Implications for Treatment of the Metabolic Syndrome: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Implications for Treatment of the Metabolic Syndrome (NCT00666029), a randomized phase 2 study. The primary outcome is Muscle Microvascular Function.

2. Clinical Question

The question is focused on a physiological measure in volunteers with metabolic syndrome. The registry record does not report a broader clinical endpoint as the primary outcome, nor does it provide a posted secondary-outcome analysis that would extend the comparison to other outcomes. The interpretation therefore rests on the reported mean values, their variability, and the uncertainty in the comparison between arms. The question is whether the observed data distinguish the arms on this measure; the result alone does not establish what a difference would mean for a person's health.

3. Trial Design

The registry identifies the study as phase 2 and reports its status as completed. It lists a start date of 2006-02 and a primary completion date of 2008-02. The sponsor is University Hospital Southampton NHS Foundation Trust. The stated enrollment is 40. The brief summary describes both characterization of metabolic syndrome features in volunteers and a randomized trial intended to examine whether statin treatment improves muscle microvascular blood flow.

The record reports randomized allocation and double masking. It names atorvastatin and placebo as the interventions, and describes the active treatment as atorvastatin 40 mg once daily and the placebo as a dummy pill. The registry's design-model field is coded as single group, while the allocation field says randomized and the outcome data list separate atorvastatin and placebo arms. These entries do not align neatly. The record does not provide enough detail to resolve the design-model coding, so the trial should be described with that inconsistency in mind rather than assigning an unreported design structure.

The primary outcome is a continuous mean measure of skeletal muscle microvascular function, assessed at 6 months. The posted arm summaries include 17 participants for atorvastatin and 18 for placebo. The outcome description separately notes missing data on two participants in each arm. These reported analysis counts and missing-data notes are presented as recorded; the registry does not explain how the analysis population was defined or how missing values were handled.

The record lists two outcome measures, but only the primary endpoint is characterized in the posted results. It reports zero analyses and no posted secondary analyses. Details such as the randomization procedure, concealment, exact masking arrangements, treatment adherence, and the original statistical analysis plan are 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.

Overall Study

Analysis population for the primary outcome, as defined in the registry: There was missing data on two participants in the atorvastatin arm and two participants in the placebo arm.

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: Age 18-75 years, body mass index (BMI) 20-35 kg/m2, with \> 3 criteria for the metabolic syndrome. (One person in the placebo arm did not have complete baseline data).

6. Primary Endpoint

The registry lists the primary outcome as Muscle Microvascular Function, measured over 6 months.

The primary endpoint is titled Muscle Microvascular Function. It is a continuous measure reported as a mean with standard deviation at 6 months, in units of 10^3 mL*min^-1*100ml^-1*mmHg^-1. The registry describes skeletal muscle microvascular function measured with a Filtrass plethysmographic system, a passive inductive transducer, and a small pressure-step venous congestion protocol.

In the described procedure, limb volume change is measured while pressure steps are applied around the thigh. Fluid filtration rate is derived from the slope of limb-volume change during the final 2 minutes of each pressure step, then related to cuff pressure. The slope of that relationship above pressures associated with net filtration is used as a measure of Kf, or microvascular filtration capacity. The record explains that this capacity reflects exchange surface area and permeability. This physiological measure is used to characterize microvascular function, which is the biological feature the trial set out to examine.

The registry reports a coefficient of variation for the Kf measurement of 14.5%. This describes variability associated with the measurement procedure; it is not the treatment-effect estimate or the uncertainty interval for the difference between arms. The primary outcome is therefore a technical physiological endpoint, not a direct measure of symptoms, functional status, or a clinical event. The registry record does not report how changes in this measure relate to outcomes that matter to participants.

7. Results Posted in the Registry

• Atorvastatin: mean 3.70 versus 4.00 on control; difference -0.30 (95% CI -1.14 to 0.54), standardized effect d = -0.24; z-test p = 0.483.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary endpoint is continuous, so the registry reports a mean and standard deviation for each arm. A mean describes the central value of the observed measurements, while a standard deviation describes how spread out those measurements are around the mean. In this trial, the means were 3.7 for atorvastatin and 4.0 for placebo; the corresponding standard deviations were 1.4 and 1.1. These summaries give a basic description of each arm but do not, on their own, show how precisely the arms differ.

The reported mean difference is -0.3. The comparison information lists placebo as the reference value of 4.0 and atorvastatin as 3.7, so the negative sign corresponds to the atorvastatin mean being lower than the placebo mean. The difference is expressed on the scale of the endpoint. It is not a percentage change, and no percentage contrast is reported. A mean difference retains the measurement units and can be interpreted in relation to the clinical and measurement context, although the registry does not provide a threshold for a meaningful difference.

A confidence interval describes uncertainty around an estimated quantity under the statistical method used. For the mean difference, the reported interval runs from -1.137 to 0.537. Because the interval includes values on both sides of zero, it does not restrict the plausible direction of the contrast to one side. Its width also indicates that the estimate is not highly precise. A confidence interval is not a range containing a fixed proportion of individual participant measurements, and it is not a guarantee that the true effect falls inside that particular interval. The method used to calculate this interval is not reported in the registry record.

The unadjusted p-value is 0.483. In general, a p-value measures how surprising data at least as incompatible with a null hypothesis would be under that hypothesis and the assumptions of a statistical test. It does not give the probability that the treatment has no effect, nor does it convey the size or importance of the effect. The record does not identify the test used or specify whether the trial analysis included any covariate adjustment. The p-value should therefore be interpreted as the posted unadjusted comparison, rather than as a complete account of the analysis plan.

Over-dispersion is a concern when the variability in data exceeds what a chosen model assumes. In general, underestimating variability can make uncertainty appear smaller than it is, while accommodating extra variability can yield more realistic uncertainty. The endpoint is reported as a continuous measure with standard deviations, and the registry does not report an over-dispersion model or indicate that over-dispersion was assessed. This concept should not be mistaken for a finding about this trial.

The measurement description gives a coefficient of variation of 14.5% for Kf measurement. In general, a coefficient of variation expresses variability relative to the scale of a measurement and can help readers understand repeatability. It is distinct from the standard deviation of the trial-arm measurements and from the confidence interval for the treatment contrast. The registry does not describe the procedures used to estimate this coefficient or provide additional repeatability results.

Randomized allocation can, in general, support a comparison by balancing measured and unmeasured characteristics across groups on average. That general rationale does not establish that balance was achieved in this particular trial. The record says allocation was randomized and masking was double, but the randomization method, allocation concealment, baseline balance, and details of who was masked are not reported in the registry record. Its single-group model coding also sits uneasily alongside the randomized allocation and two separately reported arms, and the record does not explain the coding.

Sample-size calculations in the record are planning illustrations based on the observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The calculation considers detecting the stated fraction of the observed effect. In general, a smaller target effect is harder to distinguish from random variation and requires more participants for the same planned power. These calculations do not document the trial's original design assumptions; those are not reported in the registry record. The planning values are not observed power and should not be treated as a retrospective measure of whether the trial succeeded.

Finally, the number of analyses is listed as zero, and no secondary analyses are posted. The registry record does not provide a detailed statistical analysis plan, describe an interim analysis, or report multiplicity control. It is therefore not possible to determine from this record whether the posted comparison matches a prespecified analysis or how the investigators planned to handle multiple outcomes or repeated testing.

10. Confidence Intervals and Precision

The mean difference is -0.3, and its confidence interval extends from -1.137 to 0.537. The interval includes zero and values in both directions. It therefore does not identify a single direction of difference with precision. The data are compatible with a lower mean in the atorvastatin arm, little difference, or a higher mean, within the interval and under the method used to construct it.

The interval is also broad relative to the point estimate. This means the observed mean difference should not be read as an exact estimate of the underlying contrast. A confidence interval communicates sampling uncertainty; it does not describe the range of individual participants' measurements, and it does not account automatically for every potential source of bias or measurement error. The method used to calculate the interval is not reported in the registry record.

The arm-level standard deviations, 1.4 for atorvastatin and 1.1 for placebo, show variation among the observations within each arm. The outcome description separately notes missing data on two participants in each arm, and the posted arm counts are 17 and 18. The record does not explain the missing-data method or the population used for the comparison. Consequently, the interval's precision cannot be assessed independently of those analysis details.

The p-value of 0.483 complements the interval but answers a different question from the estimated effect. Neither statistic establishes that the arms are equivalent. The registry does not report a prespecified equivalence margin or a minimum clinically important difference, so the range of differences that would be considered unimportant is not defined in the record. The most defensible reading is that the estimate is uncertain and the registry results do not precisely determine the size or direction of 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 planning figures are participants per arm, not total event counts. They are illustrations based on the observed effect, using a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The planned effect to detect is varied as a stated fraction of the observed effect. The trial's own original design assumptions are not reported in the registry record.

For planning around 100% of the observed effect, the figures are 275 participants per arm for 80% power and 368 participants per arm for 90% power. For planning around 75% of the observed effect, they are 488 participants per arm for 80% power and 654 participants per arm for 90% power. For planning around 50% of the observed effect, they are 1,098 participants per arm for 80% power and 1,470 participants per arm for 90% power.

In plain terms, 80% power means that a study designed under the stated assumptions would have an 80% chance of detecting the chosen effect at the stated significance level if that effect were truly present and the assumptions held. The 90% column uses the same interpretation with a higher planned chance of detection. Higher planned power requires more participants under these assumptions. The figures are planning illustrations, not observed power.

The smaller-effect rows require more participants because a smaller difference is harder to distinguish from natural variation. These calculations use the observed effect as their starting point, so they should not be mistaken for evidence that the observed effect is stable or that it is the effect a future study should target. They also do not show that the original trial was designed with these assumptions.

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 = -0.300; pooled standard deviation σ = 1.254.
2. n = 2 × (1.96 + 0.842)² × 1.254² / -0.300² = 274.5, rounded up to 275 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 <- -0.3                      # observed difference in means
sigma <- 1.25444663642435                     # 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(666029)
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 = 275 (80% power), 368 (90% power)
 75% of observed effect: n per arm = 488 (80% power), 654 (90% power)
 50% of observed effect: n per arm = 1,098 (80% power), 1,470 (90% power)
power.t.test: 275.4 
Simulated power at n = 275 per arm: 0.803 (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 registry lists two outcome measures, but the posted results described for this analysis identify a primary endpoint and no posted secondary analyses. The number of analyses is listed as zero. The record does not explain whether secondary outcomes were measured, whether results were withheld, or how the outcome-measure count relates to the posted analysis count. A complete assessment of selective reporting is therefore not possible from the registry record.

Multiplicity arises when several outcomes, comparisons, or analysis choices are examined. In general, the more tests considered, the greater the chance that at least one result appears notable by chance if each is interpreted without regard to the others. The registry record does not report a multiplicity adjustment, a hierarchy for secondary outcomes, or a prespecified plan for controlling multiple testing. It is not appropriate to assume that an adjustment was or was not used beyond what the record states.

The primary-outcome description says data were missing for two participants in the atorvastatin arm and two participants in the placebo arm. The arm summaries report 17 and 18 participants, respectively. The record does not explain why data were missing, whether the missingness occurred before or after randomization, or how missing values were handled. It also does not report sensitivity analyses for missing data. These omissions matter because missingness can affect the estimate if the observed measurements do not represent the intended analysis population.

The registry does not identify an intention-to-treat, per-protocol, or other analysis population. It does not state whether all randomized participants were included in the primary comparison or whether the analysis was restricted to participants with observed endpoint values. The posted counts should therefore be read as the counts reported with the outcome, not as proof of a particular analysis population.

The record also does not report interim analyses, stopping rules, or a detailed statistical analysis plan. Those details are relevant to understanding the context in which an analysis was selected and interpreted. Without them, the posted primary comparison can be described, but the prespecification and full analytical handling cannot be independently assessed from the registry record.

14. 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 0% reporting threshold.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: muscle ache (5.0%).

The adverse-event record lists 20 participants at risk for serious adverse events in each arm. It reports one serious adverse event considered related in the atorvastatin arm and none in the placebo arm. For other adverse events, the record reports zero considered related in either arm. These are the registry's reported figures; they do not establish that all events were captured or that the risk is precisely characterized.

The deaths fields are not populated with counts, so death counts are not reported in the registry record. The record lists muscle ache at 5.0% among the top serious-event terms, but does not provide a corresponding count in the information recorded. The term should not be interpreted as a complete description of event severity, timing, duration, or causality beyond what the registry explicitly reports.

Safety counts from a trial of this size and duration can be imprecise, especially when events are uncommon. The record does not provide detailed event narratives, all-cause adverse-event totals, exposure-adjusted rates, or a fuller assessment of follow-up. The listed numbers are descriptive safety information, not a basis for medical advice or a definitive comparison of safety between treatments.

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

The registry result describes a mean difference in skeletal muscle microvascular function at 6 months between the atorvastatin and placebo arms. The observed means were 3.7 and 4.0, and the posted mean difference was -0.3. The confidence interval, from -1.137 to 0.537, is consistent with more than one possible direction and size of difference. The unadjusted p-value was 0.483. Together, these values indicate that the posted comparison does not precisely determine the difference between the arms.

This finding does not establish that the treatments are equivalent. Equivalence requires a defined margin and an analysis designed to assess whether effects fall within that margin; no such margin is reported in the registry record. Nor does the result show that there is no effect. An uncertain estimate can reflect limited precision, and the interval includes a range of possible contrasts.

The endpoint is a physiological measure of muscle microvascular function, described through Kf. It is not a direct measure of clinical events, symptoms, or day-to-day function. The registry record does not report how changes in this endpoint correspond to outcomes that participants would experience, or what size of change would be clinically important. The trial's stated research question concerns muscle microvascular blood flow, but the posted endpoint alone cannot resolve broader questions about health outcomes.

The result also does not demonstrate that atorvastatin caused the observed difference. Randomization and masking are reported, but important design and analysis details are not reported, including the randomization method, the analysis population, and the handling of missing data. The record notes missing primary-outcome data in both arms. These gaps limit how strongly the reported estimate can be interpreted as a causal treatment effect.

In short, the registry reports an uncertain comparison on a specific physiological endpoint in a completed phase 2 study. It neither establishes a clinically meaningful benefit nor rules one out. It should not be generalized beyond the population, endpoint, follow-up, and analytical information recorded in the registry.

16. Why This Trial Matters Statistically

This trial is statistically interesting because its primary outcome is a continuous physiological measure rather than a clinical event. A mean difference preserves the scale of that measure, while the standard deviations and confidence interval show how much uncertainty accompanies the comparison. The result illustrates why an estimated difference, its interval, and the context of measurement all matter together.

The estimate is -0.3, but the confidence interval spans -1.137 to 0.537. Looking only at the point estimate would conceal the range of values compatible with the data. Looking only at the p-value of 0.483 would also lose information about direction and magnitude. Reading these summaries together makes clear that the result is not precise enough to isolate a narrow treatment contrast.

The measurement description adds another statistical layer. Kf is derived from a relationship between filtration and cuff pressure, and the record reports a coefficient of variation of 14.5%. This highlights that conclusions about treatment differences depend not only on the number of observations but also on the reliability and variability of the measurement process. The record does not provide further repeatability analyses, so the impact of measurement variation cannot be separated from other sources of uncertainty.

The record also illustrates the importance of transparent reporting. Randomized allocation and double masking are listed, but the model is coded as single group, despite separate arms and an intervention comparison. Missing endpoint data are noted, while the method for handling them is not. The analysis population and original statistical plan are not reported. These details influence how a reader should assess precision, possible bias, and reproducibility.

Finally, the sample-size illustrations make visible how planned precision depends on the effect a study aims to detect. Smaller target effects require more participants under the stated assumptions. Because the illustrations are anchored to the observed effect and the original design assumptions are unavailable, they are best understood as planning context rather than as evidence about the trial's original design or its observed power.

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 registry record offers limited detail about the trial's conduct and analysis. Although randomization and double masking are listed, the sequence-generation method, allocation concealment, masking roles, and baseline characteristics are not reported. The single-group model coding does not align clearly with the randomized allocation and separate arm summaries, and the record does not explain this discrepancy.

The endpoint description notes missing data on two participants in each arm, but the reasons, timing, and handling of those missing values are not reported. The analysis population is also not stated. Without that information, readers cannot determine whether the comparison represents all randomized participants or only those with observed measurements. No sensitivity analysis is posted to show how alternative assumptions about missing data might affect the result.

The outcome is a technical physiological measure. While the registry describes how Kf was assessed and reports a coefficient of variation of 14.5%, it does not report a clinically meaningful threshold for the endpoint or explain how the measure relates to symptoms or longer-term clinical outcomes. The posted result therefore has a narrow interpretation tied to this measurement at 6 months.

The record reports two outcome measures but no posted secondary analyses and lists zero analyses. It does not provide the original statistical analysis plan, details of any interim analyses, or a multiplicity strategy. The method used for the confidence interval and p-value is not reported. These omissions limit assessment of prespecification and analytical choices.

Safety reporting is also brief. The record lists serious-event relatedness figures and a serious-event term, but does not supply detailed event descriptions, death counts, or a comprehensive account of follow-up. The listed data should not be treated as a complete safety profile. These limitations do not erase the posted result, but they restrict the strength and scope of conclusions that can be drawn from the registry record.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Implications for Treatment of the Metabolic Syndrome — NCT00666029.
• Registry record last updated 2019-01-23; status last verified 2019-01.
• Results first posted 2016-06-09.
• 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 record describes a completed phase 2 study titled “Implications for Treatment of the Metabolic Syndrome,” sponsored by University Hospital Southampton NHS Foundation Trust. It reports randomized allocation, double masking, a single-group model code, enrollment of 40, and a start date of 2006-02 with primary completion in 2008-02. The brief summary describes characterization of metabolic syndrome features and a randomized comparison of atorvastatin with placebo.

The primary endpoint was mean skeletal muscle microvascular function at 6 months. The posted means were 3.7 for atorvastatin and 4.0 for placebo; the mean difference was -0.3, with a confidence interval from -1.137 to 0.537 and an unadjusted p-value of 0.483. The registry notes missing endpoint data in both arms. Its analysis population, missing-data method, original design assumptions, and detailed statistical plan are not reported in the registry record.