record describes the endpoint and an analysis population requiring completed study activities and complete PCR from epithelial brush samples, but does not report analyzed counts by group or numerical primary-outcome results.

Serious adverse events were reported as 0 affected in each listed group; other adverse events were also reported. The record does not report a primary-outcome analysis, statistical plan, or sample-size justification. It therefore does not establish the direction or precision of differences in the gene-expression measure.