Computer-Aided Prevention System: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Computer-Aided Prevention System (NCT02444715), a randomized na study. The primary outcome is Change in Systolic Blood Pressure.

2. Clinical Question

3. Trial Design

The Computer-Aided Prevention System study (NCT02444715) is recorded as a randomized, parallel-group trial with no masking. Its status is completed, and the registry lists enrollment of 94. The study start is recorded as 2013-01 and primary completion as 2014-08. The phase is listed as NA. The sponsor is Lübomira Spassova.

The intervention was CAPSYS, a computer-based lifestyle coaching system, and the comparator was standard care. The study description frames the system as support for behavior changes related to individual risk factors. It describes telephone access, questions about lifestyle and blood pressure, and personalized verbal feedback. The registry record does not specify the content of standard care or give detailed arm descriptions, and does not report the allocation procedure beyond identifying the study as randomized.

The primary endpoint was change in systolic blood pressure, measured in mmHg, from baseline to 6 months. For the posted endpoint summaries, 32 standard-care participants and 28 interventional-care participants are included. The endpoint description notes that blood pressure data are missing for 4 of the 36 standard-care participants and 4 of the 32 interventional-care participants who provided final questionnaires.

The registry lists five secondary outcomes: changes in fruit and vegetable consumption, whole-grain food consumption, sweets consumption, duration of physical activity, and quality of life. It records 13 outcome measures and 26 analyses overall. The registry record does not report a protocol, allocation concealment, the original sample-size justification, or a detailed analysis plan. Those omissions limit how fully the design and analysis choices can be assessed.

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: Blood pressure data is missing for 4 of the 36 SC and 4 of the 32 IC participants who provided final questionnaires.

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 Change in Systolic Blood Pressure, measured over baseline and 6 months.

Systolic blood pressure is the pressure in the arteries when the heart contracts. The primary endpoint is its change from baseline to 6 months, expressed in mmHg. The posted endpoint is a continuous measure summarized by a mean and standard deviation. In a trial comparing two groups, the central statistical question is whether the average change differs between groups, rather than whether one group changed significantly when considered alone.

Blood pressure is relevant to the study’s stated focus on cerebrovascular and cardiovascular risk factors. The study description presents CAPSYS as a tool for supporting lifestyle changes, and the endpoint captures one measurable risk factor over the stated follow-up period. That rationale does not establish that a change in this measure necessarily produces a change in clinical events; the posted primary endpoint is blood pressure change, not stroke or another clinical event.

The registry record reports a mean change of 0.19 mmHg in standard care and -9.0 mmHg in interventional care. Negative change indicates a lower value at follow-up than at baseline if change is defined as follow-up minus baseline, but the registry does not state the calculation convention in the endpoint description. The unadjusted between-group estimate is reported as -9.19 mmHg for interventional care relative to standard care. The endpoint description also reports missing blood pressure data among participants who completed final questionnaires, so the endpoint summaries do not include all those questionnaire respondents.

7. Results Posted in the Registry

• Interventional Care (IC): mean -9.00 versus 0.19 on control; difference -9.19 (95% CI -20.02 to 1.64), standardized effect d = -0.43; z-test p = 0.096.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary endpoint is continuous: systolic blood pressure change is summarized as a mean and standard deviation. A mean describes the average observed change in a group, while a standard deviation describes how spread out individual measurements are around that mean. These summaries are useful for comparing groups, but do not show the full distribution of participant-level changes.

What does the between-group estimate represent?

The unadjusted mean difference is the interventional-care mean change minus the standard-care mean change. It is reported as -9.19 mmHg. A negative value means the interventional-care mean is lower than the standard-care mean under that comparison direction. This is a contrast between group averages, not a measure of the change experienced by every participant. It also does not adjust for baseline variables or other factors.

The recalculation uses the posted group summaries: means of 0.19 mmHg and -9.0 mmHg, standard deviations of 21.34 and 21.37 mmHg, and group sizes of 32 and 28. These group sizes are the participants represented in the primary endpoint summaries. The calculation is identified as an unadjusted recalculation, not as the sponsor’s own analysis. The registry record does not report the sponsor’s full statistical method for the primary endpoint or enough detail to reproduce a sponsor-reported between-group estimate.

How should a p-value be understood?

A p-value describes how incompatible the observed data are with a specified null hypothesis, assuming the statistical model and its assumptions apply. It is not the probability that the null hypothesis is true, nor does it measure the clinical importance of an estimate. The recalculated p-value of 0.096 relates to the unadjusted between-group comparison. The registry’s p-values of 0.96 and 0.03 are for separate two-sided tests listed for the standard-care and interventional-care groups. These are different questions and should not be substituted for the between-group test.

General statistical principle: a comparison of two within-group p-values is not a valid substitute for directly testing the difference between groups. The apparent pattern of one group’s result crossing a conventional significance threshold and the other not crossing it does not establish that the groups differ. The estimate and its confidence interval are more directly informative about the size and precision of the between-group contrast.

What does a confidence interval add?

A confidence interval gives a range of estimates compatible with the observed data under the method’s assumptions. The 95% interval for the recalculated mean difference is -20.02 to 1.642 mmHg. It includes zero, which corresponds to no mean difference. It also includes values on both sides of zero, so the estimate is not precise enough to establish a single direction of the group contrast. A confidence interval is not a range containing 95% of individual participant outcomes, and it does not account for uncertainties that were not included in the calculation.

What is meant by an unadjusted analysis?

An unadjusted comparison uses the outcome summaries without accounting for additional covariates. General statistical principle: adjustment can be useful when the analysis plan specifies relevant baseline variables, but the appropriate model depends on the design and data. The registry record does not report whether the sponsor used an adjusted model for this endpoint, which covariates might have been included, or how the endpoint change was calculated. The unadjusted calculation should therefore be read as a straightforward summary-based contrast, not as a reconstruction of an undisclosed sponsor model.

Why might variability matter?

The reported standard deviations, 21.34 mmHg and 21.37 mmHg, are large relative to the difference in group means. General statistical principle: greater variation among participant outcomes makes it harder to estimate a group mean or difference precisely, unless the study has enough observations to offset that variation. When data are more variable than a model assumes, standard errors and confidence intervals can be unreliable. Over-dispersion is a general concern when observed variation exceeds what an assumed model allows; the registry record does not report a model assessment or identify over-dispersion in this trial.

The endpoint summaries are based on 32 standard-care and 28 interventional-care participants. The description notes missing blood pressure values for 4 participants in each group among those who provided final questionnaires. The registry record does not explain whether missing values were excluded, imputed, or otherwise handled in the sponsor’s analysis. The available recalculation uses the posted summaries and cannot account for unobserved outcomes or establish whether missingness affected the comparison.

Overall, the statistical interpretation should keep three items distinct: the within-group tests reported by the registry, the unadjusted between-group recalculation, and the sponsor’s own analysis. Because the record marks a discrepancy, the sponsor’s analysis takes precedence as the sponsor-reported result. The recalculation remains a transparent summary-based comparison, but it should not be presented as the study’s original analysis plan or as an adjusted treatment-effect estimate.

10. Confidence Intervals and Precision

The unadjusted mean difference in systolic blood pressure change is -9.19 mmHg, with a 95% confidence interval from -20.02 to 1.642 mmHg. This interval is wide enough to include zero as well as values indicating a difference in either direction. It therefore communicates substantial uncertainty about the size and direction of the between-group contrast. The estimate is not precise enough to support a narrow claim about the average difference.

In general, a confidence interval describes the range of values compatible with the data under the calculation’s assumptions. It is not a guarantee that the true value lies inside the interval, and it does not describe the range of outcomes among individual participants. Here, the interval is for the unadjusted difference in group means, not for individual blood pressure changes.

The group standard deviations are 21.34 mmHg in standard care and 21.37 mmHg in interventional care. The endpoint comparison includes 32 and 28 participants, respectively. General statistical principle: estimates tend to be less precise when participant outcomes vary substantially or when group sizes are limited. The registry record does not report additional analysis details that could clarify how the sponsor accounted for variation or missing outcome data.

The interval is associated with the recalculation, not a sponsor-reported confidence interval. The sponsor’s own analysis takes precedence because the registry record marks a discrepancy. The record does not report a sponsor confidence interval for a direct between-group effect, so the precision of that sponsor-reported contrast cannot be assessed from the posted information.

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. They illustrate the approximate group size associated with different target power levels under the stated planning assumptions. The assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set to a stated fraction of the observed effect. The original trial’s own sample-size assumptions and justification are not reported in the registry record.

For planning for 100% of the observed effect, the illustration gives 85 participants per arm for 80% power and 114 participants per arm for 90% power. For planning for 75% of the observed effect, it gives 151 participants per arm for 80% power and 202 participants per arm for 90% power. For planning for 50% of the observed effect, it gives 340 participants per arm for 80% power and 454 participants per arm for 90% power.

In plain terms, 80% power means that, under the planning assumptions and if the specified effect were the true effect, the design would have an 80% chance of detecting that effect at the chosen significance level. The 90% column uses the same idea with a higher chance of detection. Smaller target effects require more participants per arm because they are harder to distinguish from random variation. These are prospective planning illustrations based on the observed effect, not observed power for the completed trial.

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 = -9.190; pooled standard deviation σ = 21.354.
2. n = 2 × (1.96 + 0.842)² × 21.354² / -9.190² = 84.8, rounded up to 85 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 <- -9.19                      # observed difference in means
sigma <- 21.3539707605255                     # 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(2444715)
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 = 85 (80% power), 114 (90% power)
 75% of observed effect: n per arm = 151 (80% power), 202 (90% power)
 50% of observed effect: n per arm = 340 (80% power), 454 (90% power)
power.t.test: 85.7 
Simulated power at n = 85 per arm: 0.793 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Analyses Reported by the Sponsor

The registry lists two sponsor-reported, two-sided t-tests: p = 0.96 for standard care and p = 0.03 for interventional care. They appear as separate group analyses. The registry does not report an estimate, confidence interval, or p-value for the sponsor’s direct comparison of interventional care with standard care in the information available for this analysis.

The recalculation instead compares the posted group means directly. It gives an unadjusted mean difference of -9.19 mmHg, a 95% confidence interval from -20.02 to 1.642 mmHg, and p = 0.096. These results address the between-group contrast and should not be equated with the sponsor’s within-group tests. The difference between a statistically significant within-group result and a non-significant within-group result does not itself demonstrate a statistically significant between-group difference.

The registry record marks a discrepancy between the sponsor-reported analyses and the recalculation. Accordingly, the sponsor’s own analysis takes precedence when stating the sponsor-reported result. The recalculation is useful as an independent, unadjusted reading of the posted summary statistics, but it is not a replacement for the sponsor’s analysis and does not reveal the sponsor’s full model or analysis population. Details of the sponsor’s endpoint calculation and any adjustments are not reported in the registry record.

14. Multiplicity, Missing Data and Analysis Populations

The registry record lists 13 outcome measures and 26 analyses. It identifies five secondary outcomes: changes in fruit and vegetable consumption, whole-grain food consumption, sweets consumption, duration of physical activity, and quality of life. With multiple outcomes or analyses, the chance of at least one apparently unusual result can increase if each is tested separately. General statistical principle: multiplicity procedures can control specified error rates, but the appropriate approach depends on which outcomes and comparisons were planned.

Whether the study used a multiplicity adjustment, a hierarchy of endpoints, or a prespecified strategy for interpreting multiple tests is not reported in the registry record. The record also does not report a protocol or statistical analysis plan that would establish which analyses were prespecified. Therefore, the posted p-values should not be assumed to have been adjusted for the full set of outcomes and analyses.

For the primary endpoint, blood pressure data are missing for 4 of the 36 standard-care participants and 4 of the 32 interventional-care participants who provided final questionnaires. The posted endpoint summaries include 32 and 28 participants, respectively. The record does not report why those blood pressure measurements are missing, whether missingness was related to participant characteristics or outcomes, or how the sponsor handled missing data in its analysis. It does not report whether an imputation method, a sensitivity analysis, or another approach was used.

The registry record does not identify an intention-to-treat, per-protocol, or other named analysis population for the primary endpoint. It is therefore not possible to determine from the posted information whether all randomized participants were included in the sponsor’s primary analysis or how deviations from assigned care were treated. The record also does not report adherence to CAPSYS or the extent of participant exposure to the coaching system. These omissions matter because the analyzed group and missing-data approach can affect the meaning of an estimated group contrast.

15. 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 0 serious adverse events among 46 participants at risk in standard care and 0 among 48 participants at risk in interventional care. It also lists 0 other adverse events among 46 standard-care participants at risk and 0 among 48 interventional-care participants at risk. These safety denominators differ from the endpoint analysis group sizes of 32 and 28, so the efficacy and safety summaries should not be assumed to use the same participants.

The registry does not list serious adverse-event terms. Death counts are not reported in the registry record. Zero reported events in these summaries means none were recorded in the listed categories for the stated at-risk groups; it does not establish that no events occurred outside the recorded categories or observation period. The record does not provide enough detail about safety surveillance, event definitions, follow-up duration, or attribution to compare the completeness of reporting across groups.

These figures are descriptive counts, not a formal comparison of safety risks. With no serious or other adverse events listed, the posted counts do not quantify how well the study could detect differences in uncommon events. The registry safety entries should therefore be read narrowly as the reported event counts and denominators, without extending them beyond the information recorded.

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

The primary endpoint concerns average change in systolic blood pressure over the period from baseline to 6 months. The posted means are 0.19 mmHg for standard care and -9.0 mmHg for interventional care. The summary-based, unadjusted between-group estimate is -9.19 mmHg. Its confidence interval, -20.02 to 1.642 mmHg, includes zero and spans values on both sides of no difference. Thus, the recalculation does not provide a precise estimate of the between-group contrast.

This does not mean that the groups are known to be identical, nor does it prove that the intervention has no effect. It means the available summary-based analysis remains compatible with more than one interpretation of the average difference. The estimate’s point direction favors a larger reduction in interventional care, but the interval indicates uncertainty about both magnitude and direction. The registry’s separate within-group p-values do not resolve this uncertainty about the direct group comparison.

The results are limited to systolic blood pressure change in the reported analysis groups. They do not show whether CAPSYS changed stroke incidence, cardiovascular events, or longer-term health outcomes. The study description presents lifestyle coaching as a way to support behavior changes, but the primary endpoint is not a direct measure of all those behaviors or of clinical events.

The trial is recorded as randomized, which is a design feature intended to support a fair comparison between groups. However, the registry does not report detailed randomization procedures, missing-data methods, analysis populations, or the sponsor’s full primary endpoint analysis. The endpoint description notes missing blood pressure data among final-questionnaire respondents. Those gaps limit assessment of possible bias and the robustness of the reported comparison.

The sponsor-reported results and the unadjusted recalculation answer different statistical questions in the posted information. Because a discrepancy is recorded, the sponsor’s own analysis takes precedence as the sponsor-reported result. The recalculation is informative as a direct contrast of the available group summaries, but it should not be mistaken for the trial’s original prespecified analysis or interpreted as definitive evidence of a clinical benefit or lack of benefit.

17. Why This Trial Matters Statistically

This study illustrates why the choice of statistical contrast matters. A trial with two groups is usually interpreted through the difference between groups, while a test within each group asks whether that group’s change differs from a reference value. The registry reports separate within-group tests, but the clinically relevant statistical contrast for the primary endpoint is the difference in mean change between interventional care and standard care. Those are not interchangeable questions.

It also shows why estimates and confidence intervals should be read alongside p-values. The unadjusted estimate is -9.19 mmHg, but its 95% confidence interval extends from -20.02 to 1.642 mmHg. The interval conveys uncertainty about the possible size and direction of the group contrast. A single p-value cannot describe that range of plausible estimates or communicate the degree of imprecision as directly.

Missing outcome data are another important part of the statistical interpretation. Blood pressure data were missing for 4 participants in each group among those who submitted final questionnaires, and the posted endpoint groups are smaller than those questionnaire groups. Without the sponsor’s missing-data approach or analysis-population definition, readers cannot fully evaluate whether the reported summaries represent all randomized participants or how the missing measurements may have affected the estimate.

Finally, the record lists multiple outcomes and analyses but does not report a multiplicity strategy. This leaves uncertainty about how the collection of tests was intended to be interpreted. Taken together, the trial is a useful example of the need to separate endpoint choice, direct between-group inference, missing-data handling, and multiplicity from the simple presence or absence of a within-group p-value below a conventional threshold.

18. Limitations

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

The registry record contains limited detail about the trial procedures and analysis. It identifies randomization, no masking, and a parallel design, but does not report the sequence-generation method, allocation concealment, or practical details about how participants were assigned. Arm descriptions beyond the names of standard care and interventional care are empty. The content of standard care is therefore not specified, which limits interpretation of the contrast.

The record does not report participant characteristics, eligibility criteria, adherence to CAPSYS, or how often participants used the system. It also does not provide the original sample-size justification, a protocol, or a statistical analysis plan. The planning illustrations use the observed effect and are not evidence of the original design assumptions.

For the primary endpoint, blood pressure measurements were missing for 4 of the 36 standard-care and 4 of the 32 interventional-care participants who provided final questionnaires. The registry does not explain the reasons for missingness or the method used to address it. The primary endpoint summaries include 32 and 28 participants, but the analysis population is not named. This makes it difficult to assess whether missing data or exclusions may have influenced the comparison.

The registry lists separate within-group tests and does not provide the sponsor’s direct between-group estimate in the information available for this analysis. The summary-based recalculation is unadjusted, and the record marks a discrepancy, so the sponsor’s own analysis takes precedence. The record also lists 13 outcome measures and 26 analyses without reporting whether multiplicity was addressed. These limitations constrain interpretation of both the primary comparison and the wider set of findings.

Safety counts use denominators of 46 and 48, distinct from the primary endpoint groups, and death counts are not reported in the registry record. Details of safety follow-up and event ascertainment are also not reported in the registry record.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Computer-Aided Prevention System — NCT02444715.
• Registry record last updated 2016-02-18; status last verified 2016-01.
• Results first posted 2015-08-24.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

22. Record Summary

NCT02444715 is a completed randomized, parallel-group study with no masking and enrollment of 94. It compares CAPSYS interventional care with standard care. The study description presents CAPSYS as a telephone-accessible computer-based lifestyle coaching system that provides personalized verbal feedback. The registry records the study start as 2013-01 and primary completion as 2014-08.

The primary endpoint is change in systolic blood pressure from baseline to 6 months. Posted means are 0.19 mmHg for standard care and -9.0 mmHg for interventional care, with endpoint analysis groups of 32 and 28 participants. The unadjusted recalculated difference is -9.19 mmHg, with a 95% confidence interval of -20.02 to 1.642 mmHg and p = 0.096. The interval includes zero. The registry separately lists within-group p-values of 0.96 and 0.03.

The registry marks a discrepancy, so the sponsor’s own analysis takes precedence. Details of the sponsor’s direct between-group analysis, missing-data methods, multiplicity strategy, and original sample-size justification are not reported in the registry record. The safety summaries list no serious or other adverse events in the stated at-risk groups; death counts are not reported in the registry record.