Vertebrobasilar Flow Evaluation and Risk of Transient Ischemic Attack and Stroke (VERiTAS): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Vertebrobasilar Flow Evaluation and Risk of Transient Ischemic Attack and Stroke (VERiTAS) (NCT00590980), a registered phase not stated study. The primary outcome is Fatal and Nonfatal Ischemic Stroke in the Vertebrobasilar Territory.

2. Clinical Question

3. Trial Design

VERiTAS is registered as a completed study sponsored by University of Illinois Chicago. The record gives a study start of 2008-07, primary completion of 2014-07, and enrollment of 82. These are registry entries; they do not establish how many participants contributed data to the primary endpoint or to the adverse-event summaries.

The record describes an Observation group consisting of patients with intracranial or extracranial vertebrobasilar occlusion or stenosis ≥ 50% who presented with a vertebrobasilar-distribution transient ischemic attack or stroke. It does not describe a randomized allocation or a treatment-control comparison. Allocation is not stated, and the record explicitly cautions that the arms are not a like-for-like control comparison. The low-flow versus normal-flow contrast belongs to the research question, but separate flow-group details are not reported in the registry record.

The primary outcome is fatal and nonfatal ischemic stroke in the vertebrobasilar territory, assessed over up to 27 months. The endpoint is expressed as participants with an event, rather than a reported event rate or a treatment effect. The registry record lists one outcome measure and zero analyses. It does not report the primary endpoint’s group-specific results, an effect estimate, or an uncertainty interval. Further details about study procedures, follow-up completeness, and the 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

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Study participants meeting all inclusion and exclusion criteria

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: Analysis population consists of all participants meeting all inclusion/exclusion criteria

6. Primary Endpoint

The registry lists the primary outcome as Fatal and Nonfatal Ischemic Stroke in the Vertebrobasilar Territory, measured over up to 27 months.

The primary endpoint counts participants with a definite fatal or nonfatal ischemic stroke in the vertebrobasilar territory. Its stated timeframe is up to 27 months, and the endpoint population is study participants who meet all inclusion and exclusion criteria. The registry describes the measure as a count of participants. It does not include transient ischemic attack in the named primary endpoint, even though the study’s broader objective refers to stroke or transient ischemic attack.

A territorial stroke endpoint focuses the outcome on ischemic strokes occurring in the vascular territory relevant to vertebrobasilar disease. In general, a participant-count endpoint indicates whether an eligible participant experienced the defined event during the specified follow-up; it is different from a count of every event if a participant can have repeated events. The registry does not report whether recurrent events were analyzed separately or how event timing was handled.

In general, a clearly defined clinical endpoint helps connect a research question to an observable outcome. Here, the endpoint is relevant to the stated concern about subsequent stroke, but the record does not provide the results needed to quantify the relationship between blood-flow category and stroke occurrence. No primary endpoint estimate or analysis is reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes the primary endpoint as a count of participants with a binary event: definite fatal or nonfatal ischemic stroke in the vertebrobasilar territory. The outcome is therefore framed around whether the defined event occurred for a participant during follow-up. In general, binary outcomes can be summarized as event counts and denominators, and compared using a difference, ratio, or model-based measure. Which summary is appropriate depends on the design and analysis plan. The registry record does not report a primary endpoint estimate or an analysis method.

What does a participant-count endpoint tell us?

A participant count is not automatically an event rate. A rate usually relates events to a quantity of follow-up time, while a participant-count summary identifies participants meeting an event definition. The registry gives a timeframe of up to 27 months but does not report person-time, time-to-event estimates, or how varying follow-up duration was handled. It also does not report whether recurrent strokes were considered beyond the participant-level endpoint. No further assumptions about those choices can be made from the registry record.

In general, the denominator is essential for interpreting a count. The registry identifies the eligible endpoint population but does not report primary outcome denominators or counts. Enrollment of 82 should not be treated as the number analyzed: enrollment and endpoint analysis populations need not be identical, and the record does not specify the number included in any primary endpoint analysis. It does not report missing endpoint assessments or follow-up completion.

How should uncertainty be understood?

In general, an effect estimate summarizes a comparison, and its confidence interval communicates statistical uncertainty around that estimate under the analysis assumptions. A wide interval indicates less precision; a narrow interval indicates greater precision. Neither an interval nor a p-value establishes causality in a nonrandomized comparison. Here, no primary endpoint estimate, confidence interval, or p-value is reported, so the precision of any association cannot be evaluated.

In general, statistical significance is not the same as clinical importance. A p-value is interpreted relative to a statistical model and a null hypothesis; it does not directly give the probability that a hypothesis is true. The registry record does not report a primary endpoint test, its null hypothesis, or its significance level. The planning assumptions mention a two-sided significance level of 0.05 for sample-size illustrations, but that planning assumption is not a reported result or evidence of the analysis used for the trial.

What do the sample-size assumptions represent?

The stated sample-size approach is a planning illustration based on the observed effect, not the trial’s own design. It assumes equal allocation between two arms, a normal approximation, a two-sided significance level of 0.05, and an effect to detect expressed as a stated fraction of the observed effect. For time-to-event calculations, the stated output is the total number of events using the Schoenfeld approach; for other calculations, it is participants per arm. These are planning conventions, not observed outcomes or observed power. The numerical planning outputs and the observed effect used for them are not reported in the registry record.

In general, a planning calculation asks what sample size might be needed under specified assumptions. It does not show that a completed study had that sample size, that the assumptions were met, or that an observed result is reliable. A sample-size illustration based on an observed effect also depends on that effect estimate; without the primary analysis, readers cannot assess its basis from the registry record.

Does over-dispersion apply?

Over-dispersion matters in count models when observed variability is greater than the model expects; if ignored, uncertainty can be understated. That general issue is distinct from a participant-level binary endpoint, which is not itself a repeated event count. The record identifies a count of participants with an event and reports no dispersion parameter or count-model analysis. Whether any separate model was used is not reported in the registry record.

Overall, the available methods information supports a description of the outcome definition and the assumptions stated for planning illustrations. It does not support reconstruction of the primary outcome analysis, its adjustment strategy, its uncertainty, or its handling of incomplete follow-up.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Study Participants")
n      <- c(72)
events <- c(72)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Study Participants  72  72  100.0  95.0  100.0  94.9  100.0  95.1  100.0

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists one outcome measure and zero analyses. It identifies the primary endpoint but does not report a statistical analysis of that endpoint. It also does not report a multiplicity strategy, such as how inference would be handled across multiple outcomes, subgroups, or repeated analyses. With no endpoint analyses reported, the impact of any multiplicity approach cannot be assessed.

Missing data can affect an analysis if participants do not have an observed endpoint assessment or if follow-up ends before the outcome can be determined. In general, interpretation depends on how much information is missing, why it is missing, and how the analysis handles it. The registry record does not report missing-data counts, reasons for missingness, imputation methods, or sensitivity analyses. Follow-up is described as up to 27 months, but completeness and individual follow-up duration are not reported.

The primary endpoint population is described as participants meeting all inclusion and exclusion criteria. This identifies the intended eligible population, but the record does not specify the actual primary-analysis population or how eligibility deviations were handled. It does not report whether all eligible participants were included in an analysis, or whether any exclusions occurred after enrollment. Enrollment of 82 does not establish the denominator for the primary endpoint.

These omissions prevent assessment of whether missingness or analysis-population choices could have influenced an estimated relationship between blood flow and stroke. No assumptions about those choices should be inferred from the listed endpoint definition alone.

12. 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.

The adverse-event summary lists the Observation group with 72 at risk. It records 0 serious adverse events and 0 other adverse events, and lists 1 death. These are the registry’s adverse-event figures; they are not a comparison of low-flow and normal-flow groups, and they are not the reported result for the primary stroke endpoint.

The record does not provide a cause of death or say whether the death met the primary endpoint definition. It also does not list serious-event terms. Therefore, the death cannot be classified from this summary as a vertebrobasilar ischemic stroke, and the zero adverse-event counts should not be read as evidence that no participant experienced the primary outcome.

In general, adverse-event counts describe recorded events under the categories and reporting procedures used. Without comparison groups that are appropriately comparable and without details about ascertainment, follow-up, and event attribution, they do not establish whether an exposure caused or prevented an event. The registry explicitly cautions that this is not a randomized, like-for-like comparison. The safety figures should be read descriptively and separately from the unreported primary endpoint analysis.

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

The registry record establishes the study’s question and endpoint definition, but it does not establish the result of the main comparison. It describes patients with symptomatic vertebrobasilar disease and asks whether low blood flow on MR imaging is associated with greater subsequent risk than normal blood flow. The primary endpoint is definite fatal and nonfatal ischemic stroke in the vertebrobasilar territory over up to 27 months. No analysis of that endpoint is reported.

Accordingly, the posted registry information does not show whether low flow was associated with more or fewer strokes, how large any association might have been, or how precise an estimate would be. It also does not establish whether flow category predicts transient ischemic attack, since the named primary endpoint concerns stroke and no comparative results are reported for the broader objective. Absence of an analysis in the registry record is not evidence that the outcome did not occur.

The study is not described as a randomized comparison. Even if a flow-category association were reported elsewhere, an observational contrast would need to be interpreted with attention to differences between the groups and the analysis used to address them. The registry record does not report the flow-group results, adjustment methods, or analysis details needed to evaluate such a contrast.

The adverse-event counts have a narrower meaning: they are recorded figures for the Observation group, with 72 at risk, 0 serious adverse events, 0 other adverse events, and 1 death. They do not identify the cause of death or supply the missing stroke comparison. The enrollment count of 82 likewise does not indicate the primary endpoint denominator.

Thus, the defensible conclusion is about what the record documents: a completed study, a defined clinical question, a specified primary stroke endpoint, and limited adverse-event figures. The magnitude, direction, and precision of the relationship between blood flow and subsequent stroke are not reported in the registry record.

14. Why This Trial Matters Statistically

VERiTAS addresses a question about whether variation in blood flow is associated with subsequent cerebrovascular events among patients with symptomatic vertebrobasilar disease. Statistically, that question requires more than an outcome definition: it requires clear flow-group classification, outcome ascertainment, denominators, and an analysis that estimates the association and its uncertainty. The registry record supplies the question and names the primary endpoint, but does not report the primary analysis.

The record also illustrates why study design matters when reading comparisons. It explicitly says the study is not a randomized comparison and that the arms are not a like-for-like control comparison. A contrast between naturally occurring flow categories would be interpreted as an association unless the design and analysis support stronger conclusions. Information about adjustment and the composition of the flow groups is not reported in the registry record.

The endpoint definition is another important statistical feature. It specifies fatal and nonfatal ischemic stroke in the vertebrobasilar territory, whereas the broader objective also mentions transient ischemic attack. Keeping those outcomes distinct prevents readers from assuming that a result for one automatically answers questions about the other. Here, no primary outcome analysis is reported, so neither can be quantified from the registry information.

Finally, the record distinguishes study enrollment, an endpoint’s intended population, and the group listed in the adverse-event summary. Those quantities serve different purposes and should not be substituted for one another. The planning assumptions likewise describe hypothetical sample-size calculations rather than results or the trial’s own design. These distinctions are central to sound interpretation of clinical research.

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 main limitation for interpreting the primary question is that the registry record reports no primary endpoint analysis. It provides no outcome counts by flow category, denominators for the primary endpoint, effect estimate, confidence interval, or p-value. As a result, the direction, magnitude, and precision of any association cannot be assessed.

The record does not provide separate descriptions or sizes for the low-flow and normal-flow groups. It states that allocation is not stated and that the arms are not a like-for-like control comparison. Details about confounders, adjustment, or other methods for addressing differences between groups are not reported in the registry record. This prevents assessment of how a comparison would account for group differences.

Although the study objective mentions stroke or transient ischemic attack, the named primary endpoint is ischemic stroke in the vertebrobasilar territory. The registry does not report an analysis of transient ischemic attack or explain how it relates to the primary endpoint. It also does not report whether repeat events, event timing, or incomplete follow-up were handled in a particular way.

Enrollment is listed as 82, but the primary-analysis denominator is not reported. The adverse-event summary uses 72 at risk in the Observation group and lists 1 death without a cause. Those data cannot fill the primary endpoint gap. The record also does not report detailed eligibility criteria, missing-data methods, or the analysis population actually used. These limitations are specific to what is documented and should not be resolved by assumptions.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Vertebrobasilar Flow Evaluation and Risk of Transient Ischemic Attack and Stroke (VERiTAS) — NCT00590980.
• Registry record last updated 2026-04-15; status last verified 2026-04.
• Results first posted 2017-11-17.
• 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

VERiTAS is a completed study sponsored by University of Illinois Chicago, with enrollment of 82. The record gives a study start of 2008-07 and primary completion of 2014-07. It describes an Observation group of patients with symptomatic vertebrobasilar occlusion or stenosis ≥ 50%.

The research objective asks whether low blood flow on MR imaging is associated with subsequent stroke or transient ischemic attack compared with normal blood flow. The primary endpoint is definite fatal and nonfatal ischemic stroke in the vertebrobasilar territory among eligible participants, over up to 27 months. The registry lists one outcome measure and zero analyses; no primary endpoint results are reported.

The adverse-event summary lists 72 at risk, 0 serious adverse events, 0 other adverse events, and 1 death for the Observation group. The cause of death and its relationship to the primary endpoint are not reported. The study is not a randomized comparison, and the registry cautions that the arms are not like-for-like controls.