Unacylated Ghrelin to Improve Functioning in PAD: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Unacylated Ghrelin to Improve Functioning in PAD (NCT04377126), a randomized phase 2 study. The primary outcome is 4-month Change in Six-minute Walk Distance.

2. Clinical Question

3. Trial Design

GIFT is registered as a Phase II, randomized, double-blinded, parallel-group trial of unacylated ghrelin and placebo in peripheral artery disease. The study status is completed. The registry dates are 2020-07-08 for the start and 2025-01-23 for primary completion. The enrollment field records 25; the brief summary separately describes a plan to randomize 30 participants. These figures refer to different record entries and should not be treated as interchangeable.

The intervention descriptions specify daily self-administration by subcutaneous injection for four months. Participants assigned to unacylated ghrelin were to receive 20 ug/kg daily. The placebo was an identical-appearing bacteriostatic saline solution. The description says syringes were not labeled with the group assignment, consistent with the recorded double-blinded design. The registry does not report further details about who was blinded or how random assignment was generated or concealed.

The primary outcome was change in six-minute walk distance between baseline and four-month follow-up, measured in meters. Secondary outcomes listed in the record include four-month change in maximal treadmill walking time and four-month change in calf muscle perfusion. The record lists five outcome measures and five analyses, but only two secondary outcomes as posted. It does not report the full outcome-measure list or explain the difference in reporting coverage.

The primary outcome analysis excluded one participant in the unacylated ghrelin group because the four-month follow-up walk test was missing. The registry does not report the original statistical plan, the intended analysis population, methods for handling missing outcomes, or whether the posted analysis followed a prespecified protocol. The sponsor is Northwestern University.

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

Analysis population for the primary outcome, as defined in the registry: One participant in the Unacylated ghrelin group was missing FV4 six-minute walk test and was excluded from this analysis.

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 4-month Change in Six-minute Walk Distance, measured over Baseline to 4 months.

The primary endpoint is change in six-minute walk distance from baseline to four-month follow-up. The six-minute walk test measures the distance a participant can walk during a fixed period. As a continuous measure, it retains information about the amount of change rather than reducing the result to categories such as improved or not improved. The registry records the endpoint unit as meters and describes the reported parameter as a least-squares mean.

Walking distance is relevant to the trial’s stated focus on functioning in people with peripheral artery disease. Comparing change between randomized groups is intended to distinguish the outcome pattern associated with assignment to unacylated ghrelin from the pattern under placebo. The posted description says the comparison is between baseline and four-month follow-up, and the brief summary identifies this as the primary outcome.

The endpoint is not a direct measure of every aspect of functioning, blood flow, muscle growth, or energy use. Those ideas appear as background rationale in the brief summary, not as the primary endpoint itself. The record also lists maximal treadmill walking time and calf muscle perfusion as secondary outcomes. The six-minute walk result should therefore be interpreted specifically as a group comparison in change in walking distance, not as a complete account of all possible effects or outcomes.

7. Results Posted in the Registry

• Unacylated Ghrelin: mean -17.13 versus 23.06 on control; difference -40.19 (95% CI -82.57 to 2.19), standardized effect d = -0.77; z-test p = 0.063.

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes the primary measure as continuous and reports least-squares means with standard errors. A continuous outcome can take a range of values, such as walking distance in meters. A mean summarizes the average value or change in a group. A least-squares mean is a model-based mean; the registry does not give enough detail to determine precisely how the sponsor’s model produced it or what, if any, adjustments it included. The record’s brief endpoint description focuses on change from baseline, while the sponsor analysis is labeled as a comparison of final values. That distinction matters when interpreting what the reported model estimates.

What does a standard error describe?

A standard error describes the statistical uncertainty around an estimated quantity, such as a group mean. It is not the same as the spread of individual participant outcomes. A smaller standard error generally indicates a more precisely estimated mean, while a larger standard error indicates greater uncertainty. The posted group estimates have standard errors of 17.24 meters for unacylated ghrelin and 13.05 meters for placebo. Those values help convey the uncertainty in each group estimate but do not show the full range of individual walking changes.

What does the mean difference represent?

A mean difference expresses the contrast between group means in the outcome’s units. In the simple re-calculation, the estimated difference is -40.19 meters, with the comparison defined as unacylated ghrelin relative to placebo. The negative sign indicates that the estimated change in the ghrelin group is lower than the estimated change in the placebo group. The same numerical estimate appears in the sponsor’s reported analysis, but the associated inferential results differ. A matching point estimate does not make confidence intervals or p-values interchangeable: they may depend on the analysis method and assumptions.

How should the confidence interval be understood?

A confidence interval is a range of values compatible with the observed data and the method used to calculate it. In general, a narrower interval indicates greater precision, and a wider interval indicates less precision. The simple recalculation gives a 95% interval from -82.57 to 2.189 meters. This interval spans zero, so the recalculated summary does not pin down the direction of the underlying difference with high precision. The sponsor report gives a 90% confidence level and a lower bound of -68.23, but does not report an upper bound. The two intervals differ in confidence level as well as in the reported analysis, and the missing upper bound prevents a full comparison of their ranges.

What does a p-value address?

A p-value describes how unusual the observed data, or more extreme data, would be under a specified null model and its assumptions. It is not the probability that the null hypothesis is true, nor does it measure the size or importance of an effect. The unadjusted re-calculated p-value is 0.063; the sponsor-reported p-value is 0.964. These values come with the noted discrepancy, and the sponsor’s own analysis takes precedence. The registry does not report enough methodological detail to identify why the p-values differ or to verify the sponsor’s full analysis independently.

Why can over-dispersion matter?

General statistical context: over-dispersion occurs when outcome variability is greater than a model assumes. If a model understates variability, standard errors can be too small and inferential results can look more precise than warranted. This is a general consideration, not a reported feature of the GIFT analysis. The outcome is continuous, and the record does not say that an over-dispersion model was used or that over-dispersion was assessed. It would therefore be inappropriate to attribute the observed discrepancy to over-dispersion.

What can be reconstructed from summary statistics?

The recalculated comparison is an unadjusted calculation based on the posted group summaries. It is useful as a transparent check of the reported group estimates, but it does not reproduce every possible model-based analysis. The calculation uses the group means, standard errors, and sample sizes recorded for the outcome; the pooled standard deviation is marked as approximate. The registry does not report enough information about the sponsor’s model, its covariance assumptions, or its handling of baseline and missing data to reconstruct that model. Because the record explicitly flags a discrepancy, the recalculation should be read as a separate descriptive statistical check, not as a substitute for the sponsor’s reported analysis.

In general, randomized assignment supports a group comparison by reducing systematic differences at the start of a trial on average, but randomization does not guarantee identical groups in a small study. Nor does it resolve missing outcome data or discrepancies in analysis. The record confirms randomized allocation and double masking, but does not report the randomization procedure, concealment details, balance of baseline characteristics, or a complete analysis plan. Those methods should not be inferred from the design labels alone.

10. Confidence Intervals and Precision

The precision of the primary estimate is limited by the width and completeness of the reported uncertainty summaries. The simple unadjusted re-calculation gives a mean difference of -40.19 meters, with a 95% confidence interval from -82.57 to 2.189. This range includes zero and covers both negative and positive differences. It therefore leaves considerable uncertainty about the direction and size of the group contrast under that calculation. It should not be read as a range of individual participant outcomes.

The group-level standard errors are 17.24 meters for unacylated ghrelin and 13.05 meters for placebo. These describe uncertainty in the estimated group means, not the variability among all participants. The reported group sample sizes are 11 and 13. One participant in the ghrelin group was missing the four-month six-minute walk test and was excluded from the primary analysis. The record does not give an imputation approach or sensitivity analysis for this missing result.

The sponsor’s analysis reports a 90% confidence level, an estimate of -40.19, and a lower bound of -68.23, but no upper bound. Since the upper bound is absent, the complete sponsor-reported interval cannot be assessed. Also, the sponsor’s reported p-value of 0.964 differs from the unadjusted recalculated p-value of 0.063. The registry flags the discrepancy, and the sponsor’s own analysis takes precedence. Without a full interval and a fuller model description, the sponsor estimate’s precision cannot be characterized completely from the record.

Confidence intervals communicate uncertainty under their analysis assumptions; they do not account automatically for missing data, selective reporting, or uncertainty about which analysis is appropriate. The registry does not report enough information to evaluate those issues fully.

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 planning figures are illustrations based on the observed effect, not the trial’s original design calculation. They assume a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect used for each illustration is the stated fraction of the observed effect. The trial’s own original sample-size assumptions are not reported in the registry record.

For planning based on 100% of the observed effect, the illustration gives 27 participants per arm for 80% power and 36 participants per arm for 90% power. For planning for 75% of the observed effect, the corresponding figures are 47 participants per arm for 80% power and 63 participants per arm for 90% power. For planning for 50% of the observed effect, the figures are 105 participants per arm for 80% power and 141 participants per arm for 90% power. These are participants per arm, not total event counts.

In general, a power target describes the chance that a planned study would detect an effect of the specified size under the assumed statistical model and conditions. The 80% column gives the planned number per arm for an 80% power target; the 90% column gives the planned number per arm for a 90% target. Higher planned power requires more participants for a given assumed effect. Smaller effects need more participants to detect than larger effects, which is why the illustration’s participant requirement rises as the assumed fraction of the observed effect falls.

These estimates are not observed power. They are not a retrospective measure of whether the completed trial was adequately powered, and they should not be interpreted as evidence about the observed result’s reliability. Because they are derived from the observed effect, they may be especially sensitive to uncertainty in that estimate. The discrepancy between the simple recalculation and the sponsor analysis is also relevant context when considering an effect-based planning illustration.

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 = -40.190; pooled standard deviation σ = 51.901.
2. n = 2 × (1.96 + 0.842)² × 51.901² / -40.190² = 26.2, rounded up to 27 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 <- -40.19                      # observed difference in means
sigma <- 51.9007470606594                     # 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(4377126)
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 = 27 (80% power), 36 (90% power)
 75% of observed effect: n per arm = 47 (80% power), 63 (90% power)
 50% of observed effect: n per arm = 105 (80% power), 141 (90% power)
power.t.test: 27.2 
Simulated power at n = 27 per arm: 0.795 (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. Analyses Reported by the Sponsor

The sponsor’s reported analysis is identified as ANOVA and as a comparison of final values. It reports a mean difference of -40.19, a 90% confidence level, a lower confidence bound of -68.23, no upper confidence bound, and p = 0.964. The record does not report further details of the model or explain the missing upper bound.

A simple unadjusted re-calculation using the posted group summary statistics gives the same point estimate, -40.19, but a 95% confidence interval from -82.57 to 2.189 and p = 0.063. These are not interchangeable analyses: the re-calculation is a separate, unadjusted check, while the sponsor analysis is the trial’s own reported analysis. The registry explicitly flags the discrepancy. In keeping with that record, the sponsor’s own analysis takes precedence over the recalculation for interpretation of the trial’s reported inferential result.

The available information does not establish the reason for the difference. It could not be resolved by assuming an adjustment, a different analysis population, or a particular model specification, because those details are not reported. The prudent reading is to state both sets of results, identify their different sources and confidence levels, and avoid presenting the recalculation as the sponsor’s finding.

14. Multiplicity, Missing Data and Analysis Populations

The registry lists five outcome measures and five analyses, while two secondary outcomes are posted: four-month change in maximal treadmill walking time and four-month change in calf muscle perfusion. The primary endpoint is four-month change in six-minute walk distance. The record does not report a multiplicity adjustment, a hierarchy among outcomes, or a detailed prespecified testing strategy. It is therefore not possible to determine whether or how the analyses accounted for the possibility of false-positive findings when testing multiple outcomes. The registry entries do not include results for the secondary outcomes, so their findings cannot be used to assess consistency with the primary endpoint.

For the primary outcome, one participant in the unacylated ghrelin group was missing the four-month six-minute walk test and was excluded from the analysis. The registry does not report why the test was missing, whether the participant’s baseline measurement was available, or whether any missing-data method or sensitivity analysis was applied. It also does not describe missingness in the placebo group or for the secondary outcomes. No assumptions about the cause or consequences of missing data can be made from the record.

The intended analysis population is not reported in the registry record. The available description identifies the participant excluded from the primary analysis but does not say whether the analysis was intention-to-treat, per-protocol, or based on another population definition. Nor does it provide the full protocol or statistical analysis plan. The sponsor analysis is labeled ANOVA, but its full model specification, adjustments, and handling of the baseline measurement are not reported.

These omissions matter because decisions about which outcomes to test, which participants to include, and how to handle missing measurements can affect interpretation. They do not demonstrate that the analysis was inappropriate; they mean that the registry information is insufficient to evaluate those decisions. The discrepancy between sponsor and recalculated results adds a further reason to keep the reported analysis and the unadjusted check distinct.

15. Safety Results

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

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: acute coronary syndrome (8.3%), coronary revascularization (8.3%), colon cancer surgery (8.3%), leukocytosis (7.7%), gastroenteritis (7.7%).

The adverse-event record reports serious adverse events affecting 2 of 12 participants at risk in the unacylated ghrelin group and 3 of 13 participants at risk in the placebo group. Other adverse events affected 5 of 12 at risk in the unacylated ghrelin group and 9 of 13 at risk in the placebo group. The record reports zero deaths in each group. These figures describe the posted counts and denominators; they do not establish that an event was caused by the assigned intervention.

The record also lists serious-event terms with percentages: acute coronary syndrome, coronary revascularization, and colon cancer surgery at 8.3% each; leukocytosis, gastroenteritis, and stroke at 7.7% each. These term-level percentages are not accompanied by additional counts or a fuller explanation of their presentation in the registry record. They should not be assigned to one treatment group without further information.

Safety comparisons can be difficult to interpret in a small trial, particularly when event types vary and the record provides limited detail on timing, duration, severity, relatedness, or participant-level overlap. The adverse-event entries are descriptive registry information, not a statistical test of differences between groups. The registry record does not report enough detail to draw a broader comparative safety conclusion from these counts alone.

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

The posted primary outcome estimates show different average changes in six-minute walk distance across the randomized groups: -17.13 meters for unacylated ghrelin and 23.06 meters for placebo. The simple unadjusted mean difference is -40.19 meters, with a recalculated 95% confidence interval from -82.57 to 2.189 and p = 0.063. The sponsor’s own analysis reports the same point estimate but a p-value of 0.964 and an incomplete 90% confidence interval. Because the record flags a discrepancy, the sponsor’s analysis takes precedence; the recalculation is a separate statistical check.

These results describe the posted data and the analyses recorded, not a definitive account of treatment effect. The interval from the recalculation is broad and includes zero, and the sponsor’s uncertainty summary is incomplete. The record does not provide an explanation for the difference in inferential results. It also does not provide the full analysis plan, details of model adjustment, or results for the listed secondary outcomes. Those gaps constrain what can be concluded about the trial as a whole.

The trial was registered as a Phase II study and the brief summary characterizes it as a pilot. Its record lists enrollment of 25, while the brief summary states a plan to randomize 30. The primary analysis excluded one participant from the ghrelin group because the follow-up walk test was missing. The registry does not report the implications of that missing result or a sensitivity analysis.

The primary endpoint captures walking distance over a six-minute test, not every aspect of PAD or functioning. Results on this endpoint alone cannot establish effects on calf muscle perfusion, maximal treadmill walking time, or other outcomes. Nor do the posted figures establish clinical importance: the registry does not provide a threshold for meaningful change. The result should be understood as an uncertain group comparison in a specific endpoint and follow-up period, with a material discrepancy between the reported sponsor analysis and an unadjusted recalculation.

17. Why This Trial Matters Statistically

This trial is statistically instructive because its record brings together randomized design, a continuous functional outcome, uncertainty in a small study, missing outcome data, and a discrepancy between a sponsor analysis and a simple recalculation. Those features show why a point estimate alone is not enough to understand a trial result. The same estimated mean difference can be accompanied by substantially different inferential summaries, and readers need to know which result comes from the trial’s own analysis.

The distinction between the sponsor analysis and recalculation is especially important. The unadjusted calculation is transparent and can serve as a check on the posted group summaries, but it is not a substitute for the sponsor’s model-based analysis. The registry explicitly flags a discrepancy, so the sponsor result takes precedence. At the same time, the record does not explain the discrepancy or provide enough model detail to resolve it independently. Careful reporting preserves that uncertainty rather than choosing whichever p-value seems more intuitive.

The missing four-month walk test also matters methodologically. Excluding a participant is a factual part of the primary analysis, but the record does not explain the reason for missingness or report a sensitivity analysis. Missing-data assumptions can influence how representative an analysis is of the randomized groups. The information available does not support a judgment about the direction or size of any such influence.

Finally, the planning illustrations emphasize that sample-size requirements depend on the effect assumed for planning and on the desired power. They are not observed power and do not reveal the study’s original design rationale. The original sample-size assumptions are not reported in the registry record. Taken together, these points underscore the value of transparent analysis methods, complete uncertainty reporting, and clear descriptions of outcome and missing-data handling.

18. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The registry record does not provide the full protocol or statistical analysis plan. It therefore does not establish the original sample-size justification, the precise randomization procedure, allocation concealment, the sponsor model’s full specification, or whether the primary analysis was adjusted for baseline values. The trial is marked randomized and double-blinded, but those labels alone do not fill in these methodological details.

The reported sponsor analysis has an incomplete confidence interval: a lower bound is present, but an upper bound is not reported. Its p-value also differs from the unadjusted recalculated p-value, and the record flags this discrepancy without explaining it. The recalculated standard deviation is marked approximate, and the calculation is unadjusted. These constraints make it unsuitable as a replacement for the sponsor analysis.

For the primary endpoint, one participant in the ghrelin group was excluded because the four-month walk test was missing. The record does not describe the missingness mechanism, imputation, or sensitivity analysis. It does not identify the intended analysis population or state whether other participants or outcome measurements were excluded. As a result, the effect of missing information on the reported comparison cannot be evaluated.

The brief summary describes a plan to randomize 30 participants, whereas the enrollment field records 25. The registry does not explain this difference. The available posted results also do not include the secondary outcome findings, despite listing two secondary outcomes and five analyses overall. No multiplicity procedure is reported. These omissions limit assessment of the full outcome pattern, analysis selection, and the original design assumptions.

Finally, the record supplies no threshold for interpreting the clinical importance of a change in walking distance. The primary result should therefore remain a statistical description of the posted measure and comparison, rather than a claim about clinical benefit or harm.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Unacylated Ghrelin to Improve Functioning in PAD — NCT04377126.
• Registry record last updated 2026-06-01; status last verified 2026-04.
• Results first posted 2026-06-01.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

22. Record Summary

NCT04377126, titled “Unacylated Ghrelin to Improve Functioning in PAD,” is a completed Phase II randomized, double-blinded, parallel-group trial sponsored by Northwestern University. The registry records a start date of 2020-07-08, primary completion on 2025-01-23, and enrollment of 25. The brief summary describes a plan to randomize 30 participants.

The primary endpoint was change in six-minute walk distance from baseline to four months. Posted group estimates were -17.13 meters for unacylated ghrelin and 23.06 meters for placebo. The sponsor’s reported analysis gives a mean difference of -40.19, p = 0.964, and an incomplete 90% confidence interval. A simple unadjusted recalculation gives a 95% confidence interval from -82.57 to 2.189 and p = 0.063. The record flags this discrepancy, so the sponsor’s analysis takes precedence.

One ghrelin-group participant missing the follow-up walk test was excluded from the primary analysis. The registry lists maximal treadmill walking time and calf muscle perfusion as secondary outcomes but does not report their results in the available record.