Healthy And Positive Pathways for Young People With Type 1 Diabetes (HAPPY T1D): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Healthy And Positive Pathways for Young People With Type 1 Diabetes (HAPPY T1D) (NCT05413239), a randomized na study. The primary outcome is Time in Range (TIR).

2. Clinical Question

The clinical question combines a behavioral intervention with a measurable glycemic outcome. Diabetes distress and attitudes toward diabetes device use are listed as secondary outcomes, alongside A1c. These outcomes address related but distinct aspects of living with type 1 diabetes; they should not be treated as interchangeable with time in range.

The registry record describes a 2-year trial, with intervention sessions offered to the groups in different years. Its primary comparison is specifically the change through 12 months, before the Control Group begins sessions. The record does not report whether intervention effects on distress or device attitudes were observed, nor does it give outcome estimates for those measures. The available information therefore defines the study question and schedule, but does not establish the size or precision of any treatment-group difference.

3. Trial Design

HAPPY T1D is listed as a randomized, triple-masked, crossover trial with a planned duration of 2 years. The sponsor is Joslin Diabetes Center. The registry record lists the study as completed, an enrollment of 217, a start date of 2022-07-26, and a primary completion date of 2024-11-30. The phase is recorded as NA.

The timing of the intervention defines the crossover structure. The Intervention Group was scheduled to receive monthly intervention sessions during the first year. The Control Group was scheduled to receive no intervention sessions in that year, then receive monthly sessions during the second year after assessment of primary outcomes at 1 year. Thus the primary comparison is described for months 0-12, when the groups have different session schedules. Later measurements extend through 24 months, when both groups have had an intervention period, but the registry record identifies the months 0-12 comparison as the primary outcome analysis.

Random allocation is intended to make the groups comparable at the start, on average, so differences in subsequent outcomes can be interpreted in relation to assigned group, subject to missing data and other limitations. In a crossover design, the sequence and timing of treatment matter: later comparisons may reflect both the intervention period and when that period occurred. General crossover interpretation also considers whether an earlier intervention could have continuing effects into a later period. The registry record does not report a carryover assessment or a specific method for handling period or sequence effects.

Triple masking is recorded, but the registry record does not report who was masked or how masking was implemented. It also does not report the detailed allocation procedure, the analysis population, the statistical model, or the sample-size justification. Those details should not be inferred from the design labels. The intervention is classified as behavioral and described as psychoeducation to reduce diabetes distress and improve glycemic outcomes.

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: 26 participants consented but were not randomized (18 did not complete baseline data, 5 had an ineligible central lab A1c, 2 withdrew, and 1 was a sibling of a randomized participant)

Overall Study

Analysis population for the primary outcome, as defined in the registry: Some participants did not have CGM data at some time points, and thus there are some missing data.

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 Time in Range (TIR), measured over 0, 3, 6, 9, 12, 15, 18, 21, and 24 months (months 0-12 reported for primary outcome analysis).

The primary endpoint is time in range (TIR), expressed as the percent of time in the continuous glucose monitor glucose range of 70-180 mg/dL. The record says continuous glucose monitor data were to be downloaded every 3 months. The listed measurement schedule is 0, 3, 6, 9, 12, 15, 18, 21, and 24 months; the primary analysis timeframe is months 0-12.

The primary question concerns change in TIR from 0 to 12 months for the intervention group compared with the control group. As a continuous measure, TIR can represent how much of the monitored time a person's glucose readings fall within the specified range. It therefore summarizes glucose patterns across the monitoring period rather than relying on a single reading. This is a general description of the measure, not a claim about what happened in this trial.

The registry record specifies a mean and standard deviation as the parameter and dispersion measure. A group mean describes the average TIR in that group; a standard deviation describes variability among measurements around the mean. Interpreting a change comparison requires the reported group values, the estimated between-group contrast, and a measure of uncertainty. Those primary-result values are not reported in the registry record. The record does note that some participants lacked continuous glucose monitor data at some time points, which can affect how precisely and representatively the endpoint is estimated.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The outcome is continuous and is specified as a mean, with standard deviation as its measure of dispersion. General statistical interpretation separates an estimate of the average outcome from the variability of individual measurements. A mean can describe the central level in a group, while a standard deviation indicates how spread out observations are. Neither quantity alone establishes the difference between randomized groups; the comparison needs an estimate of the contrast and its uncertainty.

What does a change comparison estimate?

For this trial, the stated primary question compares change in TIR from 0 to 12 months between the Intervention Group and the Control Group. In general, comparing changes focuses on how outcomes shift over time within each group, then contrasts those shifts across groups. This differs from simply comparing measurements at one follow-up visit. The exact statistical implementation matters: for example, a model may handle repeated observations and baseline values in a particular way. The registry record does not report the model or the precise calculation used for the primary comparison, so it is not possible to say whether a specific adjustment or repeated-measures method was applied.

How should an estimate and confidence interval be read?

In general, an effect estimate describes the size and direction of a group contrast, while a confidence interval communicates uncertainty around that estimate. A narrower interval indicates greater precision under the assumptions of the analysis; a wider interval indicates more uncertainty. A confidence interval is not a guarantee that the true effect lies within its endpoints. The primary effect estimate and confidence interval are not reported in the registry record, so the precision of the primary comparison cannot be evaluated.

A p-value, when reported, addresses how compatible the observed data are with a specified null hypothesis under the statistical model. It does not measure the size or practical importance of an effect, and it does not replace an estimate with an interval. The registry record does not report a primary-outcome p-value or identify the test used. Therefore, neither statistical significance nor the absence of statistical significance can be inferred.

What does the crossover design change?

In a crossover design, the order and timing of treatment are part of the comparison. Here the groups are scheduled differently: the Intervention Group receives monthly sessions during year one, and the Control Group receives them during year two after the primary outcomes are assessed at 1 year. The first-year comparison is therefore between groups with different assigned session schedules. Later comparisons occur after the control group has also received sessions, so they do not represent the same contrast as the primary comparison.

As a general matter, crossover analyses may need to account for period effects, treatment sequence, and possible persistence of an earlier intervention's effects. The record does not state how these issues were analyzed. It also does not specify who was masked under the triple-masking designation or the methods used to preserve masking. No particular modeling approach or masking procedure should be assumed from the design label alone.

Why does variability matter?

Participants' TIR values can vary, and the standard deviation describes that spread. When variability is substantial relative to a group difference, an estimate may be less precise. Missing monitoring data can add uncertainty and may affect which observations contribute to the estimate. The registry record notes missing continuous glucose monitor data at some time points but does not report the amount of missingness or its distribution across visits and groups. It also does not report whether missing data were addressed using an imputation method, a model-based approach, or another strategy.

Over-dispersion is a general issue when observed variability exceeds what a chosen statistical model assumes. A model that does not adequately account for variability can produce uncertainty estimates that are too small or otherwise poorly calibrated. The registry record does not identify a model or report a dispersion assessment for this continuous endpoint, so there is no basis to say whether over-dispersion was examined or relevant in the trial's analysis.

What can be inferred from the planning assumptions?

The record describes sample-size illustrations based on a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with effects expressed as fractions of the observed effect. It also distinguishes participant counts per arm for ordinary outcomes from total event counts for time-to-event outcomes. These are planning illustrations, not observed power and not evidence that the original trial was designed using those assumptions. The registry record does not report the trial's own sample-size justification. The observed effect and the numerical illustration results are not reported in the registry record, so no sample-size values or achieved precision can be interpreted from those details.

In general, planning calculations depend on the chosen effect size, variability, allocation, significance threshold, and target power. They describe what a hypothetical design might require under its assumptions. They do not establish the probability that a completed trial has detected an effect, and they cannot substitute for the observed estimate and its confidence interval. The trial's enrollment of 217 is a design and enrollment fact; it does not by itself establish how precise the primary estimate is, especially with missing monitoring data and a crossover schedule.

Finally, a statistical analysis plan would ordinarily clarify the primary estimand, model, handling of missing values, analysis population, and multiplicity strategy. Those details are not reported in the registry record. The available description supports explanation of the design and endpoint, but not reconstruction of the analysis or independent verification of its assumptions.

10. Multiplicity, Missing Data and Analysis Populations

Multiplicity arises when several outcomes, time points, or statistical comparisons are examined. In general, testing many hypotheses can increase the chance that at least one result appears noteworthy by chance if no adjustment or prespecified hierarchy is used. This trial lists A1c, Diabetes Distress, and Attitudes Toward Diabetes Device Use as secondary outcomes, as well as four outcome measures and 17 analyses. The registry record does not report the full analysis list, identify which tests were confirmatory, or describe a multiplicity adjustment or testing hierarchy. The number of analyses alone is not enough to determine whether or how multiplicity was addressed.

The primary outcome is measured repeatedly, with assessments listed at 0, 3, 6, 9, 12, 15, 18, 21, and 24 months. The primary analysis timeframe is months 0-12, but the record does not report how the repeated measurements were incorporated into the model or how the primary contrast was selected from the available visits. The analysis method and any treatment of secondary outcome comparisons are not reported in the registry record.

For missing data, the record states that some participants did not have continuous glucose monitor data at some time points. It does not report the extent or pattern of missingness, reasons for missing observations, or the assumptions and procedures used to analyze them. General methods may include analyses based on available observations or methods that model or impute missing values, but no specific method can be attributed to this trial from the registry record.

The analysis population is also not reported in the registry record. It is therefore unclear from the available information which randomized participants contributed to each outcome analysis and how protocol deviations or incomplete follow-up were handled. These omissions limit assessment of the robustness and generalizability of any reported result. The primary results themselves are not reported in the registry record, so their sensitivity to missing data or multiplicity cannot be evaluated.

11. 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.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: hospitalization - diabetes-related (7.3%), hospitalization - not diabetes-related (6.2%).

The registry record lists serious adverse event figures separately for each group and study year. For the Intervention Group during Year 1 with intervention sessions, 4 serious adverse events are listed among 95 at risk. For the Intervention Group during Year 2 without intervention sessions, 6 are listed among 95 at risk. For the Control Group during Year 1 without intervention sessions, 13 are listed among 96 at risk. For the Control Group during Year 2 with intervention sessions, 8 are listed among 96 at risk. No deaths are listed in any of the four group-period entries, and no other adverse events are listed in those entries.

The registry also lists serious adverse event terms of Hospitalization - Diabetes-related at 7.3% and Hospitalization - Not diabetes-related at 6.2%. These percentages describe the listed terms; the record does not provide further detail about their calculation or timing. The group-period counts should be read within the schedule: intervention status changes by year for the Control Group, and the same group label across years does not represent an independent set of participants.

These figures are descriptive safety information, not a randomized comparison adjusted for follow-up time or other factors. The registry record does not report a statistical comparison of serious adverse events, event timing, severity details beyond the serious classification, or an attribution assessment. The counts alone do not establish whether events were caused by the intervention, nor do they support a comparative safety conclusion.

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

The record establishes that HAPPY T1D was designed to test a psychoeducational intervention in adolescents and young adults with type 1 diabetes, using change in continuous glucose monitor TIR as the primary outcome. It also establishes a randomized schedule in which the Intervention Group was offered monthly sessions during the first year and the Control Group was scheduled to receive them during the second year. These features clarify the intended question and the timing of the primary comparison.

The record does not establish the observed effect on TIR. It contains no reported primary estimate, group summaries, confidence interval, or p-value. Thus it cannot show the direction or size of the difference, how precisely it was estimated, or how compatible the data are with no difference. The completed status is not a substitute for posted results. Without those results, it is not possible to state whether the trial met its objective.

The secondary outcome names and the serious adverse event entries are also not enough to establish efficacy or comparative safety. Outcome names identify what was measured, not what values were observed. Safety counts are listed by group and year, but the record does not provide a comparative analysis or attribution assessment. They should not be interpreted as proof of benefit, absence of harm, or a causal relationship between sessions and events.

In general, a treatment-effect interpretation combines the estimate, its uncertainty, the analysis assumptions, and the completeness of outcome data. Here the record notes missing continuous glucose monitor observations but does not report how missingness was handled. It also does not report the analysis population, statistical model, or multiplicity strategy. These gaps constrain interpretation even before considering that the outcome estimates themselves are unavailable.

The trial's crossover schedule means that the first-year primary comparison and later follow-up address different timing contrasts. The control group receives intervention in year two, so later observations cannot be treated as a continuation of the same untreated comparison without considering period and sequence. The registry record does not report how later outcomes were analyzed. The most accurate conclusion is therefore about the study design and reporting: a completed randomized crossover trial with a specified continuous primary outcome is recorded, but its primary results and key analysis details are not reported in the registry record.

13. Why This Trial Matters Statistically

This trial raises statistical questions common to behavioral interventions and longitudinal clinical studies. The intervention is scheduled over time, outcomes are measured repeatedly, and the primary endpoint is a continuous measure derived from ongoing monitoring. Interpreting such a study requires attention to the treatment schedule, the time window that defines the primary contrast, the variability of the endpoint, and whether measurements are available for all participants at each visit.

The crossover schedule is especially relevant to the estimand: the primary comparison is defined in the first year, before the Control Group receives sessions. Later follow-up occurs under a different treatment history. Separating these contrasts is important because changes over time may reflect more than current intervention status. General analysis considerations include period effects, treatment sequence, and possible persistence of earlier intervention effects. The registry record does not report how these issues were handled.

Continuous glucose monitor data can provide repeated observations of time in a defined glucose range, while also creating practical challenges when data are missing at some visits. Missingness can affect both the amount of information available and the interpretation of the analyzed sample. The record acknowledges missing observations but does not describe their extent or analysis. This makes transparent reporting of the missing-data strategy important for assessing precision and potential bias.

The registry also lists several secondary outcomes and multiple analyses. That breadth can help characterize outcomes beyond TIR, but it makes a clear distinction between primary and secondary questions and a transparent multiplicity strategy important. The number of analyses is not itself evidence of selective reporting; the detailed plan and results are needed to evaluate that question, and they are not reported in the registry record.

Finally, statistical significance alone would not describe the importance or precision of an effect. A reader needs the estimated group difference and its confidence interval, together with methods and missing-data information. Those primary results are not reported in the registry record. The design is statistically informative as a framework, but the absent outcome estimates prevent assessment of what the trial observed.

14. 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 most consequential limitation of the registry information is that the primary outcome results are not reported in the registry record. Although the trial is marked completed and the endpoint is defined, there are no group means, standard deviations, change estimates, between-group effect estimates, confidence intervals, or p-values for the primary comparison. The magnitude, direction, and precision of the result therefore cannot be evaluated.

The record acknowledges missing continuous glucose monitor data at some time points, but does not quantify missingness or describe its pattern, causes, or handling. Without those details, it is not possible to assess whether the analysis relied on available observations, used a method for missing values, or tested sensitivity to assumptions about the missing data. The analysis population is not reported either.

The statistical model and analysis plan are not described in enough detail to determine how repeated measures, baseline values, or the crossover structure were handled. The record does not explain whether period, sequence, or carryover effects were considered, nor does it describe who was masked under the triple-masking designation. A sample-size justification for the original trial is not reported in the registry record; planning illustrations do not establish the trial's original design rationale or observed power.

The record names secondary outcomes and reports a count of analyses, but does not give their estimates or explain how multiple comparisons were addressed. The safety information is also limited: group-period figures and serious event terms are listed, but a comparative analysis and attribution assessment are not reported. These limitations concern what the registry record makes available; they do not establish that the trial failed to conduct analyses or collect additional information.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Healthy And Positive Pathways for Young People With Type 1 Diabetes (HAPPY T1D) — NCT05413239.
• Registry record last updated 2026-03-12; status last verified 2026-03.
• Results first posted 2026-03-12.
• 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.

18. Record Summary

HAPPY T1D (NCT05413239) is a completed randomized, triple-masked crossover trial sponsored by Joslin Diabetes Center. The registry record lists 217 enrolled participants with type 1 diabetes, aged 14-25 years. The study start date is 2022-07-26, and the primary completion date is 2024-11-30. The phase is recorded as NA.

The behavioral intervention consists of monthly psychoeducational sessions. The Intervention Group was scheduled to receive sessions in year one; the Control Group was scheduled to receive them in year two, after primary outcome assessment at 1 year. The primary outcome is change in mean continuous glucose monitor time in range, defined as percent of time at 70-180 mg/dL, from 0 to 12 months. A1c, Diabetes Distress, and Attitudes Toward Diabetes Device Use are listed as secondary outcomes.

The record notes missing continuous glucose monitor data at some time points and lists serious adverse event figures by group and year. It does not report the primary outcome estimates, uncertainty measures, detailed statistical analysis methods, missing-data methods, or multiplicity strategy. The design and outcomes are described, but the trial's primary results are not reported in the registry record.