Effects of Exenatide on Overweight Adolescents With Prader-Willi Syndrome: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Effects of Exenatide on Overweight Adolescents With Prader-Willi Syndrome (NCT01444898), a na na study. The primary outcome is Change in Weight.

2. Clinical Question

3. Trial Design

This completed study, titled Effects of Exenatide on Overweight Adolescents With Prader-Willi Syndrome, was sponsored by Children's Hospital Los Angeles. The registry lists a start date of 2012-03 and a primary completion date of 2013-05. Enrollment was 10. The study phase is listed as NA.

The design is recorded as single-group, and allocation is listed as NA. The intervention description says that all enrolled participants received exenatide for 6 months. Masking is recorded as NONE. These design features mean the study follows outcomes in a treated group, rather than assigning participants to exenatide and a concurrent comparison group. The registry record does not describe a randomized allocation process or a blinded assessment procedure.

The population of interest is overweight adolescents with Prader-Willi Syndrome. The registry's summary gives background on appetite and obesity in this condition and describes the study's intended focus on weight, body composition, subjective appetite measures, and appetite-associated hormones. Detailed eligibility rules, recruitment methods, treatment adherence, and participant flow are not reported in the registry record. Nor are the actual dosing details complete in the record excerpt.

A single-group design can document what was observed over the follow-up period among enrolled participants. It cannot, by itself, separate a treatment-related change from changes that might have occurred over time for other reasons. The registry record does not report a comparison group, a statistical analysis plan, or numerical results for the primary endpoint. The completed status indicates the study is marked complete; it does not establish that all planned observations were available or analyzed.

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 Change in Weight, measured over 6 months.

The primary endpoint is change in weight, expressed in kg, after 6 months of treatment with the study drug. The registry specifies that the result is described as a mean with standard deviation. Weight is a continuous measurement, so a mean change can convey the average direction and magnitude of change in the analyzed group, while the standard deviation describes how dispersed individual change values are around that average.

In general, change from baseline is used to describe how a measurement differs between an initial assessment and a later assessment. Interpreting such a change requires knowing which participants contributed measurements at both assessments and how missing measurements were handled. Those analysis details are not reported in the registry record. The record also does not report the numerical mean change or standard deviation, nor a confidence interval or p-value for the primary endpoint.

Weight is one of several intended areas of assessment described in the study summary. The summary also refers to body composition, subjective measures of appetite, and appetite-associated hormones. The primary endpoint, however, is specifically the change in weight at 6 months. The reason for selecting weight as the primary endpoint is not reported in the registry record, so no additional rationale for that choice can be attributed to the investigators.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a mean change describe?

In general, a mean is the arithmetic average of measured values. For a change endpoint, each participant's change is ordinarily formed by comparing a later measurement with an earlier measurement, and the mean summarizes those changes across the analyzed participants. The registry defines the primary outcome as change in weight after 6 months and says it is described as a mean with standard deviation. It does not give the observed mean or standard deviation, or explain the specific calculation and analysis population used.

The standard deviation describes the spread of individual measurements around the mean. It is not the same as a confidence interval: the standard deviation characterizes observed variability among participants, whereas a confidence interval expresses uncertainty about an estimated quantity. In general, a confidence interval is affected by both variability and the amount of information available. No confidence interval for the primary endpoint is reported in the registry record, so its precision cannot be evaluated from that record.

What can a single-group design estimate?

In general, a single-group study can describe changes observed among participants who receive the intervention. It does not directly estimate the difference between outcomes under the intervention and outcomes under a concurrent alternative. The present record lists a single-group model, no masking, and allocation as NA; it does not describe a comparator group. Thus, even a complete before-and-after result would be a within-group observation, not a randomized between-group treatment effect.

Without a concurrent comparison, interpretation is vulnerable to influences that change over time, such as natural variation, concurrent care, or measurement circumstances. These are general limitations of single-group comparisons, not claims that any particular influence occurred in this study. The study record does not provide evidence to separate those possibilities from an intervention-related change.

What does statistical significance tell a reader?

In general, a p-value evaluates how compatible observed data are with a specified statistical model and null hypothesis. It does not measure the size or clinical importance of an effect, and it does not establish causation. A confidence interval presents a range of values compatible with the data and model at its stated confidence level; a narrow interval generally indicates greater precision than a wide interval. The registry record does not report a primary-endpoint p-value, confidence interval, or numerical estimate. It also does not report the statistical test or model used for that endpoint. No significance claim can therefore be assessed from the record.

Why does the analysis population matter?

In general, an analysis population specifies which participants' measurements contribute to a result. The number enrolled does not necessarily tell readers how many had usable outcome data at follow-up. A change analysis may require measurements at more than one time point, and missing values can affect both the estimate and its uncertainty. The analysis population, participant flow, and approach to missing measurements are not reported in the registry record. It is therefore unclear whether the primary analysis included all enrolled participants or a subset.

What do planning calculations mean?

The registry's sample-size assumptions describe planning illustrations based on an observed effect, not the trial's own design. They use a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect to detect expressed as a fraction of the observed effect. The record specifies that time-to-event calculations use total events and other calculations use participants per arm. Those illustrations are not observed power and do not establish that the single-group study was designed for a particular detectable effect. A two-arm planning setup also does not change the recorded study design: this trial is listed as single-group and has no like-for-like control comparison.

In general, power is a design-stage probability of detecting a specified effect under stated assumptions. It is not a measure of whether a result is true, and calculating power after observing results does not resolve uncertainty in the estimate. No numerical sample-size target or justification for this study's enrollment is reported in the registry record. The planning illustrations should therefore be read as hypothetical calculations rather than as evidence about the strength of the observed findings.

Why can outcome variability matter?

For continuous outcomes, a mean can conceal differences in individual responses. The standard deviation helps describe dispersion, but the registry does not report it for the primary result. In general, unusually dispersed values can make an average less representative of any particular participant and can increase uncertainty in an estimated mean. Statistical methods may need to account for features such as skewed distributions or unusually variable data; the method used is not reported in the registry record.

The endpoint is weight change, but no distributional information, diagnostic checks, or sensitivity analyses are reported. It is therefore not possible to assess whether the statistical method matched the observed data or whether alternative methods would have changed the estimate. This distinction is especially relevant when interpreting a small enrolled group: a summary average may be sensitive to the values of individual participants. No additional numerical calculations are warranted from the registry information available.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Exenatide")
n   <- c(10)
m   <- c(-0.5)
sp  <- c(0.9)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Exenatide  10  -0.500  0.900  -1.144  0.144

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 9 outcome measures and 9 analyses. The study summary describes interest in weight, body composition, subjective appetite measures, and appetite-associated hormones, while the designated primary endpoint is change in weight after 6 months. The record does not report how the other outcomes were ranked, whether any formed a formal secondary-outcome hierarchy, or whether statistical testing was adjusted for multiple outcomes. A multiplicity plan is therefore not reported in the registry record.

In general, testing many outcomes can increase the chance that at least one result appears noteworthy by chance. Prespecifying a primary endpoint and a testing strategy helps readers distinguish the main question from exploratory analyses. Here, the primary endpoint is identified, but the analysis strategy and any adjustment procedures are not reported. The list of outcome and analysis counts alone does not establish which results were confirmatory or how they should be interpreted together.

Missing-data methods and analysis populations are also not reported in the registry record. The enrollment count does not establish how many participants contributed complete weight measurements at 6 months. The record does not state whether missing observations occurred, how any were handled, or whether sensitivity analyses were conducted. The primary endpoint's population field is blank.

Interim analyses, stopping rules, and a detailed statistical analysis plan are not reported in the registry record. Their absence from the record should not be interpreted as proof that none existed; their status cannot be determined from the information recorded. These gaps limit assessment of whether the analyses followed a prespecified plan and how robust the results are to missingness or multiple testing.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

Most frequent non-serious adverse event terms

The registry records 0 serious adverse events among 10 participants at risk in the exenatide group. It records other adverse events affecting 2 of 10 participants at risk. These are participant counts as categorized in the registry; they do not describe event severity beyond the serious-versus-other categorization or establish a cause.

The deaths field is null, so a death count is not reported in the registry record; null should not be read as a confirmed count of zero. The registry does not list serious adverse event terms. It also does not provide event descriptions for the other adverse events, their timing, duration, outcome, or attribution. The observation period and any detailed safety analysis methods are not reported.

In general, a small group and a limited record of event details provide a narrow description of observed safety events. A count of zero recorded serious events does not establish that an event cannot occur, and counts alone do not support comparison with another treatment when no comparator is described. These registry figures should be read as recorded events among the listed participants, not as a complete characterization of safety.

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

The study addresses a specific question in overweight adolescents with Prader-Willi Syndrome: what happens to weight over 6 months of exenatide treatment in a single group? The registry defines change in weight as the primary endpoint and reports enrollment of 10. However, the mean change and standard deviation are not reported in the registry record. The record therefore does not establish the observed direction or size of weight change, nor how precisely it was estimated.

The design also limits what could be inferred even if the numerical result were available. With no separate control group described, an observed change would not distinguish the effect of treatment from other changes over time. A single-group study can contribute descriptive evidence about the participants followed, but it does not provide a randomized comparison of exenatide with an alternative.

The registry's study summary describes intended assessment of body composition, appetite, and appetite-associated hormones in addition to weight. The available record does not provide numerical results for those outcomes either. A mechanistic rationale or a stated hypothesis is not a substitute for outcome data. The record's explanation of why the investigators were interested in exenatide does not establish that the hypothesized changes occurred.

The serious adverse event count is recorded as 0 among 10 at risk, while other adverse events are recorded for 2 of 10. Those counts are limited to the registry's categories and do not by themselves establish cause, comparative safety, or the absence of unrecorded events. The death count is not reported in the registry record.

Accordingly, the record supports a description of the study question, design, enrollment, and listed adverse-event counts, but not a quantitative conclusion about the primary outcome. It does not show that exenatide did or did not change weight. Such a conclusion would require numerical outcome results and, for a causal treatment comparison, an appropriate comparator design.

14. Why This Trial Matters Statistically

This study is statistically instructive because its clinical question and primary endpoint are identifiable, while the design and available results constrain interpretation. The endpoint is change in weight after 6 months, summarized as a mean and standard deviation. Yet the numerical estimate and its uncertainty are not reported in the registry record. This illustrates why naming an outcome is not enough to evaluate a result: readers also need the estimate, its variability or uncertainty, and a clear account of who contributed data.

The single-group design makes the distinction between describing change and estimating a treatment effect especially important. A before-and-after observation can describe what happened in the enrolled group. Without a concurrent comparator, it cannot establish how those same participants would have fared under another condition. This distinction is central to clinical biostatistics because design determines the comparison that an analysis can support.

The record also lists multiple outcomes and analyses, while not reporting a multiplicity plan, missing-data methods, or detailed statistical methods. These omissions matter because readers need to know how the primary result was selected and analyzed, how incomplete observations were handled, and how secondary findings were interpreted. The counts of outcomes and analyses do not answer those questions.

Finally, planning illustrations based on an observed effect should not be confused with the original design or with observed power. Their assumptions describe hypothetical two-arm calculations, while the registered study is single-group. Keeping those concepts separate helps prevent a planning calculation from being mistaken for evidence about the precision or strength of this study's findings.

15. 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 direct limitation is that the primary numerical result is not reported in the registry record. The mean change in weight and its standard deviation are absent, as are a confidence interval and p-value. Readers cannot quantify the observed change or assess its precision. Numerical results for the other outcomes described in the study summary are also not reported in the record.

The design is single-group, with allocation listed as NA and no separate comparator described. Any observed change over time would therefore lack a concurrent reference for changes that might have occurred without the intervention. This limits causal interpretation. The study is also small in enrollment, with 10 participants, so individual observations could materially affect a group summary; the actual analyzed count is not reported.

Several reporting details needed to assess the endpoint are absent. The analysis population, participant flow, handling of missing measurements, statistical test or model, and any sensitivity analyses are not reported in the registry record. The population field for the primary outcome is blank. Eligibility definitions and detailed dosing instructions are also incomplete in the record excerpt, limiting assessment of who was included and precisely how treatment was delivered.

The record lists 9 outcome measures and 9 analyses but does not report a multiplicity strategy or detailed statistical analysis plan. Interim analyses and stopping rules are not reported. Safety reporting is limited: serious adverse event terms are not listed, descriptions of other adverse events are absent, and the deaths field is null rather than a reported count. These limitations constrain both interpretation of outcomes and assessment of how completely the trial is represented in the registry record.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Effects of Exenatide on Overweight Adolescents With Prader-Willi Syndrome — NCT01444898.
• Registry record last updated 2016-09-29; status last verified 2016-09.
• Results first posted 2016-09-29.
• 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.

19. Record Summary

This completed study evaluated exenatide in overweight adolescents with Prader-Willi Syndrome. It was sponsored by Children's Hospital Los Angeles, had enrollment of 10, and is recorded as a single-group study with no masking. The registry lists a start date of 2012-03 and a primary completion date of 2013-05. Participants in the intervention group were described as receiving exenatide for 6 months.

The primary endpoint was change in weight in kg after 6 months, described as a mean with standard deviation. The numerical primary result, its variability, and inferential statistics are not reported in the registry record. The record also lists 9 outcome measures and 9 analyses, without reporting a multiplicity plan, missing-data approach, or detailed statistical analysis plan.

The registry records 0 serious adverse events among 10 at risk and other adverse events affecting 2 of 10. A death count is not reported in the registry record. Because the study has no separate comparator and the primary numerical result is unavailable, the record does not support a quantitative conclusion about treatment-related change in weight.