Improving Health Communication During the Transition From Pediatric to Adult Diabetes Care: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Improving Health Communication During the Transition From Pediatric to Adult Diabetes Care (NCT03734107), a randomized na study. The primary outcome is Hemoglobin A1c.

2. Clinical Question

The study rationale is that the transition to adult diabetes care coincides with greater responsibility for independent self-care. The registry describes communication with health care providers as a potentially important part of diabetes self-care during this transition. PREP-DC was intended to support communication skills, including preparing for clinic visits, discussing diabetes-related concerns, and reviewing glucose data. The clinical question examined in the posted primary result is narrower than that broader rationale: it concerns the A1c means at the stated follow-up and the estimated mean difference between the randomized groups. Other medical, communication, and psychosocial measures are mentioned in the study summary, but additional results for them are not reported in the registry record.

3. Trial Design

The registry describes a randomized, parallel-group study with single masking. It is marked completed, with a start date of 2018-11-06 and a primary completion date of 2023-12-01. The phase is listed as NA. The condition is type 1 diabetes mellitus, and the sponsor is Children's National Research Institute. These registry descriptors establish the broad design, but do not provide all details needed to evaluate how randomization or masking was implemented.

The planned comparison was PREP-DC versus standard care. The intervention description includes 3 sessions with study interventionists, text messages, and other resources during the active intervention period. The standard-care description includes regular diabetes clinic visits and standard materials on transition to adult diabetes care. The registry lists enrollment as 52. Separately, its arm descriptions state that 50 participants would be randomized to each condition. The record does not explain the relationship between those planned arm counts and the enrollment entry, so they should not be treated as a single reconciled account of enrollment.

The primary endpoint results concern A1c at 8 months post-baseline. The outcome record says that 37 participants had A1c data at final follow-up, with 17 in the PREP-DC group and 20 in the standard-care group contributing to the posted means. These are outcome-specific counts, not a statement about the full randomized population. Reasons for participants lacking A1c data, and the analysis population used for the sponsor's primary analysis, are not reported in the registry record. Details such as the randomization procedure, allocation concealment, masking roles, and any deviations from the intended intervention are also not reported in the registry record.

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: Letters were sent to 187 adolescents and young adults. Fifty-two participants completed all baseline procedures and were enrolled and randomized.

Overall Study

Analysis population for the primary outcome, as defined in the registry: 37 participants had A1c data at final follow up.

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.

Population: 52 participants were randomized to the PREP-DC Intervention (n=26) or Standard Care Comparison (n=26) groups.

6. Primary Endpoint

The registry lists the primary outcome as Hemoglobin A1c, measured over 8 months post-baseline.

The primary endpoint is hemoglobin A1c, reported as an A1c percentage. A1c reflects the percentage of glycated hemoglobin and is used as a measure of glycemic control over time. In a study of transition support for people with type 1 diabetes, it provides a clinical outcome that is distinct from measures of communication, clinic engagement, or transition readiness. The registry lists the assessment timeframe as 8 months post-baseline.

The posted outcome is the group mean, accompanied by a standard deviation. A mean describes the average A1c among participants with data in that group; it does not describe every participant's value. A standard deviation describes the spread of individual values around the group mean. Greater spread means participant measurements vary more within that group, while a smaller spread means they are more closely clustered around the mean. These summaries do not show the full distribution, individual trajectories, or whether changes from baseline differed between groups.

The registry's primary-outcome description reports that 37 participants had A1c data at final follow-up. The posted means are 7.988 for PREP-DC and 8.025 for standard care. Because the reported endpoint is a continuous measure, the primary contrast is expressed as a difference in group means. The endpoint is relevant to the study's stated interest in glycemic control, but it does not capture every aspect of the transition experience described in the study rationale.

7. Results Posted in the Registry

• PREP-DC Intervention: mean 7.99 versus 8.03 on control; difference -0.04 (95% CI -1.15 to 1.08), standardized effect d = -0.02; z-test p = 0.948.

8. Statistical Interpretation

9. Statistical Methods Explained

What does a mean difference represent?

For a continuous outcome, a mean difference compares the average measurement in one group with the average in another. The posted contrast is PREP-DC minus standard care. A negative estimate therefore indicates a lower observed mean in PREP-DC, while a positive estimate would indicate a higher observed mean. The estimate of -0.037 is the point estimate: it is the single value that best summarizes the observed contrast under this simple comparison. It does not, by itself, show how stable that estimate might be if the study were repeated.

Here, the group means are 7.988 and 8.025, and the posted mean difference is -0.037. These are summaries of the endpoint data, not a comparison of changes from baseline. A comparison of final means and an analysis of change can answer different questions, especially if the groups differed at baseline. Baseline outcome summaries and the sponsor's planned primary analysis are not reported in the registry record, so the posted contrast should not be described as a baseline-adjusted effect or as a change-score result.

What do the standard deviations describe?

The standard deviation describes how dispersed individual measurements are around a group's mean. For this outcome, the posted standard deviations are 1.996 in PREP-DC and 1.345 in standard care. They are measures of participant-level variation, not measures of uncertainty in the mean difference. The uncertainty in a group mean also depends on how many observations contribute; the uncertainty in a contrast depends on the information from both groups and on the analysis method. A standard deviation should not be interpreted as a confidence interval or as a range containing every participant's result.

Variation matters because a mean difference is estimated from individual measurements that are not all alike. When variation is substantial relative to the contrast being estimated, the point estimate can be imprecise. The reported interval reflects uncertainty in the difference, whereas the standard deviations describe the spread within each group. These quantities serve related but distinct purposes.

How should the p-value be understood?

The unadjusted p-value is 0.948. In general, a p-value assesses how unusual data at least as incompatible with a specified null model would be if that model and the test assumptions were correct. For a group-mean comparison, the null model commonly concerns no difference in the population means, but the exact null hypothesis and test procedure used for the registry's comparison are not reported in the registry record. The value is not a measure of the size or clinical importance of the contrast. It also does not tell whether the study had enough information to rule out effects that might matter.

The registry's comparison is labeled unadjusted, and no analysis entries are listed. The record does not report the statistical test, whether covariates were included, how missing endpoint data were handled, or whether the posted comparison reproduces the sponsor's prespecified analysis. The result should therefore be read as a summary-statistic comparison, not as evidence that a particular model or analysis plan was used.

Why does the confidence interval add information?

A confidence interval pairs an estimate with a range reflecting its statistical uncertainty under a specified method. It conveys more than a point estimate by showing which values are consistent with the data at the interval's stated level. The interval associated with this mean difference extends from -1.154 to 1.08 and includes zero. The interval's level and calculation method are not reported in the registry record, so those details cannot be independently assessed from the registry entry alone. Its breadth makes clear that the estimate is not precise enough to settle the direction or size of the difference.

In general, a narrower interval indicates greater precision, while a wider interval indicates greater uncertainty. Precision depends on factors such as the amount of outcome information and the variability of measurements. It is distinct from statistical significance: a point estimate can be small, and its interval can still allow a range of substantially different values. Conversely, a point estimate should not be treated as a precise result simply because it has been calculated to several decimal places.

What can be said about the analysis population?

The outcome record states that 37 participants had A1c data at final follow-up, with 17 contributing to the PREP-DC mean and 20 to the standard-care mean. The registry does not state whether the primary analysis used all randomized participants, only participants with observed follow-up data, or another analysis population. It does not report an imputation method, a missing-data sensitivity analysis, or reasons for missing A1c measurements. This matters because an analysis restricted to observed outcomes can be affected if missingness is related to outcomes or differs meaningfully between groups. The available information does not establish whether such concerns affected this result.

General statistical interpretation also distinguishes the effect of assignment from the effect of receiving or completing an intervention. Randomization can support a comparison based on assigned groups when analyzed appropriately, but the registry does not report adherence, intervention completion, or the sponsor's analysis population. The posted group summaries therefore cannot be assumed to represent a particular intention-to-treat or per-protocol analysis.

What is not documented?

The registry record does not report the sample-size justification or original design assumptions, the sponsor's detailed statistical plan, interim analyses, adjustment for multiple outcomes, or the method used to form the interval and p-value. The sample-size planning figures associated with the observed effect are a separate illustration, not documentation of how the trial was originally designed. These absent details limit assessment of whether the posted comparison followed a prespecified analysis and how it was intended to address other study outcomes.

10. Confidence Intervals and Precision

The mean-difference estimate is -0.037 A1c percentage points, with a reported interval from -1.154 to 1.08. The interval includes zero, so the posted results do not precisely determine whether the population mean is lower or higher in PREP-DC than in standard care. The interval also spans values that are considerably farther from zero than the point estimate. Thus, the central estimate is close to no difference, but the data remain compatible with a broad range of possible contrasts.

A confidence interval communicates uncertainty under the method used to calculate it. Its width is important: narrow intervals generally indicate more precision, while wide intervals leave greater uncertainty about the effect's size and direction. Here, the reported interval is wide relative to the point estimate. The group means alone would conceal this uncertainty, and the p-value alone would not show the range of contrasts compatible with the data.

The registry does not report the interval's confidence level or calculation method. It also does not report a detailed primary analysis plan, adjustments, or how missing outcome data were handled. Those omissions mean that the interval can be described as posted but its construction cannot be fully evaluated from the registry record. The outcome-specific group counts are 17 for PREP-DC and 20 for standard care; the registry states that 37 participants had final-follow-up A1c data. These counts and the posted standard deviations provide context for the limited precision, but they do not identify the source or pattern of missing data.

Precision is not the same as whether an estimate is clinically important. The interval does not establish equivalence, and the result should not be interpreted as demonstrating that the groups had the same A1c. It instead indicates that this estimate leaves substantial uncertainty about the contrast.

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 sample-size planning figures are expressed as participants per arm, not as total event counts. They are planning illustrations calculated from the observed effect, rather than the trial's original design justification. The listed assumptions are a two-sided significance level of 0.05, equal allocation between the arms, and a normal approximation. The effect to detect is specified as a fraction of the observed effect. The original design assumptions and sample-size justification are not reported in the registry record.

The 80% power column gives the planned participants per arm under those assumptions for a design with an 80% chance of detecting the specified effect if that effect were the true one and the assumptions held. The 90% power column gives the corresponding per-arm planning figure for a design with a 90% chance under those conditions. These are prospective planning concepts; neither column describes the probability that the completed study found an effect.

For planning for 100% of the observed effect, the figures are 32,145 participants per arm for 80% power and 43,033 participants per arm for 90% power. For planning for 75% of the observed effect, they are 57,146 and 76,502 participants per arm, respectively. For planning for 50% of the observed effect, they are 128,578 and 172,129 participants per arm, respectively. Smaller target effects require more participants under the stated assumptions, because a smaller difference is harder to distinguish from random variation.

The associated curve should be read as expressing this same relationship between the target effect and the required per-arm planning size, not as a projection of this trial's observed outcomes. The estimates are illustrations based on the observed effect, not observed power. They do not show that the completed study had a particular probability of detecting an effect, and they should not be confused with the registry's enrollment or outcome-specific counts.

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 = -0.037; pooled standard deviation σ = 1.674.
2. n = 2 × (1.96 + 0.842)² × 1.674² / -0.037² = 32,144.4, rounded up to 32,145 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 <- -0.0369999999999999                      # observed difference in means
sigma <- 1.67430779727026                     # 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(3734107)
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 = 32,145 (80% power), 43,033 (90% power)
 75% of observed effect: n per arm = 57,146 (80% power), 76,502 (90% power)
 50% of observed effect: n per arm = 128,578 (80% power), 172,129 (90% power)
power.t.test: 32145.3 
Simulated power at n = 32,145 per arm: 0.800 (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 study summary mentions several kinds of data, including A1c, glucose monitoring frequency, communication quality, health care engagement, and depressive symptoms. The registry lists 4 outcome measures, but secondary results are not reported in the registry record. The posted primary result is the A1c mean at 8 months post-baseline. The record does not state which outcome was treated as primary in the original statistical plan beyond the posted primary outcome, how other outcomes were prioritized, or whether any adjustment for multiple comparisons was planned or performed.

Multiplicity arises when several outcomes, time points, or comparisons are examined. In general, considering many possible results can increase the chance that at least one appears unusually strong by chance. Methods for controlling that risk depend on the intended questions and analysis plan. Because the registry does not report such a plan or secondary results, it is not possible to assess how multiplicity was handled. The unadjusted p-value of 0.948 should not be described as adjusted for multiple testing.

The registry states that 37 participants had A1c data at final follow-up, with 17 in the PREP-DC group and 20 in standard care. It does not report the reasons for missing follow-up measurements, whether missingness differed by group, or how missing outcomes were treated analytically. It also does not report whether participants were analyzed according to randomized assignment, whether any imputation was used, or whether sensitivity analyses examined alternative assumptions about missing data. These details matter because conclusions from observed measurements can depend on why data are absent.

The record does not report a full analysis population definition, protocol deviations, intervention adherence, or a participant flow description sufficient to explain the difference between registry enrollment, arm descriptions, and the endpoint-specific counts. The enrollment entry is 52, while each arm description states 50 planned participants; the registry does not reconcile these entries. The posted outcome counts should therefore be interpreted as the numbers contributing to the reported endpoint summaries, not as a full accounting of enrollment, completion, or all randomized participants.

Interim analyses, stopping rules, and the original sample-size justification are not reported in the registry record. Nor are the sponsor's statistical plan or a detailed analysis method. The absence of these details does not show that a particular method was or was not used; it limits what can be concluded about prespecification and analysis choices.

14. 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 5% reporting threshold.

The adverse-event record lists 26 participants at risk in the PREP-DC group and 26 in the standard-care group. It reports 0 serious adverse events in each group, 0 other adverse events in each group, and 0 deaths in each group. The registry lists no serious adverse-event terms. These are the posted counts for the adverse-event categories and groups shown in the record.

A count of zero means that no event in that category was reported for the listed group in this registry entry. It does not prove that an event is impossible, nor does it establish that the intervention has no risks. Interpretation also depends on how events were defined, collected, and monitored, as well as how long participants were followed. Those details are not reported in the registry record. The adverse-event at-risk counts are not the same as the endpoint-specific A1c counts, and they should not be substituted for the A1c analysis population.

The registry results support only a descriptive statement about the reported event counts. They do not establish comparative safety or explain whether any events occurred outside the categories shown. No medical advice should be inferred from these registry counts.

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

The posted primary result describes A1c among participants with measurements at final follow-up. The PREP-DC mean was 7.988 and the standard-care mean was 8.025 at 8 months post-baseline. The estimated mean difference was -0.037 A1c percentage points. The interval from -1.154 to 1.08 shows that the estimate is imprecise and compatible with differences in either direction. The p-value of 0.948 is part of the unadjusted comparison, but it does not prove that the groups are equivalent or that the true difference is zero.

The result does not establish whether PREP-DC changes A1c relative to baseline, because baseline comparisons or change estimates are not reported in the registry record. It does not show the effect of the intervention on communication quality, clinic engagement, depressive symptoms, glucose monitoring frequency, or other measures mentioned in the study summary; secondary results are not reported in the registry record. Nor can the posted summary identify whether any observed contrast arose from intervention content, participant characteristics, missing data, or other factors.

The randomized design provides a framework for comparing assigned conditions, but a design label alone does not reveal the details of allocation, masking, adherence, or analysis. The registry does not report the primary analysis population or a detailed statistical plan. The available endpoint counts represent participants with final-follow-up A1c data, and the record does not explain why other participants lack those data.

Accordingly, the result is best understood as a low-precision estimate of the observed group-mean contrast, not as a definitive test that the intervention succeeds or fails. It does not support a claim of benefit, harm, or equivalence. It also does not settle the broader question of whether communication-focused transition support can affect outcomes beyond the posted endpoint.

16. Why This Trial Matters Statistically

This trial is statistically informative as an example of the difference between a point estimate and the precision of that estimate. The A1c means are close, and the estimated mean difference is -0.037. Considered alone, that point estimate might appear to suggest little separation between groups. The reported interval, however, extends from -1.154 to 1.08. It makes clear that the estimate is uncertain and that the data do not pin down the direction or size of a population difference.

The endpoint-specific counts and standard deviations are also important context. The PREP-DC mean is based on 17 participants and the standard-care mean on 20, with standard deviations of 1.996 and 1.345. A mean difference can be estimated, but limited outcome information combined with variation in individual measurements can leave considerable uncertainty. This is why the interval is central to interpretation rather than an optional detail alongside the means and p-value.

The study addresses a transition period that the registry describes as involving changes in self-care and preparation for adult diabetes care. Its intervention focuses on communication and readiness, while the posted primary outcome is A1c. That distinction matters: a clinical measure can be relevant to the rationale without capturing every intended skill or experience. The absence of secondary results means the broader aims cannot be evaluated from the posted outcome entry.

Finally, the planning illustration shows how strongly sample-size calculations depend on the assumed effect to detect. Using the observed effect yields large per-arm planning figures, and planning for smaller effects requires more participants under the stated assumptions. Those figures are not the study's original design plan and do not describe observed power. Keeping planning exercises distinct from trial results helps avoid treating a post hoc illustration as evidence about the design or the trial's ability to detect its actual effects.

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 primary result is based on final-follow-up A1c data for 37 participants, with 17 in PREP-DC and 20 in standard care. The registry does not report the reasons for missing outcome data, whether missingness was related to group or outcome, or whether missing-data methods were used. Without that information, the extent to which the observed summaries represent the randomized groups cannot be evaluated from the registry record.

The reported mean difference is unadjusted, and the registry does not give a detailed statistical method, confidence-interval level, or analysis plan. Baseline A1c results are not reported in the posted primary outcome, so it is not possible to assess baseline balance or interpret the result as a comparison of changes. The registry also does not report intervention adherence, treatment exposure, or a full analysis population definition.

There is a difference between the enrollment entry of 52 and the arm descriptions, which state that 50 participants would be randomized to each condition. The registry does not explain how these entries relate to one another. They should not be combined into an inferred account of randomization or completion. The outcome-specific counts are reported separately and are not a complete participant-flow explanation.

Secondary outcome results, multiplicity handling, interim analyses, stopping rules, and the original sample-size justification are not reported in the registry record. These omissions limit assessment of the broader study aims and of how the primary result fits within the full analysis plan. The adverse-event counts are descriptive; definitions, collection procedures, and monitoring details are not reported. The posted results therefore support a focused description of the final-follow-up A1c summaries, but not a comprehensive evaluation of all outcomes, analysis choices, or safety procedures.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Improving Health Communication During the Transition From Pediatric to Adult Diabetes Care — NCT03734107.
• Registry record last updated 2026-05-26; status last verified 2026-05.
• Results first posted 2026-05-05.
• 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

The registry describes a completed, randomized, parallel-group study with single masking of PREP-DC versus standard care for adolescents and young adults with type 1 diabetes preparing to transition to adult care. Enrollment is listed as 52, and the primary endpoint is mean hemoglobin A1c at 8 months post-baseline.

Final-follow-up A1c data were reported for 37 participants. The mean was 7.988 for PREP-DC and 8.025 for standard care; the posted mean difference was -0.037, with an interval from -1.154 to 1.08 and an unadjusted p-value of 0.948. The interval indicates substantial uncertainty about the direction and size of the contrast. Secondary results and key details of the sponsor's analysis plan are not reported in the registry record.