Cardiac CT's Role in Asymptomatic Patients With Diabetes and Metabolic Syndrome: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Cardiac CT's Role in Asymptomatic Patients With Diabetes and Metabolic Syndrome (NCT01564485), a randomized na study. The primary outcome is Systolic BP Pressure.

2. Clinical Question

3. Trial Design

The registry identifies this as a randomized study and lists two groups: cardiac CT and usual care. It also records masking as none and classifies the study model as single group. Those registry classifications do not align neatly with the two listed groups, so the design description should be read with that qualification. The record does not explain the single-group classification or provide further detail about the randomization process, such as sequence generation or allocation concealment.

The listed intervention was cardiac CT, a diagnostic test intended to provide a non-invasive assessment of the coronary arteries. Usual care was described as continued medical care with a primary care physician. The registry identifies the University of California, Irvine as sponsor. The study status is completed, with a start date of 2008-07 and primary completion date of 2016-12. Phase is listed as NA.

Enrollment is recorded as 193. For the primary systolic blood pressure outcome, the registry reports 75 participants in the cardiac CT group and 72 in the usual-care group. These outcome counts are not a substitute for the overall enrollment figure, and the registry does not explain the difference between them. It also does not report the original sample-size justification, recruitment targets by group, or the reasons any enrolled participants may not appear in the outcome results.

The outcome description specifies five-year follow-up, with assessments every six months. The record does not provide further details about the timing of the posted group means, adherence to the planned assessment schedule, or how the analysis handled measurements collected at different visits. No posted statistical analyses are listed.

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

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 Systolic BP Pressure, measured over Five year follow up.

The primary endpoint is systolic blood pressure, measured in mm Hg and treated as a continuous outcome. The registry describes the assessment at five-year follow-up and says blood pressure was to be assessed every six months during the follow-up period. The intended comparison concerns whether control of systolic blood pressure differed between participants assigned to cardiac CT and those assigned to usual care.

A continuous measure retains the numerical values of the measurements rather than dividing participants into categories. A group mean gives a measure of the average observed value, while the standard deviation describes how dispersed individual measurements are around that average. The registry reports a mean of 145 mm Hg and a standard deviation of 6 mm Hg for cardiac CT, and a mean of 144 mm Hg and a standard deviation of 5 mm Hg for usual care.

Blood pressure is a risk factor measure, which makes it relevant to the study’s stated focus on risk factor control. In general, comparing the group means can describe how the average recorded measurement differed between the randomized groups. The measure alone does not explain why any difference occurred, establish the pathway through which care may have affected blood pressure, or describe outcomes beyond this endpoint. The registry does not report a separate endpoint definition, measurement protocol, or analysis population description.

7. Results Posted in the Registry

• Cardiac CT: mean 145.00 versus 144.00 on control; difference 1.00 (95% CI -0.78 to 2.78), standardized effect d = 0.18; z-test p = 0.272.

8. Statistical Interpretation

9. Statistical Methods Explained

The main outcome is continuous, so the registry reports a mean and standard deviation for each group. A mean is the arithmetic average of the recorded measurements. A standard deviation describes the spread of measurements around that average; it is not the uncertainty around the mean and is not a confidence interval. Here, the cardiac CT group is reported with a mean of 145 mm Hg and standard deviation of 6 mm Hg, while usual care is reported with a mean of 144 mm Hg and standard deviation of 5 mm Hg.

What does the mean difference represent?

The mean difference is the estimated contrast between the two group averages. The registry reports a mean difference of 1.0 mm Hg, with the cardiac CT group’s mean higher than the usual-care mean. This is an absolute difference in the units of the outcome, rather than a percentage difference. It describes the estimated contrast in the posted results; interpretation as a causal effect depends on design and analysis details that are not fully documented in the registry record.

What does the confidence interval add?

A confidence interval gives a range of values that are compatible with the observed data under the statistical model used to calculate it. It conveys uncertainty about the estimated mean difference. The interval for this comparison extends from a value below zero to 2.783, and therefore includes zero. Inclusion of zero means the data do not clearly distinguish the estimated contrast from no mean difference. It does not prove the true difference is zero, and it does not mean that every value in the interval is equally plausible.

The width of a confidence interval depends on the amount of information in the data and the variability of the outcome, as well as the method used to calculate the interval. More observations or less variability can generally yield a more precise estimate, all else being equal. The registry does not report the specific interval-construction method or the analysis details behind the posted estimate.

How should the p-value be read?

The unadjusted p-value is 0.272. In general, a p-value describes how inconsistent the observed data, or data more extreme, would be with a specified null model if that model were true. It is not the probability that the null hypothesis is true, and it does not measure the size or importance of a difference. A p-value also does not reveal whether assumptions were met, whether data were missing, or whether the analysis was selected before looking at results.

The registry does not list posted statistical analyses, so the details of the inferential procedure are not reported in the registry record. The posted p-value should be read alongside the estimate and confidence interval, rather than as a stand-alone conclusion. The direction and size of the estimated difference, its uncertainty, and the data included in the analysis all matter to interpretation.

Why does the study structure matter?

Random assignment can, in general, support a fair comparison by creating groups that are comparable on average at the point of assignment. It does not eliminate the importance of follow-up, missing data, adherence, or analysis choices. The record identifies the study as randomized but also labels its model as single group while listing two groups. It does not explain that classification, the randomization procedures, or the analysis population. These gaps make it important not to infer more than the posted comparison establishes.

The endpoint description also refers to assessments every six months, whereas the primary outcome is identified at five-year follow-up. Repeated measurements can be analyzed in different ways, for example by selecting a specified visit or by modeling measurements over time. The registry does not report which approach was used for the posted means, whether all scheduled assessments contributed, or how within-person correlation was handled. No particular repeated-measures method can therefore be attributed to this comparison.

Finally, the listed outcome counts are 75 and 72, while total enrollment is 193. The reason those numbers differ, and whether the posted means use all available measurements or a defined subset, are not reported in the registry record. This affects how confidently the estimates can be generalized to all randomized participants.

10. Confidence Intervals and Precision

The estimated mean difference is 1.0 mm Hg, and its confidence interval extends from below zero to 2.783 mm Hg. Because the interval crosses zero, it includes both a small negative difference and a positive difference of the size at its upper endpoint. The interval therefore reflects uncertainty about both the direction and the size of the underlying mean contrast.

Precision is about how narrowly the data locate an estimate, not whether a result is important or whether a treatment is effective. A confidence interval gives more information than a point estimate alone: it shows a set of values compatible with the data and the interval’s statistical assumptions. In general, a wider interval indicates less precision, while a narrower one indicates greater precision. No threshold for a meaningful blood pressure difference is reported in the registry record, so the clinical importance of the range cannot be determined from this record alone.

The group standard deviations are 6 mm Hg for cardiac CT and 5 mm Hg for usual care. These describe variation among measurements in the analyzed groups, rather than uncertainty in the estimated group means. The outcome counts are 75 and 72. The registry does not explain the relationship between these counts and overall enrollment, or report how missing measurements were treated. That information would help assess whether the interval’s precision reflects all randomized participants or a subset.

The confidence interval should not be interpreted as guaranteeing that the true difference lies within its limits. It is a statistical summary whose meaning depends on the model and analysis procedure. Details of the interval method are not reported in the registry record. Taken together, the estimate, interval, and p-value describe an uncertain comparison rather than a precise separation of the group averages.

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 events. The outcome is continuous, so the figures describe the number of participants needed in each of two arms under the stated planning assumptions. They are illustrations based on the observed effect, not the trial’s original design calculation. The registry’s own design assumptions and sample-size justification are not reported in the registry record.

The planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effects considered are 100%, 75%, and 50% of the observed effect. For 100% of the observed effect, the illustration gives 481 participants per arm for 80% power and 644 per arm for 90% power. For 75% of the observed effect, it gives 855 and 1,144 participants per arm, respectively. For 50% of the observed effect, it gives 1,923 and 2,574 participants per arm, respectively.

In plain terms, 80% power means that if the specified effect and planning assumptions were true, this design would have an 80% chance of producing a statistically significant result using the stated threshold. The 90% column describes a higher target chance under those same assumptions. These figures are not observed power: they are hypothetical planning illustrations, not a measure of how likely the completed study was to detect an effect after observing its results.

The figures increase as the assumed effect gets smaller. Smaller differences are harder to distinguish from random variation, so more participants are generally needed to detect them at a given power and significance level. These calculations use the observed effect as their reference, and the observed effect itself is uncertain. The planning numbers should therefore be read as conditional illustrations, not as a recommended design or proof that the original study was adequately or inadequately sized.

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 = 1.000; pooled standard deviation σ = 5.533.
2. n = 2 × (1.96 + 0.842)² × 5.533² / 1.000² = 480.6, rounded up to 481 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 <- 1                      # observed difference in means
sigma <- 5.53297326068437                     # 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(1564485)
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 = 481 (80% power), 644 (90% power)
 75% of observed effect: n per arm = 855 (80% power), 1,144 (90% power)
 50% of observed effect: n per arm = 1,923 (80% power), 2,574 (90% power)
power.t.test: 481.5 
Simulated power at n = 481 per arm: 0.801 (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 three outcome measures overall, but reports no posted secondary outcomes. It lists zero posted statistical analyses. Consequently, the record does not show how many comparisons were planned, whether any secondary measures were tested, or what strategy was used to address multiplicity. Multiplicity arises when several hypotheses or outcomes are assessed; without information about the planned comparisons and analysis, it is not possible to judge whether adjustment was appropriate or necessary.

The primary comparison is reported with an unadjusted p-value of 0.272. No adjusted p-value or multiplicity procedure is listed. The registry does not report whether the primary outcome and time point were prespecified in a protocol or statistical analysis plan, nor does it describe any interim analyses. The timing and rationale of analyses beyond the posted summary are therefore not reported in the registry record.

Missing data are also insufficiently described. Enrollment is recorded as 193, while the primary outcome results list 75 participants in the cardiac CT group and 72 in usual care. The registry does not state why the outcome counts differ from enrollment, whether these are the numbers randomized, assessed, or included in the analysis, or how unavailable measurements were handled. It does not report imputation, complete-case analysis, or sensitivity analyses for missing outcomes.

The analysis population is not specified. The registry does not say whether the comparison included all randomized participants according to assigned group, only participants who completed follow-up, or another subset. Such information matters because exclusions after randomization can affect how well the comparison preserves the balance created by random assignment. The record also does not describe adjustment for baseline blood pressure or other covariates. These omissions do not establish that a particular method was or was not used; they mean the methods are not reported in 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.

The registry lists zero serious adverse events in the cardiac CT group among 92 participants at risk, and zero in usual care among 93 participants at risk. It also lists zero other adverse events in the cardiac CT group among 92 participants at risk and zero in usual care among 93 participants at risk. These are the counts recorded in the adverse-event results.

The number at risk for adverse-event reporting differs from the number listed for the primary systolic blood pressure outcome. The registry does not explain the difference, define the adverse-event collection period, or provide further detail about event ascertainment. The zero counts should therefore be interpreted as the posted counts for the stated at-risk groups, not as evidence that no events occurred outside the recorded reporting framework.

Deaths are not reported in the registry record. No serious adverse-event terms are listed. The posted counts do not, on their own, establish comparative safety; they are descriptive registry entries without further information about follow-up, completeness, or event definitions.

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

The registry’s primary outcome results describe average systolic blood pressure at the stated five-year follow-up. The cardiac CT group has a reported mean of 145 mm Hg and the usual-care group a mean of 144 mm Hg. The estimated mean difference is 1.0 mm Hg, with a confidence interval that includes values on either side of zero. The unadjusted p-value is 0.272. Together, these statistics indicate that the posted data do not clearly distinguish the group means from no difference, while leaving uncertainty about the direction and size of any underlying difference.

That interpretation is not equivalent to saying the groups are identical. A result that does not clearly distinguish a difference from zero can reflect a small effect, substantial uncertainty, or both. The confidence interval provides the relevant range of statistical uncertainty, but the registry does not report a threshold for what would count as a clinically meaningful difference. Clinical importance cannot be settled by the p-value alone.

The result also concerns only the posted systolic blood pressure endpoint. It does not establish what happened to other risk factors, cardiovascular events, or longer-term outcomes. Although the study summary describes an interest in risk factor control, the registry does not post secondary outcome results. The absence of those results in the record is not evidence that no other outcomes were measured.

Finally, the registry does not provide enough detail to determine how the posted analysis handled missing measurements, repeated assessments, or the analysis population. The group counts for the primary outcome are lower than overall enrollment, and reasons are not reported. These limitations mean that the statistical comparison should be interpreted as a description of the posted outcome data, not as a complete account of the trial’s conduct or a definitive causal conclusion.

16. Why This Trial Matters Statistically

This trial is statistically interesting because it places a diagnostic procedure within a question about subsequent risk factor control. The primary outcome is a continuous measure, allowing the reported group means and mean difference to describe the scale and direction of the observed contrast. The confidence interval and p-value add information about uncertainty beyond the point estimate.

The result illustrates why statistical significance and effect size are not interchangeable. The estimated mean difference is 1.0 mm Hg, but the confidence interval includes zero and the unadjusted p-value is 0.272. A reader needs both the estimated contrast and its uncertainty to understand what the data indicate. Neither a single p-value nor the difference in means alone captures all relevant information.

The registry also highlights the importance of transparent reporting. It identifies randomization and two groups, but classifies the model as single group. It specifies repeated assessments and a five-year endpoint, yet does not explain the approach used to summarize or analyze those measurements. The outcome counts differ from overall enrollment, without an account of missing data or the analysis population. Those gaps constrain interpretation even when the headline statistics are available.

Finally, the planning illustrations show how sample-size requirements depend on the effect assumed for detection. Smaller target effects require more participants per arm under the listed assumptions. Because these are retrospective planning illustrations based on the observed effect rather than the trial’s own design justification, they cannot establish what the investigators planned or whether the study was prospectively sized for a particular effect. Separating that planning question from the observed result is essential to sound statistical interpretation.

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 leaves several trial-specific uncertainties. It calls the study randomized but lists the model as single group, even though it describes cardiac CT and usual-care groups. The record does not explain this classification or provide operational details about randomization, allocation concealment, or masking beyond stating that masking was none.

The outcome description specifies assessments every six months and identifies the primary outcome at five-year follow-up. It does not clarify which assessment contributed to the posted means or whether repeated measurements were analyzed together. The primary outcome results include 75 participants in the cardiac CT arm and 72 in usual care, compared with enrollment of 193. Reasons for the difference, the amount of missing data, and methods for handling missing measurements are not reported in the registry record.

The record does not provide baseline systolic blood pressure, so the posted group values cannot be interpreted as within-person change from baseline. It also does not describe the analysis population, covariate adjustment, protocol deviations, adherence to assigned care, or sensitivity analyses. The original sample-size justification and any interim analysis plan are not reported. No secondary results or posted statistical analyses are listed.

These reporting gaps do not show that the relevant procedures were absent; they mean the registry record does not document them. They limit assessment of how closely the posted estimate corresponds to the randomized comparison and how robust it may be to analysis choices. The results should accordingly be read as the registered summary of the primary endpoint, with the stated uncertainties.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Cardiac CT's Role in Asymptomatic Patients With Diabetes and Metabolic Syndrome — NCT01564485.
• Registry record last updated 2021-06-08; status last verified 2021-06.
• Results first posted 2021-06-08.
• 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 study of cardiac CT versus usual care in asymptomatic patients with diabetes, with diabetes and metabolic syndrome listed as conditions. It records enrollment of 193 and identifies systolic blood pressure at five-year follow-up as the primary outcome. The outcome was a continuous measure in mm Hg, with assessments described every six months.

The posted means are 145 mm Hg for cardiac CT and 144 mm Hg for usual care. The estimated mean difference is 1.0 mm Hg; the confidence interval includes zero, and the unadjusted p-value is 0.272. The primary outcome counts are 75 and 72, and the registry does not explain their difference from enrollment. No posted statistical analyses or secondary results are listed. Safety entries record zero serious and zero other adverse events in each group; deaths are not reported in the registry record.