Randomized Prospective Trial of a Mobile Health Application for Asthma Self-Management: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Randomized Prospective Trial of a Mobile Health Application for Asthma Self-Management (NCT02333630), a randomized na study. The primary outcome is Number of Emergency Room Visits Secondary to Asthma Exacerbation.

2. Clinical Question

The clinical question is about a count of asthma-related emergency-room visits over a defined follow-up period, not about whether participants used the app or whether their asthma symptoms changed. The registry also lists asthma exacerbations, hospitalizations, and frequency of mobile-application use as secondary outcomes. The population details needed to determine how broadly the findings might apply are not reported in the registry record. In particular, the current trial’s age range and more detailed eligibility criteria are not reported in the registry record.

3. Trial Design

The registry describes a randomized, parallel-group trial with no masking. Participants were assigned to AsthmaCare or to a control condition offering a link to asthma education videos and information. The app was downloaded at recruitment for participants assigned to the intervention, with access available indefinitely after enrollment. Control participants could access their education link at their discretion. The registry record does not describe the randomization procedure or whether allocation was concealed.

The listed enrollment is 200. The outcome summaries give group sizes of 98 for AsthmaCare and 95 for control. The registry does not explain the relationship between enrollment and the group sizes in the posted outcome data. It also does not describe how follow-up, adherence, or missing outcome information was handled. The primary outcome timeframe is six months after study enrollment and randomization. The registry lists the study as completed, with a start in 2014-11 and primary completion in 2016-11.

The primary endpoint is the number of emergency-room visits secondary to asthma exacerbation. The registry reports the mean and standard deviation for each group. A secondary outcome, hospitalizations, is also posted as a mean and standard deviation over six months. Other listed secondary outcomes are number of asthma exacerbations and frequency of use of the mobile application, but quantitative results for those outcomes are not reported in the registry record.

The registry record does not report the trial’s original sample-size justification, planned statistical methods, analysis populations, or any interim-analysis plan. The unadjusted comparisons discussed in the statistical interpretation are recalculations from the posted group summaries; the registry record lists no reported analyses.

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

Reasons for not completing this period:

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 Emergency Room Visits Secondary to Asthma Exacerbation, measured over 6 months.

The primary endpoint counts emergency-room visits for asthma during the six months following enrollment and randomization. It captures one type of healthcare use associated with asthma exacerbation. Because it is a count over a specified period, a participant’s value can be zero or can reflect more than one visit. The registry summarizes the endpoint as a mean and standard deviation in each randomized group.

A group mean gives the average number of visits across the participants included in that group’s outcome summary. The standard deviation describes how much individual counts vary around that mean. These summaries make it possible to compare average visit counts between the intervention and control groups. They do not describe every participant’s experience, the distribution of counts, or the reasons for any visits.

The endpoint is relevant to the trial’s stated aim of assessing clinical outcomes, but it is not a direct measure of app use or of all aspects of asthma control. A difference in average emergency-room visits would need to be interpreted alongside the precision of the estimate, the trial’s design and analysis limitations, and other outcomes. The registry record does not report a threshold for a clinically important difference or explain why this specific endpoint was selected as primary. It also does not report whether emergency-room visits were verified from records, reported by participants, or collected in another way.

7. Results Posted in the Registry

• AsthmaCare Intervention: mean 0.31 versus 0.33 on control; difference -0.02 (95% CI -0.21 to 0.17), standardized effect d = -0.03; z-test p = 0.837.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Hospitalizations

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • AsthmaCare Intervention: mean 0.14 versus 0.10 on control; difference 0.04 (95% CI -0.06 to 0.14), standardized effect d = 0.11; z-test p = 0.435.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between AsthmaCare Intervention and the control. The interval gives the range of effects that remain compatible with the data.

The posted secondary information does not show a uniform direction across outcomes: the app group’s mean is lower for the primary emergency-room endpoint but higher for the hospitalization outcome. The unadjusted hospitalization comparison is also imprecise, with a confidence interval extending across zero. Read together, these results do not provide a consistent pattern of differences across the two outcomes with quantitative results.

The relationship to the primary result is therefore one of context, not confirmation. Hospitalizations and emergency-room visits are distinct measures of healthcare use, and a pattern in one does not automatically establish a similar pattern in the other. The registry also lists asthma exacerbations and frequency of application use as secondary outcomes, but quantitative results for those outcomes are not reported in the registry record. The secondary information cannot establish whether the app was used frequently or whether exacerbation counts differed.

Unadjusted secondary results carry less weight when several outcomes are examined because the chance of observing an apparently notable result can increase as more comparisons are considered. General statistical practice may address this through prespecified outcome hierarchies or multiplicity adjustments, but whether either was used is not reported in the registry record. The record does not state how the secondary outcomes were prioritized, whether their analyses were planned in advance, or whether any adjustment for multiple testing was made.

Accordingly, the secondary results are best treated as descriptive and exploratory. They can help identify areas for further study, but they do not replace the primary endpoint or resolve its uncertainty. Nor do the available secondary data support a broad conclusion about asthma outcomes overall. The registry’s list of outcomes indicates what was of interest; the absence of quantitative results for some listed outcomes means that their findings cannot be assessed from the registry record.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Number of Asthma Exacerbations
• Hospitalizations
• Frequency of Use of the Mobile Health Application

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is a continuous summary of a count: the number of emergency-room visits is recorded for each participant, then the group results are expressed as means and standard deviations. Calling the analysis a mean comparison does not mean that the underlying individual outcome is measured on a continuous scale; the observed visit count is discrete. A mean can still summarize the average count across participants, but it does not show the shape of the count distribution.

The comparison is an unadjusted difference in means. In general, such a difference subtracts the control-group mean from the intervention-group mean. A negative estimate in this setup means the intervention-group mean is lower in the posted summaries; a positive estimate means it is higher. The primary estimate is -0.02 visits. This is a summary contrast, not a causal conclusion by itself. Randomization supports a comparison of assigned groups, but interpretation also depends on how outcomes were collected, whether all randomized participants were included, and whether the analysis followed the planned approach. Details of those matters are not reported in the registry record.

The reported confidence interval expresses uncertainty around the estimated mean difference. In general, a confidence interval is a range of values compatible with the data and the method used to calculate it. It is not a range that contains a known true effect with certainty, and it does not assign probabilities to individual values within its bounds. For the primary outcome, the recalculated interval extends to both sides of zero, so the observed summaries do not distinguish a positive difference from a negative one with the stated method. The exact method used for the registry’s original analysis is not reported in the registry record; the posted comparison is a simple unadjusted recalculation.

The unadjusted p-value is 0.837. In general, a p-value describes how unusual the observed result, or a result more extreme, would be under a specified null hypothesis and statistical model. It is not the probability that the null hypothesis is true, and it does not measure clinical importance. Its meaning depends on the comparison and assumptions. The registry record does not report a prespecified analysis plan, whether tests were one-sided or two-sided for the outcome analysis, or any covariate-adjusted method. The planning illustration, separately, specifies a two-sided significance level of 0.05; that planning assumption should not be mistaken for a reported trial analysis plan.

Why can visit counts need special attention?

General statistical context: counts often have a distribution that differs from the symmetric, bell-shaped pattern assumed by some simple mean-based methods. Many people may have no events, while a smaller number may have multiple events. In general, over-dispersion means that observed variability is greater than a model expects; if present and ignored, uncertainty estimates and tests can be unreliable. These are general considerations for count outcomes, not claims about the distribution in this trial. The registry record does not provide participant-level counts or distributional diagnostics, so it is not possible to assess whether over-dispersion was present or how it was addressed.

A mean difference remains an interpretable measure of the contrast in average visit counts. Other approaches to count data may model event rates or the probability of different counts, but such approaches require assumptions and may answer a somewhat different question. The registry record does not report a count-regression model or another alternative analysis. No model should be attributed to the investigators on the basis of the posted means and standard deviations alone.

What does randomization contribute?

In general, random assignment is intended to make groups comparable on average at the start of a trial, including with respect to factors that are measured and factors that are not measured. This supports causal interpretation if follow-up and analysis preserve the randomized comparison. The registry identifies the study as randomized, but does not report the sequence-generation or allocation-concealment procedures. It also does not state whether the primary analysis followed intention-to-treat, per-protocol, or another population definition. The lack of masking is reported, but the record does not describe how outcome ascertainment may have been affected.

The displayed arm summaries use 98 participants for AsthmaCare and 95 for control. The record lists enrollment of 200 but does not explain how those outcome group sizes relate to the enrolled participants. Without information on missingness, withdrawals, or exclusions, the effect of incomplete outcome data cannot be assessed. The recalculated mean difference and its uncertainty are based on the posted summaries and should not be treated as a substitute for a prespecified, fully documented trial analysis.

What does a recalculation represent?

A recalculation from posted summary statistics uses the group means, group standard deviations, and group sizes to form an unadjusted comparison. It does not recover individual participant data, permit adjustment for baseline variables, or confirm the investigators’ original statistical procedures. The registry record reports no analyses, and the comparison should be understood in that context. The discrepancy indicator is false, so there is no flagged disagreement between the posted summary-based result and a sponsor analysis to resolve.

Overall, the methods support a cautious reading: the arm means are close, the estimated difference is small in the units of the endpoint, and the uncertainty interval includes both directions. The available information does not show whether the analysis assumptions were checked, whether an adjusted analysis was conducted, or how the investigators handled missing data and multiple outcomes.

11. Confidence Intervals and Precision

The primary mean difference is -0.02 visits, with a recalculated confidence interval that extends below and above zero. This interval is central to the precision assessment: it indicates that the estimate is uncertain about both the direction and the size of the contrast. The posted result is therefore not a precise demonstration of a lower or higher average number of visits in either group.

The interval is not evidence that all values within it are equally plausible, nor does it imply that the true effect is likely to be exactly zero. Rather, the data and calculation do not exclude a range of effects on either side of zero. The registry record does not report a threshold for a clinically important difference, so statistical uncertainty cannot be translated into a judgment about whether any possible difference would matter in practice.

The group standard deviations, 0.6 for AsthmaCare and 0.74 for control, show that individual visit counts vary around the group means. The group sizes in the outcome summaries are 98 and 95. Precision depends on both the amount of variation and the amount of information available, as well as the analysis method. The confidence interval is based on a simple unadjusted recalculation and may not capture uncertainty associated with unreported design or analysis choices.

The unadjusted p-value of 0.837 is consistent with substantial uncertainty about whether the observed contrast differs from zero under the recalculation’s assumptions. It should not be read as proof of equivalence or as a measure of the probability that the observed estimate is correct. More complete reporting of the analysis plan, outcome completeness, and participant-level distribution would help readers assess the precision and robustness of the result.

12. 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 and are not the original trial’s design calculations. The stated assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each planning scenario targets the stated fraction of the observed effect. The trial’s own original sample-size assumptions and justification are not reported in the registry record.

The 80% power column gives the illustrative number of participants per arm for a design that would have an 80% chance of detecting the effect used in that scenario, if the planning assumptions held and the effect were the one targeted. The 90% power column gives the corresponding per-arm number for a design with a 90% chance under those same assumptions. These are design calculations, not measures of what the completed trial achieved.

The figures rise as the targeted effect becomes smaller: detecting a smaller difference generally requires more participants because a small signal is harder to distinguish from random variation. For the primary endpoint, the planning illustration lists 17,752 participants per arm for 80% power and 23,764 participants per arm for 90% power when using 100% of the observed effect. For 75% of the observed effect, it lists 31,558 participants per arm for 80% power and 42,248 participants per arm for 90% power. For 50% of the observed effect, it lists 71,006 participants per arm for 80% power and 95,056 participants per arm for 90% power.

These figures are not observed power. They do not show the probability that the completed trial detected an effect, and they do not establish that a treatment effect exists. Because the observed estimate is close to zero, planning figures based on fractions of that estimate should be interpreted as illustrations tied to this particular observed contrast, not as a recommendation or as a reconstruction of the investigators’ design rationale. The registry record does not report the investigators’ original sample-size assumptions.

13. 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 = -0.020; pooled standard deviation σ = 0.673.
2. n = 2 × (1.96 + 0.842)² × 0.673² / -0.020² = 17,751.3, rounded up to 17,752 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 <- -0.02                      # observed difference in means
sigma <- 0.672552378310181                     # 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(2333630)
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 = 17,752 (80% power), 23,764 (90% power)
 75% of observed effect: n per arm = 31,558 (80% power), 42,248 (90% power)
 50% of observed effect: n per arm = 71,006 (80% power), 95,056 (90% power)
power.t.test: 17752.2 
Simulated power at n = 17,752 per arm: 0.802 (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.

14. Multiplicity, Missing Data and Analysis Populations

The registry lists several outcomes: emergency-room visits as the primary endpoint, and asthma exacerbations, hospitalizations, and frequency of use of the mobile application as secondary outcomes. Evaluating multiple outcomes can raise a multiplicity concern. In general, the more statistical comparisons that are made, the greater the chance that at least one result may appear unusual by chance alone. A prespecified primary endpoint helps identify the main comparison, but interpretation of secondary findings still depends on how outcomes and analyses were planned.

Whether the investigators prespecified a hierarchy for outcomes, adjusted for multiple comparisons, or treated secondary analyses as exploratory is not reported in the registry record. No multiplicity adjustment is reported. The registry record lists no reported analyses. The available unadjusted comparisons should therefore not be interpreted as if they were protected from the issues that can arise when many outcomes are examined.

The analysis population is also not reported in the registry record. The record does not say whether the primary analysis included all randomized participants, only participants with available outcome data, or a different population. It does not report whether an intention-to-treat approach, a per-protocol approach, or another rule was used. The outcome summaries give group sizes of 98 and 95, while enrollment is listed as 200; reasons for the difference are not reported in the registry record.

Missing-data methods are not reported in the registry record. There is no information about how many participants lacked six-month outcome data, why any data were missing, whether missingness differed by group, or whether imputation or sensitivity analyses were used. Without those details, readers cannot assess whether the posted summaries represent all randomized participants or whether incomplete follow-up could affect the comparison.

Other analysis details are also absent, including the planned model, covariate adjustment, handling of count distributions, and any interim analyses. These omissions do not show that a particular method was or was not used; they mean the details are not reported in the registry record. The unadjusted recalculations from the posted summaries should be read as limited descriptive comparisons rather than a complete account of the trial’s analysis.

15. 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 serious adverse-event figures list 98 participants at risk in the AsthmaCare group and 95 in the control group. The recorded number of serious adverse events affecting participants is 0 in each group. The deaths field is also 0 in each group. These figures describe what is recorded for the groups and denominators in the registry.

Zero recorded serious adverse events does not establish that no adverse events of any kind occurred, that every possible event was captured, or that the intervention is free of risk. The record also lists zero other adverse events affecting participants in both groups, but adverse-event collection methods and definitions are not described in the information available. No serious adverse-event terms are listed. The result should therefore be read as an absence of events recorded in these registry fields, not as a complete safety assessment or a comparison that rules out uncommon harms.

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

The posted primary result is a small difference between the two group means, with the AsthmaCare group’s mean number of emergency-room visits slightly lower than the control group’s mean. The unadjusted confidence interval spans zero, and the p-value is 0.837. Taken together, the summaries are compatible with a range of possible differences and do not establish a clear direction for the average visit count.

This does not show that the groups are equivalent. A finding that does not distinguish a difference from zero is not the same as evidence that any difference is absent or clinically unimportant. Equivalence or non-inferiority requires a specific design and prespecified margins, which are not reported in the registry record. Conversely, the observed mean difference alone does not establish that the app caused a change in emergency-room visits.

The trial’s randomized design is relevant to causal interpretation, but the registry does not provide enough detail about randomization procedures, outcome completeness, analysis populations, or planned analyses to evaluate all aspects of that interpretation. The outcome summaries include 98 participants in the app group and 95 in control, while the listed enrollment is 200. The registry record does not explain this difference or describe missing-data handling.

The secondary hospitalization outcome does not provide a clear, consistent directional pattern alongside the primary result, and quantitative results for some other listed secondary outcomes are not reported in the registry record. Multiple outcomes and unreported multiplicity handling further limit the weight that should be placed on isolated secondary findings. The safety fields record no serious adverse events or deaths in either group, but this does not prove the absence of all possible harms.

Overall, the registry supports a cautious description of the observed group summaries and their uncertainty, not a broad conclusion about whether AsthmaCare changes asthma outcomes. The findings are specific to the trial as documented, the six-month primary outcome, and the available posted results. They do not establish effects on outcomes or populations for which results or participant details are not reported.

17. Why This Trial Matters Statistically

This trial is statistically informative because it illustrates the difference between an observed estimate and the certainty that can be placed around it. The primary means are close, but that alone is not enough to establish equivalence. The confidence interval crosses zero, leaving uncertainty about whether the mean difference is negative, positive, or absent. A useful interpretation therefore considers the estimate and its precision together rather than relying only on the p-value.

The endpoint is a count of healthcare visits, summarized as a mean. This makes the analysis accessible but also raises general questions about the distribution of count data, variability, and whether the chosen method adequately represents the observations. The registry does not report diagnostics or a detailed analysis plan, so readers cannot determine how those statistical considerations were handled.

The trial also highlights why registry results must be read alongside reporting gaps. The record provides group summaries and a randomized design, but does not report the analysis population, missing-data approach, multiplicity strategy, or original sample-size justification. These are not minor technical details: they affect how securely the posted summaries can be linked to the randomized groups and how secondary comparisons should be interpreted.

Finally, the planning illustration demonstrates that sample-size calculations depend strongly on the effect targeted. Its figures use the observed effect as a starting point and are planning illustrations, not evidence about the probability that this completed trial detected an effect. Keeping the distinction between trial results and hypothetical future planning clear helps prevent a nonsignificant comparison from being misread as proof of no effect, or a planning figure from being mistaken for observed evidence.

18. 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 information. The current trial’s age range and detailed eligibility criteria are not reported in the registry record. The pilot study described in the summary involved children and teenagers, but that does not identify the population enrolled in the randomized trial. This limits assessment of which patients the results may represent.

The intervention and control conditions differed in the materials offered: AsthmaCare access in one group and a link to educational videos and information in the other. The record does not describe other care received, participant adherence, actual app-use frequency, or exposure to the control materials. Frequency of application use is listed as a secondary outcome, but quantitative results for it are not reported in the registry record.

The trial is listed as unmasked. The registry does not explain how emergency-room visits were collected or verified, whether outcome assessors were masked, or how awareness of assignment may have influenced reporting or follow-up. The randomization method and allocation-concealment details are also not reported.

The primary outcome summaries include 98 participants in AsthmaCare and 95 in control, whereas listed enrollment is 200. The registry does not explain the relationship between these figures, report the amount or reasons for missing data, or describe exclusions and withdrawals. The analysis population and missing-data methods are not reported. These omissions make it difficult to assess whether outcome data were complete and whether the group summaries preserve the randomized comparison.

The record does not report the original statistical plan, sample-size justification, multiplicity handling, interim analyses, or the method used by the investigators for the primary analysis. Quantitative results are also not reported for all listed secondary outcomes. These limitations constrain interpretation of both the primary comparison and the broader set of outcomes.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Randomized Prospective Trial of a Mobile Health Application for Asthma Self-Management — NCT02333630.
• Registry record last updated 2020-03-11; status last verified 2020-03.
• Results first posted 2020-03-11.
• 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.

22. Record Summary

NCT02333630 is a completed randomized, parallel-group trial of AsthmaCare mobile-app access compared with access to a website containing asthma education materials. The registry lists enrollment of 200 and no masking. The primary outcome is the number of emergency-room visits for asthma during the six months after enrollment and randomization.

The posted primary group means were 0.31 visits for AsthmaCare and 0.33 for control. The recalculated unadjusted mean difference was -0.02, with a confidence interval spanning zero and an unadjusted p-value of 0.837. The registry lists hospitalizations and other outcomes as secondary measures, but does not report quantitative results for every listed secondary outcome. Serious adverse events and deaths are recorded as 0 in both groups.

The registry record does not report the original sample-size rationale, analysis population, missing-data methods, or multiplicity approach. Interpretation should therefore focus on the posted summaries and their uncertainty, without treating the unadjusted comparison as a complete account of the trial’s statistical analysis.