This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Testing a Digital Intervention for Adolescents (NCT04567888), a randomized na study. The primary outcome is Change in Perceived Stress [Perceived Stress Scale (PSS)].
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT04567888 |
| Phase | NA |
| Condition | Rumination, Stress, Psychological |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | None (open label) |
| Enrollment | 353 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Happify Inc. |
| Results posted | Yes |
2. Clinical Question
Population
The study concerns teen participants ages 13–17. The registry record lists rumination and psychological stress as conditions. It does not report further eligibility details or a more specific description of the population used in the primary outcome analysis.
Intervention
The intervention was Happify Teens, described as a digital well-being intervention accessed through a mobile application or web browser. The registry summary describes an 8-week intervention period.
Comparator
The comparison group was a waitlist control condition. The registry does not describe additional activities or services for that group beyond its waitlist designation.
Primary question
The primary outcome was change in perceived stress measured with the Perceived Stress Scale (PSS). The clinical question is whether the recorded PSS scores changed over the assessment schedule and how the intervention-arm pattern compared with the waitlist pattern. The registry record does not report a single comparative estimate, its uncertainty, or a statistical test for that question.
The trial was randomized and used parallel groups, so the intended comparison was between participants assigned to the digital intervention and participants assigned to the waitlist condition. That design can support a comparison of outcome patterns between assigned groups, provided the analysis and follow-up data are adequately reported. The available registry entries establish the question and the measure, but not the size or precision of any observed difference.
3. Trial Design
The registry record describes a randomized, parallel-group study with no masking. Participants were assigned to Happify Teens or a waitlist control. The intervention is described as a digital well-being program available through an application or web browser. The record describes an 8-week intervention period and a 1-month follow-up period. Its listed PSS assessment times are baseline, 4 weeks, 8 weeks, and 12 weeks.
Enrollment is recorded as 353. That figure is the registry enrollment value; group-specific enrollment and analysis counts are not reported in the registry record. The allocation ratio, method used to generate the random sequence, concealment of assignment, and any stratification factors are also not reported in the registry record. Because masking is listed as none, participants and study personnel were not masked according to the registry entry. Who knew assignment during outcome assessment or data analysis is not separately described.
The study status is completed. The recorded start date is 2021-06-03, and primary completion is recorded as 2022-03-13. The phase is listed as NA. Happify Inc. is named as sponsor. These administrative details describe the registry record; they do not establish when every participant completed each assessment or whether all planned data were analyzed.
The primary endpoint is a continuous score, and the registry describes change in that score across several assessment times. A repeated-measures comparison could address patterns over time, but the statistical model and the particular contrast used are not reported in the registry record. The record also does not report a single primary time point or a numerical estimate comparing groups at any one of the listed times. The details therefore establish the design and the measurement schedule, but are insufficient to reconstruct the analysis.
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
| Stage | Happify Teens | Waitlist Control |
|---|---|---|
| STARTED | 178 | 175 |
| COMPLETED | 132 | 171 |
| NOT COMPLETED | 46 | 4 |
Reasons for not completing this period:
| Reason | Happify Teens | Waitlist Control |
|---|---|---|
| Did Not Create Happify for Teens Account | 22 | 0 |
| Did Not Complete Any Happify for Teens Activities | 22 | 0 |
| Reported Unusual Birth Year | 2 | 3 |
| Duplicate Responses | 0 | 1 |
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.
| Characteristic | Unit | Happify Teens | Waitlist Control | Total |
|---|---|---|---|---|
| Participants analysed | 178 | 175 | 353 | |
| Age, Customized: 13 years | Participants | 19 | 24 | 43 |
| Age, Customized: 14 years | Participants | 44 | 42 | 86 |
| Age, Customized: 15 years | Participants | 30 | 31 | 61 |
| Age, Customized: 16 years | Participants | 36 | 43 | 79 |
| Age, Customized: 17 years | Participants | 47 | 32 | 79 |
| Age, Customized: Missing or Unusual Birth Year | Participants | 2 | 3 | 5 |
| Sex/Gender, Customized: Female | Participants | 122 | 110 | 232 |
| Sex/Gender, Customized: Male | Participants | 42 | 50 | 92 |
| Sex/Gender, Customized: Non-Binary/Other | Participants | 14 | 14 | 28 |
| Sex/Gender, Customized: Missing | Participants | 0 | 1 | 1 |
| Ethnicity (NIH/OMB): Hispanic or Latino | Participants | 19 | 22 | 41 |
| Ethnicity (NIH/OMB): Not Hispanic or Latino | Participants | 159 | 153 | 312 |
| Ethnicity (NIH/OMB): Unknown or Not Reported | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 3 | 1 | 4 |
| Race (NIH/OMB): Asian | Participants | 3 | 2 | 5 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Black or African American | Participants | 9 | 11 | 20 |
| Race (NIH/OMB): White | Participants | 140 | 138 | 278 |
| Race (NIH/OMB): More than one race | Participants | 17 | 15 | 32 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 6 | 8 | 14 |
| Region of Enrollment: United States | participants | 178 | 175 | 353 |
| Perceived Stress Scale | score on a scale | 26.06 (SD 4.41) | 25.29 (SD 5.04) | 25.68 (SD 4.74) |
| Ruminative Responses Scale - Brooding Subscale | score on a scale | 14.18 (SD 2.32) | 14.29 (SD 2.55) | 14.23 (SD 2.44) |
6. Primary Endpoint
The registry lists the primary outcome as Change in Perceived Stress [Perceived Stress Scale (PSS)], measured over Baseline, 4 weeks, 8 weeks, 12 weeks.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Standard Deviation |
| Unit | score on a scale |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is change in perceived stress measured by the Perceived Stress Scale (PSS). The registry describes the PSS as a 10-item measure. Each item asks how often a participant felt stressed by a statement during the following month, with response values ranging from never (0) to very often (4). The total score can range from 0 to 40, with higher scores indicating higher perceived stress.
A score on a continuous scale retains information about the degree of a participant’s reported stress rather than reducing responses to a simple yes-or-no category. In general, continuous measures can be summarized by means and standard deviations: the mean describes the central value in a group, while the standard deviation describes variability among scores. The registry lists the endpoint parameter as a mean and its dispersion as a standard deviation.
Perceived stress is the construct chosen for the primary outcome, and the repeated assessments allow its recorded level to be considered over the course of the intervention and follow-up. The PSS schedule is baseline, 4 weeks, 8 weeks, and 12 weeks. The registry record does not explain why this measure or these particular assessment times were selected, nor does it report a threshold for a clinically meaningful change.
The endpoint title refers to change, but a change estimate requires a defined comparison, such as change from baseline at a specified time or a group-by-time contrast. The registry record does not report a single comparison of this kind. It therefore does not establish the direction, magnitude, or precision of a difference in PSS change between the assigned groups.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record identifies a randomized comparison of Happify Teens with a waitlist control and specifies change in PSS score as the primary outcome. It also lists four PSS assessment times: baseline, 4 weeks, 8 weeks, and 12 weeks. These details define the intended clinical question, but they do not provide the outcome values needed to answer it quantitatively.
No group means, standard deviations, change estimates, confidence intervals, or p-values for the primary outcome are reported in the registry record. The record notes that the primary outcome has several categories or time points and was not reduced to one comparison. Consequently, it is not possible from this record to state whether the groups differed at a particular assessment, how large any difference was, or how precisely it was estimated. A completed study status does not itself supply evidence about the outcome.
For a continuous outcome, an estimated between-group contrast would describe the difference in average scores under a specified analysis. A confidence interval would indicate the range of values reasonably compatible with the estimate under the model and assumptions used. Neither the estimate nor its interval is reported for the primary outcome. Without them, the size and uncertainty of any effect cannot be evaluated. A p-value alone, even if available, would not describe the magnitude or practical importance of a difference; here, no primary p-value is reported either.
The assessment schedule raises an interpretive issue because change can be defined in more than one way. One analysis might compare groups at a particular follow-up while accounting for baseline values; another might estimate a pattern across all visits. These approaches answer related but not identical questions. The registry record does not identify which contrast or model was used, and does not specify one time point as the sole primary comparison. The listed schedule should therefore not be treated as evidence that any specific comparison was prespecified or performed.
The registry reports 353 enrolled, but does not report group-specific numbers, numbers assessed at each visit, or the numbers included in each outcome analysis. Without those details, readers cannot assess attrition, the amount of available outcome data, or the analysis denominator. The record also does not describe an analysis population, such as whether participants were analyzed according to assignment regardless of adherence.
The statistical interpretation is therefore limited to the trial’s design and intended measurement. Randomization describes the planned basis for group assignment, while the outcome results needed to estimate a treatment contrast are not reported in this registry record. No conclusion about the size, direction, statistical evidence, or clinical importance of a group difference can be drawn from the recorded details alone.
9. Statistical Methods Explained
The registry classifies the primary outcome as continuous and identifies the mean as its summary parameter, with standard deviation as the dispersion measure. These choices describe how scores may be summarized, but they do not identify the actual statistical model used. The registry record does not report a model, a contrast, an adjustment set, a confidence interval, or a primary-outcome test.
What does a mean and standard deviation describe?
In general, a mean is an average that provides a summary of the location of continuous scores. A standard deviation describes how spread out individual scores are around that average. These summaries are useful for understanding a group’s score distribution, but a mean and standard deviation alone do not describe a between-group effect. For that, an analysis must define a contrast between groups, and, for a change outcome, specify how baseline and follow-up scores are used.
Means and standard deviations can be sensitive to unusually high or low values. Whether that matters depends on the score distribution and the analysis assumptions. The registry does not report score distributions, diagnostics, or any alternative summaries. It is therefore not possible to assess whether the selected summary adequately describes the observed PSS data.
How can repeated measurements be analyzed?
General statistical practice offers several ways to analyze measurements collected from the same participant at multiple visits. A model may estimate group differences at selected visits, a difference in change from baseline, or an overall pattern across time. Repeated-measures models account for the fact that measurements from one participant are related to one another; they are not independent observations. A model must also state how time is represented and what comparison is the target.
The PSS assessment times listed in the record are baseline, 4 weeks, 8 weeks, and 12 weeks. The record does not specify whether the primary analysis used one follow-up, all follow-ups, or an overall group-by-time test. It also does not say whether baseline was modeled as an outcome measurement, used as an adjustment variable, or handled in another way. Those distinctions affect the estimand and interpretation, so none should be assumed from the endpoint title alone.
Why does uncertainty matter?
In general, a confidence interval expresses uncertainty around an estimated effect under a specified statistical model. A narrow interval indicates greater precision than a wide interval, though the practical meaning still depends on the scale and the range of values considered important. The registry record does not report a primary effect estimate or confidence interval. The precision of any PSS comparison therefore cannot be evaluated from the recorded information.
A p-value is a measure tied to a statistical test and its null hypothesis; it is not a measure of effect size and does not indicate the probability that a hypothesis is true. It is most informative when interpreted alongside the estimate, interval, analysis plan, and study context. No primary p-value is reported in the registry record, and the record does not identify the test used. Statistical significance, if reported elsewhere, should not be inferred from the completion status or from the existence of a randomized design.
What is over-dispersion, and is it relevant?
In general, over-dispersion describes variability greater than a statistical model expects. It is a concern in some count or binary outcome models when their variance assumptions do not match the data. The primary outcome is a continuous PSS score summarized by a mean and standard deviation, so count-model over-dispersion is not the central issue described by the endpoint. The registry record does not report a model or diagnostics from which any distributional concern could be assessed.
What can the planning assumptions tell us?
The registry record describes a planning illustration based on an observed effect, with a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation. It specifies that the effect to detect is a stated fraction of the observed effect. Such assumptions define a hypothetical planning exercise; they do not establish the trial’s original design rationale, actual power, or the effect observed in the trial. The registry does not report the planning outputs or a sample-size justification for the trial’s own design. Planning illustrations are not observed power and cannot substitute for an effect estimate with its uncertainty.
The statistical analysis plan, including model specification, handling of repeated measures, covariates, confidence-interval method, and testing strategy, is not reported in the registry record. The number of analyses is recorded as 2, but their full specifications and relationship to the primary endpoint are not stated. Thus, the record supports an explanation of the outcome type and general analytical choices, but not a reconstruction or independent assessment of the statistical analysis.
10. Multiplicity, Missing Data and Analysis Populations
Multiplicity arises when more than one outcome, time point, contrast, or statistical test is considered. In general, conducting multiple tests can increase the chance of obtaining at least one result that appears statistically notable by chance, unless the testing strategy accounts for the number and relationship of the comparisons. An analysis plan may identify one primary contrast or use a multiplicity adjustment. The registry record does not report such a strategy.
The record lists the primary PSS outcome at baseline, 4 weeks, 8 weeks, and 12 weeks, and notes that it was not reduced to one comparison because it has several categories or time points. It also lists change in rumination on the Ruminative Responses Scale-Short Form-Brooding Subscale as a secondary outcome. Two outcome measures and two analyses are recorded. The detailed hypotheses, contrasts, hierarchy of outcomes, and any adjustment for multiple testing are not reported in the registry record. The count of analyses alone does not establish which tests were performed or how their results were interpreted.
Missing-data information is also not reported. The record does not give the number of PSS observations available at each visit, the amount or pattern of missingness, reasons for missing assessments, or the method used to handle missing scores. In general, missing-data methods rely on assumptions about why measurements are absent; conclusions can depend on whether those assumptions are plausible. Without follow-up counts and the analysis method, readers cannot assess how missing outcome data may affect the estimates.
The analysis population is not reported in the registry record. It is therefore unclear whether participants were analyzed according to randomized assignment, according to intervention received, or under another rule. Group-specific analysis counts and adherence information are not reported either. These omissions limit the ability to judge how closely an analysis reflects the randomized comparison and how representative the analyzed participants are of those enrolled.
11. What the Result Does, and Does Not, Mean
The registry record establishes that this was a completed randomized study of Happify Teens against a waitlist control, with change in perceived stress as the primary outcome. It identifies the PSS scale, its score range and interpretation, and the planned assessment schedule. Those details describe what the study set out to measure, not what the comparison found.
No primary comparative estimate, group-level outcome summary, confidence interval, or p-value is reported in the registry record. Accordingly, the record does not show whether PSS scores changed differently between assigned groups, how large a difference may have been, or how uncertain it was. It also does not support a conclusion about the clinical importance of any possible difference. No claim that the intervention did or did not work follows from these registry entries.
In general, a statistically estimated difference and its practical importance are separate questions. Interpretation requires the effect’s direction and magnitude, its uncertainty, the measurement scale, and a meaningful context for judging the size of change. The registry does not report a threshold for meaningful change on the PSS or any comparison estimate. A score range alone does not supply that threshold.
The randomized design is relevant because random assignment is intended to make groups comparable at the outset, but it does not by itself answer questions about follow-up, missing data, adherence, or analysis choices. The record does not report group-specific outcome counts, treatment exposure, or analysis populations. The absence of these details limits assessment of how the intended comparison was carried out.
The registry’s completed status should be read as a study status, not as a result. Likewise, the enrollment value does not tell readers how many participants contributed to each endpoint analysis. The recorded adverse-event fields list zero participants at risk and zero affected in both the serious and other adverse-event categories, with zero deaths. Because the at-risk entries are zero, these records do not provide an interpretable denominator for judging the completeness of adverse-event reporting or the occurrence of events among participants.
The most defensible meaning is therefore narrow: the record documents a trial design and a planned primary measure, while the numerical outcome evidence and several analysis details are not reported in the registry record. Further conclusions require outcome estimates and methods information that are absent from this record.
12. Why This Trial Matters Statistically
This trial is statistically informative as an example of how a clear randomized design and a defined outcome do not, by themselves, provide enough information to interpret an effect. The registry names the population, intervention, comparator, continuous primary measure, and assessment schedule. Those elements frame a clinical question, but readers also need the actual group results and the analysis that connects them to that question.
The repeated PSS assessments make the definition of change especially important. A comparison at one visit, a comparison of change from baseline, and an overall comparison of patterns across visits represent different estimands. Reporting a prespecified primary contrast would help readers understand which question the analysis addresses. The registry record does not identify a single comparison among the listed time points.
The record also illustrates why precision and missingness belong in interpretation. A point estimate without an interval can obscure uncertainty, while an analysis without visit-specific counts can make attrition difficult to assess. For a randomized comparison, readers benefit from knowing how many participants contributed to each outcome, how missing observations were handled, and whether analysis followed assignment. Those details are not reported in the registry record.
Finally, planning calculations and observed results serve different purposes. The record describes general assumptions for planning illustrations, but those assumptions cannot establish the effect observed in this trial or its precision. A statistical interpretation depends on reported estimates and their uncertainty, not on a planning scenario or study completion status. The available details are enough to define the intended study question, but not to evaluate the magnitude or reliability of its primary outcome finding.
13. 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 registry entries for this trial. First, masking is listed as none. Knowledge of group assignment may affect participants’ expectations, engagement, reporting, or other aspects of a self-reported stress score. This is a general design consideration rather than evidence that bias occurred. The registry record does not describe procedures intended to reduce or assess such effects.
Second, the comparator is a waitlist condition. That identifies the assigned comparison but does not indicate that the groups received equivalent attention or contact. The registry does not describe what participants in the waitlist group did during the intervention period. The contrast therefore cannot be assumed to isolate the digital platform from every other difference between assigned conditions.
Third, the population description is limited to teen participants ages 13–17 and the listed conditions of rumination and psychological stress. The registry record does not report additional eligibility criteria, baseline characteristics, or recruitment details. The extent to which enrolled participants represent adolescents beyond the study population cannot be assessed from these details.
Fourth, the primary outcome has multiple assessment times, and the registry notes that it was not reduced to one comparison. Without a stated primary contrast, analysis model, and multiplicity strategy, readers cannot determine which time-specific or overall question was intended to carry the main interpretation. The record also lacks group-specific follow-up counts and missing-data methods, leaving the completeness of the repeated outcome data unclear.
Finally, the adverse-event fields list zero at risk and zero affected in both arms for serious and other adverse events, as well as zero deaths. The zero at-risk entries make those fields insufficient for assessing event frequency or completeness of surveillance. These limitations concern what can be evaluated from the registry record; they do not establish that a particular bias, missingness pattern, or event occurred.
14. Related Tutorials
15. Related Statistical Calculators
16. Sources
- ClinicalTrials.gov: Testing a Digital Intervention for Adolescents — NCT04567888.
- Registry record last updated 2024-08-15; status last verified 2024-03.
- Results first posted 2024-08-15.
- 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.
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17. Record Summary
The registry record describes a completed randomized, parallel-group trial with no masking, comparing Happify Teens with a waitlist control among teen participants ages 13–17. The recorded enrollment is 353, and the sponsor is Happify Inc. The study is listed as completed, with a start date of 2021-06-03 and primary completion date of 2022-03-13; phase is listed as NA.
The primary outcome is change in perceived stress measured by the PSS, a 10-item scale with scores from 0 to 40 and higher scores indicating higher perceived stress. Assessments are listed at baseline, 4 weeks, 8 weeks, and 12 weeks. The registry also lists change in rumination as a secondary outcome.
A single comparative primary result, including an estimate and its uncertainty, is not reported in the registry record. Group-specific analysis counts, missing-data methods, and the detailed statistical analysis plan are also not reported. The record defines the study question and outcome schedule but does not establish the direction, magnitude, or precision of the primary comparison.