School-based Asthma Therapy: Stage 2 Effectiveness Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for School-based Asthma Therapy: Stage 2 Effectiveness Study (NCT01175369), a randomized na study. The primary outcome is Number of Symptom Free Days.

2. Clinical Question

The study was designed to assess whether a comprehensive school-based program could reduce asthma-related morbidity. The primary outcome addressed that question through reported symptom-free days, rather than through a measure of medication use or a clinical event count. The comparison concerns the groups as listed in the registry record; the result does not isolate the effects of medication administration from the home tobacco-smoke reduction component.

The record also describes a secondary hypothesis focused on smoke-exposed children: whether those receiving the school-based program with tobacco-smoke reduction would experience less asthma morbidity than those receiving usual care. However, subgroup-specific results are not reported in the registry record. The posted primary comparison therefore answers a broader question about the overall study groups, not the separate question for smoke-exposed children.

3. Trial Design

This was a randomized, parallel-group study of School-based Care and Usual Care. The registry lists the masking as single, but which people were masked is not reported in the registry record. The study is marked as completed and has phase listed as not applicable.

The intervention was behavioral and included directly observed administration of preventive asthma medication in school, with dose adjustments according to National Heart, Lung, and Blood Institute guidelines, plus a home-based environmental tobacco smoke reduction program for children living with one or more smokers. Usual Care was described only as usual asthma care. The record does not specify further details of the comparator or describe how adherence to either group’s care was assessed.

Enrollment is listed as 530. The primary-outcome results report 263 children in the Usual Care group and 260 in the School-based Care group. These are the group counts attached to the posted outcome, and they should be read in that context rather than treated as a description of every analysis population. The record does not explain the relationship between the enrollment figure and the primary-outcome group counts.

The study began in 2006-08, with primary completion in 2009-06. Asthma is the listed condition. The University of Rochester is listed as sponsor. The registry record does not report the original design assumptions, including the sample-size justification, the intended detectable effect, or whether interim analyses were planned. It also does not provide detailed information about concealment of allocation, recruitment, eligibility criteria, or the identities of those masked.

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 Symptom Free Days, measured over Average Symptom Free Days, over 2 weeks, during peak asthma season (November-February).

The primary endpoint was the number of symptom-free days, reported as a mean in days. It represents the average number of days without asthma symptoms during a 2-week period assessed in peak asthma season. The record describes data collection during November, December, January, and February during the school year, and names the timeframe as average symptom-free days over 2 weeks during peak asthma season (November-February).

A symptom-free-day measure is used to summarize asthma-related symptoms over a defined observation period. In general, a mean can make a group-level comparison of a continuous outcome, while the standard deviation describes how much individual observations vary around the group mean. This endpoint provides a summary of symptom experience; it is not itself a count of severe events, a measure of lung function, or a direct measure of medication adherence.

The posted results give a mean of 10.7 days for Usual Care and 11.6 days for School-based Care, with standard deviations of 3.1 and 2.5 days, respectively. The registry does not report a more detailed scoring definition for what counted as symptom-free, how the 2-week observation period was selected for each child, or how repeated seasonal observations, if any, contributed to the reported mean.

7. Results Posted in the Registry

• School-based Care: mean 11.60 versus 10.70 on control; difference 0.90 (95% CI 0.42 to 1.38), standardized effect d = 0.32; z-test p = <0.001.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary endpoint is continuous: the number of symptom-free days is summarized with a mean and standard deviation. The registry labels the parameter as a mean and the measure of dispersion as a standard deviation. The group means describe the average outcome in each arm; the standard deviations describe variability among observations within each arm. Neither measure gives the full shape of the outcome distribution.

What does the mean difference represent?

The comparison is reported as a mean difference of 0.9 days, with School-based Care as the comparison arm against Usual Care. A mean difference is the contrast between the two group averages in the units of the outcome, so the result remains interpretable in days. The posted means are 11.6 days for School-based Care and 10.7 days for Usual Care. This summary does not describe individual-level changes, and the record does not state that the comparison is a change from baseline.

What does the p-value tell the reader?

The unadjusted p-value is <0.001. In general, a p-value describes how incompatible the observed data are with a specified null hypothesis under the statistical assumptions used for the test. A small p-value is not an estimate of the probability that the null is true, and it does not measure the size of the effect. The label unadjusted matters: the record does not report adjustment of this p-value for other outcomes, subgroup comparisons, or covariates.

Why are confidence intervals useful?

In general, a confidence interval presents a range of effect estimates compatible with the data under a specified procedure. It conveys uncertainty around an estimate in a way that a point estimate alone cannot. The registry reports a confidence interval for the mean difference; the precision and interpretation of that interval are discussed separately. A confidence interval does not account for every possible source of uncertainty, such as missing data, outcome measurement, or limitations in the analysis description.

What does randomization contribute?

Random allocation is intended to create groups that are comparable on average before treatment assignment, including for characteristics that may not be measured. That is a general rationale, not proof that every factor was balanced in this particular study. The registry identifies the allocation as randomized but does not report the allocation-generation or concealment procedures, baseline characteristics, or a formal balance assessment. The record also labels masking as single without identifying who was masked.

What does the standard deviation add?

Standard deviations of 3.1 days for Usual Care and 2.5 days for School-based Care provide information about within-group spread. In general, a standard deviation is not the same as the uncertainty in a group mean or in a between-group difference. Those uncertainties also depend on the amount of outcome information and the analysis method. The registry separately reports standard errors for the group means, but does not describe the precise model or computation behind the posted comparison.

What is not described about the analysis?

The registry reports no analysis entries and does not describe the statistical model used for the primary comparison, any adjustment variables, the handling of missing observations, or the analysis population. It also does not report whether there were interim analyses or how the primary endpoint was selected relative to other outcomes. Those elements are not reported in the registry record, so they should not be inferred from the p-value or group summaries. The posted result can be interpreted as a reported unadjusted comparison, but the underlying analytic details cannot be reconstructed from the registry record alone.

For continuous outcomes, the usual interpretation of a mean-based comparison relies on assumptions about the observations and the method used to calculate uncertainty. General concerns can include whether observations are independent and whether the analysis adequately represents the outcome distribution. The record does not report diagnostics or sensitivity analyses for these issues. No claim about a specific assumption violation is warranted from the posted summaries.

10. Confidence Intervals and Precision

The registry reports a mean difference of 0.9 symptom-free days and a confidence interval for that difference. A confidence interval expresses uncertainty around an estimate: in general, it gives a range of values compatible with the data under the procedure used to construct it. The interval is more informative about precision than the point estimate alone, while still depending on the statistical method and assumptions.

The reported interval lies above zero, consistent with the direction of the posted estimate, and its endpoints are relatively close to the estimate in the units of days. This indicates that the reported comparison is more precise than a result with a much wider interval, while not eliminating uncertainty about the true group difference. The interval concerns the mean difference; it is not a range containing the outcomes of most individual children.

The registry record does not describe the interval-construction method, whether it reflects any adjustment, or whether its coverage accounts for multiple outcomes. Its precision should therefore be interpreted for the posted comparison, rather than as a complete statement of uncertainty across all possible analyses. The confidence interval also does not resolve uncertainties that are not represented in its calculation, including the handling of missing outcome data and the absence of a detailed analysis description.

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 planning figures are participants per arm, not total events. They are illustrations based on the observed effect, not the trial’s original design assumptions. The stated calculation uses a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is a stated fraction of the observed effect. The trial’s own sample-size assumptions are not reported in the registry record.

For planning around 100% of the observed effect, the illustration gives 154 participants per arm for 80% power and 206 participants per arm for 90% power. For 75% of the observed effect, it gives 274 participants per arm for 80% power and 367 participants per arm for 90% power. For 50% of the observed effect, it gives 616 participants per arm for 80% power and 824 participants per arm for 90% power.

In general, power is the chance that a planned study will detect an effect of a specified size under its assumptions if that effect is present. The 80% and 90% columns show the planned group sizes associated with those respective power targets for each assumed effect size. Smaller effects require more participants to detect with the same power target. These figures are planning illustrations and are not observed power.

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, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = 0.900; pooled standard deviation σ = 2.818.
2. n = 2 × (1.96 + 0.842)² × 2.818² / 0.900² = 153.9, rounded up to 154 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
delta <- 0.9                      # observed difference in means
sigma <- 2.81774266114111                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^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 (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(1175369)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 154 (80% power), 206 (90% power)
 75% of observed effect: n per arm = 274 (80% power), 367 (90% power)
 50% of observed effect: n per arm = 616 (80% power), 824 (90% power)
power.t.test: 154.8 
Simulated power at n = 154 per arm: 0.795 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-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 one primary outcome, Number of Symptom Free Days, and three secondary outcome categories: Cotinine Level, Cost Effectiveness of the Intervention, and Additional Asthma Morbidity Outcomes. It reports four outcome measures overall, but does not provide the detailed results for all outcome measures in this record. The primary comparison is labeled unadjusted, and the record reports no analysis entries.

When several outcomes or subgroup comparisons are examined, the chance of at least one nominally small p-value can increase. In general, multiplicity procedures can help control that risk, but the choice depends on which comparisons were planned and how they relate. The registry record does not report a multiplicity strategy, a hierarchy among secondary outcomes, or whether the primary result was adjusted for other tests. The unadjusted p-value should therefore be understood as the reported result for this comparison, not as evidence that multiplicity was addressed.

The record describes a secondary hypothesis for smoke-exposed children, but subgroup-specific outcome estimates and analyses are not reported in the registry record. It is not possible to determine from the record whether that subgroup analysis was prespecified, how it was conducted, or whether any interaction between exposure status and study group was assessed.

Missing-data handling is also not reported in the registry record. The record does not state how many primary-outcome observations were missing, why any were missing, whether imputation was used, or whether sensitivity analyses were performed. The analysis population is not specified, so it is not possible to establish whether the posted summary reflects all randomized participants, participants with observed outcomes, or another defined population. These omissions limit evaluation of how missing data or analysis-population choices may affect the result.

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 record lists 265 participants at risk for serious adverse events in Usual Care and 265 in School-based Care. It reports zero serious adverse events in each group. It also lists 265 participants at risk for other adverse events in each group and reports zero other adverse events in each group. Death counts are not reported in the registry record.

These are the posted counts for the adverse-event categories and denominators recorded in the registry. A reported count of zero means that no events were recorded in that category in the posted results; it does not establish that no unrecorded events occurred or that the intervention has no risks. The record does not provide event definitions, collection procedures, severity details beyond the serious-event category, exposure time, or further safety analysis. The adverse-event group counts should not be assumed to match the primary-outcome analysis population.

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

The posted result shows a higher average number of symptom-free days for School-based Care than for Usual Care during the specified 2-week peak-season assessment. The mean difference is 0.9 days, and the unadjusted p-value is <0.001. The reported confidence interval lies above zero, though the registry’s analysis details and interval method are not reported.

This is a comparison of group averages for a combined school-based program. It does not establish that each child experienced more symptom-free days, and it does not identify whether the medication component, the home tobacco-smoke reduction component, or both contributed to the group difference. It also does not provide a separate answer for the smoke-exposed subgroup described in the study’s secondary hypothesis.

The result does not by itself establish the clinical importance of the difference. The registry record does not report a threshold for a meaningful change in symptom-free days. Nor does the posted primary outcome describe other possible aspects of asthma morbidity, such as acute events, or establish effects on outcomes not reported in detail. The secondary outcome categories are listed, but their full results are not available in the registry record.

The record identifies the study as randomized, which is relevant to interpreting a treatment-group comparison, but details about allocation procedures, masking, missing data, and analysis populations are absent. These gaps do not change the values reported, but they constrain how fully the estimate can be evaluated. The findings should be understood as the registry-reported mean comparison for this study, outcome, and timeframe—not as a complete account of all outcomes or of the intervention’s effects in other settings or populations.

16. Why This Trial Matters Statistically

This trial is statistically notable for its combination of a randomized comparison, a continuous symptom-based primary outcome, and a multi-component school-based intervention. The primary result is reported in the outcome’s natural units, symptom-free days, which makes the group contrast directly interpretable as a difference in average days during the stated observation period.

The result also illustrates why a point estimate, uncertainty, and analysis context should be read together. The posted mean difference is 0.9 days, the unadjusted p-value is <0.001, and a confidence interval is reported. Each answers a different question: the estimate describes the observed contrast, the p-value describes evidence relative to a null comparison under the analysis, and the interval conveys uncertainty around the estimate. None alone establishes clinical importance.

The program’s components create an important attribution issue. A group-level contrast can address the combined intervention, but it cannot separate the contribution of school-administered medication from home tobacco-smoke reduction. The record’s subgroup hypothesis adds a question about smoke exposure, yet the corresponding subgroup results are not reported. This highlights the difference between a stated research hypothesis and an available analysis result.

Finally, the registry record leaves key statistical details unreported, including handling of missing outcomes, the analysis population, and multiplicity procedures. These details matter when judging the robustness and scope of a result. The reported comparison remains interpretable as a registry summary, but it does not replace a fuller account of the methods and results across the study’s outcomes.

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 gives limited detail about who was eligible, how participants were recruited, and which population contributed to the primary-outcome analysis. It does not define the analysis population or explain the relationship between the overall enrollment figure and the group counts attached to the outcome. As a result, the reach of the primary estimate cannot be fully assessed from the registry record alone.

Details of randomization and masking are sparse. Allocation is described as randomized and masking as single, but the method of sequence generation, concealment, and the identity of the masked party are not reported in the registry record. Baseline characteristics and their balance between groups are also not included in the registry record recorded for the result.

The primary outcome is described as the average number of symptom-free days over 2 weeks during peak asthma season, but the registry does not give the detailed measurement instrument or the operational definition of a symptom-free day. The record also does not explain how the observation period was chosen for each participant or how any repeated assessments were handled in the reported summary.

Missing-data methods, model specification, covariate adjustment, and sensitivity analyses are not reported in the registry record. The record also does not report detailed outcome results for the three secondary categories or the subgroup focused on smoke-exposed children. These limitations restrict assessment of the full evidence base within the study; they do not permit assumptions about what those unreported analyses would show.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: School-based Asthma Therapy: Stage 2 Effectiveness Study — NCT01175369.
• Registry record last updated 2014-08-01; status last verified 2013-08.
• Results first posted 2013-02-15.
• 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

NCT01175369 is a completed randomized, parallel-group study of School-based Care versus Usual Care for children with asthma. The intervention combined school-based preventive medication administration with a home environmental tobacco smoke reduction program for children living with smokers. The primary endpoint was average symptom-free days over 2 weeks during peak asthma season.

The posted means were 10.7 days for Usual Care and 11.6 days for School-based Care. The registry reports a mean difference of 0.9 days and an unadjusted p-value of <0.001. The record lists three secondary outcome categories, but their detailed results and the smoke-exposed subgroup results are not reported in the registry record. Important details about the statistical analysis and missing data are also not reported.