RAAS and Arterial Stiffness in SCI: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for RAAS and Arterial Stiffness in SCI (NCT04510974), a registered phase not stated study. The primary outcome is Pulse Wave Velocity (m/s).

2. Clinical Question

3. Trial Design

The registry describes a completed study of people with spinal cord injury (SCI) and able-bodied controls. Its brief summary says the study examines differences in central arterial stiffness, orthostatic changes in blood pressure, norepinephrine and plasma renin between individuals with SCI and age-matched uninjured controls. The listed primary outcome is Pulse Wave Velocity (m/s), with a mean as the parameter and Standard Deviation as the dispersion measure. The outcome timeframe is “2 years.” The description says the average is to be determined among the three groups.

The groups are Cervical SCI, Thoracic SCI and Able-bodied Control. The cervical group description specifies ages 21-70, injury between C1-T1, wheelchair dependence, AIS classification of A, B or C, and injury more than 1 year ago. The thoracic group description specifies ages 21-70, injury between T6-T12, wheelchair dependence, AIS classification of A, B or C, and injury more than 1 year ago. Controls are described as ages 21-70. How participants were recruited, how age matching was done, and whether eligibility criteria were applied exactly as described are not reported in the registry record.

The registry lists enrollment of 33 and status COMPLETED. It gives a start date of 2018-06-30 and a primary completion date of 2020-12-01. The record does not state how many participants contributed data to each outcome. Allocation is not stated, and the record flags that this is not a randomized comparison and that the arms are not a like-for-like control comparison. It does not describe a treatment assignment, a randomization procedure, or a concurrent intervention group. Those omissions mean the group comparisons should not be read as randomized treatment effects.

Three secondary outcomes are named: Systolic Blood Pressure (mmHg), Plasma Renin (pg/ml) and Norepinephrine (pg/ml). The registry records four outcome measures overall. It does not report outcome values or analyses for the primary or secondary measures.

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 Pulse Wave Velocity (m/s), measured over 2 years.

Pulse Wave Velocity (m/s) is the primary endpoint. It is a measure of how quickly a pressure wave travels through the arterial system. In general, pulse wave velocity is used as an indicator of arterial stiffness: faster wave travel is associated with stiffer arteries. This is a statistical and physiological interpretation of the measure, not a result reported for these participants.

The registry specifies a mean and Standard Deviation for the outcome and describes the aim as determining the average among the three groups. A mean gives the central value of the observed measurements; a Standard Deviation describes how dispersed individual measurements are around that mean. Reporting both would help readers understand group-level values as well as participant-to-participant variability. The registry does not report those group means or Standard Deviations, nor does it provide a between-group estimate or a confidence interval. It is therefore not possible to establish from the registry record whether the group averages differed or how precisely they were estimated.

Pulse wave velocity is relevant to the study's stated interest in central arterial stiffness. It is not interchangeable with the secondary measures of systolic blood pressure, plasma renin or norepinephrine. Those outcomes describe different aspects of blood pressure or physiology. The primary outcome timeframe is recorded as “2 years,” but the precise timing of measurement and whether all participants were assessed at the same time point are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: pulse wave velocity is measured in m/s, and the registry specifies a mean and Standard Deviation. In general, continuous outcomes can be described by a mean when an average is informative, with the Standard Deviation indicating how spread out participant measurements are around that average. The Standard Deviation describes variability among measurements; it is not the same as the uncertainty in the estimated mean. The registry record does not report the actual mean or Standard Deviation for any group.

What would a group comparison estimate?

The stated aim is to determine average pulse wave velocity among the cervical SCI, thoracic SCI and able-bodied control groups. A comparison could report each group's mean and estimate differences between groups. In general, an estimate is more informative when accompanied by a confidence interval, which describes the uncertainty around that estimate under the assumptions of the analysis. The registry reports no group estimates, between-group contrasts or confidence intervals. It also does not identify a specific statistical test or model. No particular analysis should therefore be inferred from the endpoint description alone.

In general, the choice of method for comparing continuous measurements depends on the study design, measurement distribution, group sizes and analysis objective. Methods may also account for relevant participant characteristics where an analysis plan calls for adjustment. The registry record does not state whether the pulse wave velocity analysis used an unadjusted comparison, a regression model, covariate adjustment, or another approach. It does not report assumptions assessed or methods used if those assumptions were not met. This missing detail limits the ability to assess how any eventual estimate was obtained.

How should a p-value be read?

In general, a p-value describes how unusual data at least as incompatible with a specified null hypothesis would be if that null hypothesis and the model assumptions were true. It does not give the probability that the null hypothesis is true, and it does not quantify the size or practical importance of an effect. A p-value is best read alongside the estimated effect and its confidence interval. No p-value for the primary outcome or named secondary outcomes is reported in the registry record, so there is no posted significance test to interpret.

What does the planning illustration represent?

The stated sample-size planning assumptions are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The target effect is expressed as a stated fraction of the observed effect. Such calculations are planning illustrations: in general, they ask how many participants per arm might be needed to detect a specified effect under chosen assumptions. They are not evidence that the trial was designed or analyzed that way, and they are not observed power. The record does not report the trial's own sample-size justification, nor does it report the specific effect fractions or calculated participant requirements associated with the illustrations.

The illustration's equal allocation between two arms does not by itself describe the registered comparison among three groups. The registry does not identify which pairwise contrast, if any, was used for the planning calculation, or how the calculation relates to the three-group primary question. The observed effect on which the illustration is based is not reported in the registry record. Without the numerical estimates and planning details, the illustration cannot establish whether the enrolled sample was adequate for a particular comparison.

Why can variability and dispersion matter?

In general, measurements with substantial variability can yield less precise estimates of group averages or differences than measurements with little variability, all else being equal. A Standard Deviation helps describe this spread. A confidence interval describes uncertainty in an estimate and depends on the data and analysis; it is not simply another name for the Standard Deviation. The registry names the dispersion measure but posts no values, so variability and precision cannot be assessed for this study.

Over-dispersion is a general issue for certain count outcomes when variability exceeds what a chosen statistical model expects. It matters because an inappropriate variance assumption can lead to misleading uncertainty estimates. Pulse wave velocity is a continuous endpoint, not a count outcome, and the registry gives no indication that over-dispersion was relevant to its primary analysis. No count-outcome analysis method is reported.

What can be inferred from the analysis record?

The registry records zero analyses. That indicates no statistical analysis results are represented in the record; it does not establish that researchers performed no analyses outside the registry. The statistical plan, interim analyses, missing-data methods, analysis populations and multiplicity procedures are not reported in the registry record. Any claim about the methods actually used would therefore go beyond the information available. The registry entries support describing the endpoint, groups and stated planning assumptions, but not reconstructing the analysis.

10. Confidence Intervals for Each Arm

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

R code and output

arm <- c("Cervical SCI", "Thoracic SCI", "Able-bodied Control")
n   <- c(11, 11, 11)
m   <- c(8.81, 7.36, 5.53)
sp  <- c(1.91, 1.58, 0.95)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Cervical SCI  11  8.810  1.910  7.527  10.093
CARM  Thoracic SCI  11  7.360  1.580  6.299  8.421
CARM  Able-bodied Control  11  5.530  0.950  4.892  6.168

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome, Pulse Wave Velocity (m/s), and names three secondary outcomes: Systolic Blood Pressure (mmHg), Plasma Renin (pg/ml) and Norepinephrine (pg/ml). It records four outcome measures overall. When several outcomes or comparisons are examined, there can be multiple opportunities to identify a result that appears noteworthy by chance. In general, a statistical plan may address this by identifying a primary analysis in advance or using an adjustment procedure. The registry record does not report a multiplicity strategy, a hierarchy among secondary outcomes, or which comparisons were planned.

The record also does not describe missing-data counts, reasons for missing measurements, imputation, or a complete-case approach. It does not state which participants were included in each outcome analysis or define an analysis population. Enrollment of 33 does not establish that all enrolled participants contributed to every endpoint. The safety figures list 11 participants at risk per group, but those denominators do not establish the analysis denominators for pulse wave velocity or the secondary outcomes.

The registry records zero analyses and does not post outcome estimates, so the effects of missing data or multiple testing cannot be evaluated. In general, missingness can affect an estimate if the participants with observed data differ systematically from those without measurements. The direction or magnitude of such an effect cannot be inferred without information on missingness and analysis methods. The statistical plan, interim analyses and handling of repeated or multiple comparisons are not reported in the registry record.

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 registry lists 11 participants at risk in each group: Cervical SCI, Thoracic SCI and Able-bodied Control. For each group, it records 0 serious events, 0 other events and 0 deaths. No serious adverse event terms are listed. These are the posted safety counts and denominators.

A count of 0 means that the registry reports no events in that category for the participants listed as at risk; it does not establish that the true risk is zero. In general, an observed event count is a description of what was recorded during a study, while the underlying chance of an event remains uncertain. A zero count can coexist with uncertainty, particularly when the number of participants observed is limited. The record does not provide event definitions, observation duration by participant, ascertainment procedures, or details about whether all participants were monitored in the same way.

The safety entries should not be treated as evidence about the primary endpoint. They concern adverse-event counts, whereas pulse wave velocity is the continuous primary outcome. The registry's safety figures also do not provide a randomized comparison of harms: allocation is not stated, and the record cautions that the arms are not a like-for-like control comparison. The counts can be reported as recorded, but they do not support broader conclusions about safety beyond those entries.

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

The registry record establishes that the study was completed, enrolled 33 participants, and set out to examine pulse wave velocity and related blood-pressure and biochemical measures across cervical SCI, thoracic SCI and able-bodied control groups. It also documents the primary endpoint's units, summary measure and timeframe, as well as three named secondary outcomes. Those details define the research question and the outcomes the registry intended to track.

The record does not report the group measurements or statistical comparisons. It therefore cannot show whether average pulse wave velocity was higher, lower or similar in any group, nor can it indicate the size or precision of a difference. It also cannot establish whether systolic blood pressure, plasma renin or norepinephrine differed. The study's title, objectives, completed status and planned outcome descriptions are not substitutes for posted results.

In general, a comparison between participant groups is descriptive of those groups unless the design and analysis support a stronger causal interpretation. Here, allocation is not stated, the record flags that the comparison is not randomized, and it cautions that the arms are not a like-for-like control comparison. Potential group differences beyond SCI status cannot be assessed from the information reported. The registry does not describe adjustment methods that might address measured differences.

The listed sample-size calculations are planning illustrations, not observed power and not findings. They use stated assumptions, but the record does not report the observed effect or the numerical planning outputs needed to assess them. Similarly, the safety counts of 0 events in each listed category describe the registry entries; they do not prove that risks are absent.

Accordingly, the record supports a careful account of the study's question, groups, outcomes and missing statistical details. It does not support a conclusion about the direction, magnitude, statistical significance, clinical importance or causal meaning of the study's outcome findings.

14. Why This Trial Matters Statistically

This study is statistically interesting because it asks about a continuous measure of arterial stiffness across groups defined by injury level and an able-bodied comparison group. The primary endpoint is expressed as a mean with Standard Deviation, making both the group averages and the spread of measurements relevant to interpretation. The study description also includes blood-pressure changes and biochemical measures, which represent related but distinct outcomes.

The registry record highlights an important design distinction: this is not described as a randomized comparison, allocation is not stated, and the record cautions that the arms are not a like-for-like control comparison. In general, group differences in such settings cannot automatically be attributed to the group-defining condition. Clear reporting of group characteristics, outcome data, analysis methods and uncertainty would be important for judging how robustly the comparisons address the stated question. Those outcome and analysis details are not reported in the registry record.

The record also illustrates why a completed status and a well-defined endpoint do not suffice to interpret findings. Without group means, variability, effect estimates and confidence intervals, readers cannot assess the size or precision of a difference. Without the analysis plan, missing-data approach and multiplicity handling, readers cannot evaluate how the reported comparisons were selected or analyzed. The registry records zero analyses, so those considerations remain unresolved.

Finally, the sample-size assumptions need to be distinguished from observed results. Planning illustrations based on an assumed effect and statistical model are not an assessment of the study's actual evidential strength. The record's details allow the planning assumptions to be described, but not the numerical outputs or their relation to the three-group question. The main statistical lesson is the difference between a stated research question, a design description and the evidence required to interpret an outcome.

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.

A central limitation of interpretation is that the registry record reports no primary or secondary outcome values and records zero analyses. Group means, Standard Deviations, contrasts, confidence intervals and p-values are not reported. As a result, the statistical findings cannot be reconstructed or assessed for size, direction or precision.

The design details are also limited. The record does not state allocation, and it cautions that the comparison is not randomized and that the arms are not a like-for-like control comparison. The registry does not report how controls were selected or matched, whether relevant participant characteristics were balanced, or whether any covariate adjustment was used. The brief summary calls controls age-matched, but the matching procedure is not described; the arm description gives the age range only.

Although the registry gives enrollment of 33 and descriptions of the three groups, it does not report outcome-specific denominators or participant flow. Missing measurements, exclusions from analyses, reasons for missingness and analysis populations are not described. The timeframe is listed as “2 years,” but the timing and consistency of endpoint assessment are not detailed.

The record does not provide the statistical analysis plan, sample-size justification for the trial, interim-analysis information, multiplicity procedures or methods for handling missing data. It identifies planning assumptions but not the numerical outputs or the observed effect used for those illustrations. Safety reporting is limited to counts and participants at risk, without event definitions or further monitoring details. These gaps constrain both statistical and clinical interpretation; they do not establish that unreported procedures or events did not occur.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: RAAS and Arterial Stiffness in SCI — NCT04510974.
• Registry record last updated 2025-02-20; status last verified 2025-02.
• Results first posted 2025-02-20.
• 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

NCT04510974, titled “RAAS and Arterial Stiffness in SCI,” is listed as COMPLETED, with enrollment of 33. The study concerns pulse wave velocity and related measures in cervical SCI, thoracic SCI and able-bodied control groups. The primary outcome is mean Pulse Wave Velocity (m/s), with Standard Deviation as the dispersion measure and a timeframe of “2 years.” Named secondary outcomes are systolic blood pressure, plasma renin and norepinephrine.

The registry gives a start date of 2018-06-30 and primary completion date of 2020-12-01. It reports 0 serious events, 0 other events and 0 deaths in each group, with 11 participants at risk per group. Allocation is not stated; the record notes that the comparison is not randomized and that the arms are not a like-for-like control comparison.

Outcome estimates and statistical analyses are not reported in the registry record. Consequently, the primary and secondary results, their precision and the methods used to analyze them cannot be assessed from the posted record.