Mindfulness Based Stress Reduction for High Blood Pressure: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Mindfulness Based Stress Reduction for High Blood Pressure (NCT00440596), a randomized na study. The primary outcome is SBP.

2. Clinical Question

3. Trial Design

The registry identifies this as a randomized, single-masked trial with a factorial model. It lists mindfulness-based stress reduction and progressive muscle relaxation as the behavioral interventions, and gives an enrollment of 56. The study status is completed. The start date is recorded as 2006-09 and primary completion as 2009-07. Kent State University is listed as the sponsor.

The registry description characterizes the study as a feasibility randomized clinical trial of MBSR for unmedicated prehypertension. It states that the aims included assessing feasibility and safety, and documenting any treatment effect, as preliminary evidence for a possible larger trial. Those stated aims provide context for interpreting the outcome: this was not described as a definitive effectiveness trial.

The primary outcome population is recorded as 56 participants on an intent-to-treat basis. The endpoint was mean systolic blood pressure in mm Hg at 12 weeks. The posted group results list 28 participants for MBSR and 28 for progressive muscle relaxation. The registry record does not report who was masked, how the factorial model was implemented, or the details of the randomization procedure. It also does not report the trial’s original sample-size assumptions or a fuller statistical analysis plan.

The registry lists two outcome measures and no posted secondary results. The study description gives background about elevated blood pressure and lifestyle modification, but the endpoint comparison is between MBSR and progressive muscle relaxation. No separate result comparing either intervention with usual care or no intervention is reported.

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.

Before assignment: 181 did not meet inclusion criteria 11 did not consent to participate

Overall Study

Analysis population for the primary outcome, as defined in the registry: 56 participatns intent to treat

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 SBP, measured over 12 weeks.

The primary endpoint is systolic blood pressure (SBP), measured in mm Hg, reported as a group mean at 12 weeks. SBP is the pressure recorded during heart contraction; it is one component of a blood-pressure reading. The registry identifies the outcome as a continuous measure and reports a standard deviation for each group.

A group mean describes the average endpoint value among the participants included in that group’s outcome summary. The standard deviation describes variation among individual measurements around that average. It is not the same as the uncertainty around the estimated group mean or the between-group difference.

Comparing the groups’ means addresses whether their average SBP values differed at the stated follow-up. The posted means are 130.2 mm Hg for MBSR and 128.8 mm Hg for progressive muscle relaxation. The registry reports a mean difference of -1.4 mm Hg, with a confidence interval from -4.7 to 1.9. The registry record does not describe the measurement equipment, measurement schedule within the 12-week visit, or rules for summarizing repeated readings. Those details can affect how an endpoint is collected, but they are not reported in the registry record.

7. Results Posted in the Registry

• Progressive Muscle Relaxation: mean 128.80 versus 130.20 on control; difference -1.40 (95% CI -4.70 to 1.90), standardized effect d = -0.22; z-test p = 0.406.

8. Statistical Interpretation

9. Statistical Methods Explained

The posted endpoint is a continuous measurement summarized by a mean and standard deviation. A mean is the arithmetic average of measurements in a group. The standard deviation describes how dispersed individual measurements are around that group average. These summaries answer different questions: the mean describes the group’s central value, while the standard deviation describes participant-level variability. Neither standard deviation alone gives the uncertainty in the estimated difference between group means.

What does the mean difference represent?

A mean difference compares the average endpoint values in two groups. In this trial, the registry reports means of 130.2 mm Hg for MBSR and 128.8 mm Hg for progressive muscle relaxation, and gives the mean-difference estimate as -1.4 mm Hg. The sign of a difference depends on the order in which groups are subtracted. The registry record lists the comparison estimate but does not provide a fuller verbal definition of its subtraction convention, so the reported estimate is best quoted as recorded rather than reinterpreted.

A mean difference is expressed in the endpoint’s original unit, which is mm Hg. It is therefore directly interpretable on the measurement scale. The registry also provides a standardized estimate, but interpretation of that statistic requires care and does not replace the original-unit estimate. No standardized estimate is needed to understand the reported group means or their confidence interval.

What does the standard deviation tell the reader?

The standard deviation is a description of spread among observations, not an interval around the mean. Both groups have a posted standard deviation of 6.3 mm Hg. Similar reported spread does not prove that the full distributions are identical, nor does it reveal whether measurements were skewed or whether there were outliers. Individual-level data and distributional diagnostics are not reported in the registry record.

For a mean comparison, the uncertainty in the estimated difference depends on the variability of measurements and the amount of information in each group. The posted standard errors for the group means are 1.191. A standard error describes sampling uncertainty in an estimate under the model used; it is not a measure of how much participants differ from one another. The registry does not describe the estimation method in enough detail to independently assess its assumptions.

How should the confidence interval be understood?

A confidence interval gives a range of estimates compatible with the observed data under a statistical procedure and its assumptions. In general, an interval’s width reflects precision: narrower intervals indicate greater precision, and wider intervals indicate less. The interval reported for the mean difference runs from -4.7 to 1.9. Because it includes zero, the posted data do not rule out a zero difference under the interval procedure. The registry record does not state the confidence level, so no confidence percentage should be inferred.

A confidence interval is not a range containing a known proportion of individual participants’ outcomes. It concerns the estimated group contrast. It also does not capture every source of uncertainty, such as uncertainty from study conduct, outcome measurement, or analysis decisions that are not described in the registry.

What does the p-value add?

The registry reports an unadjusted p-value of 0.406. In general, a p-value measures the compatibility of the observed data with a null hypothesis under a specified statistical model. It does not measure the size or clinical importance of a difference, and it does not provide the probability that the null hypothesis is true. The estimate and confidence interval are useful alongside the p-value because they show the direction and range of the reported contrast.

The record labels the p-value unadjusted. The registry record does not report whether other analyses were conducted but omitted, whether the endpoint was selected from multiple planned comparisons, or whether any multiplicity adjustment was planned. As a result, the p-value should be interpreted as the posted unadjusted result, not as evidence that all analysis choices are known.

What does randomization contribute?

Random allocation is intended to make treatment groups comparable on average with respect to factors measured and unmeasured at baseline. It supports a causal interpretation when the trial is conducted and analyzed appropriately, but it does not guarantee balance in a small study. The record identifies randomized allocation, but does not report sequence generation, allocation concealment, baseline characteristics, or the details of the analysis population beyond the intent-to-treat label attached to the primary outcome.

The registry labels the model factorial, but the posted arm descriptions identify MBSR and progressive muscle relaxation. The record does not report the factorial factors, whether an interaction was assessed, or how that model relates to the displayed comparison. No such design details should be inferred from the label alone.

10. Confidence Intervals and Precision

The posted mean-difference estimate is -1.4 mm Hg, and its confidence interval extends from -4.7 to 1.9. This interval is the main indication of precision for the between-group estimate. Its endpoints lie on opposite sides of zero, so the reported uncertainty includes the possibility of no mean difference as well as differences in either direction, according to the contrast convention.

In general, a confidence interval is a range produced by a statistical procedure to represent uncertainty in an estimate. A narrower interval indicates more precision than a wider interval, all else being equal. The interval does not describe the range of individual SBP readings, and it should not be confused with the group standard deviations, which are 6.3 mm Hg in both arms.

The registry record does not state the confidence level for this interval. It also does not report whether the estimate was adjusted for baseline SBP or other covariates. The interval therefore should be interpreted as posted, without assigning it a confidence percentage or assuming an adjusted analysis. The unadjusted p-value is 0.406, which is consistent with the interval’s inclusion of zero under commonly used interval-test relationships, but the registry’s stated analysis details are limited.

Precision is constrained by the amount of information and variability in the observed data, but the interval alone cannot identify which design or analysis factors contributed to its width. The result offers a preliminary estimate, not a sharply determined treatment contrast. The registry record does not report a threshold for a clinically meaningful SBP difference, so statistical precision cannot be translated into a judgment about clinical importance from the posted information alone.

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 are illustrations based on the observed effect rather than the trial’s original design assumptions. The stated planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each scenario uses the stated fraction of the observed effect as the effect to detect.

For planning around 100% of the observed effect, the figures are 318 participants per arm for 80% power and 426 participants per arm for 90% power. For 75% of the observed effect, they are 566 participants per arm for 80% power and 757 participants per arm for 90% power. For 50% of the observed effect, they are 1,272 participants per arm for 80% power and 1,703 participants per arm for 90% power.

In plain language, the 80% power column gives the planned number per group under which the specified effect would have an 80% chance of being detected by the assumed test, if the planning assumptions and effect were correct. The 90% column describes a higher chance of detection under the same framework, which requires more participants per group. Smaller effects are harder to distinguish from random variation, so the planning figures increase as the assumed effect becomes smaller.

These values are planning illustrations, not observed power. They do not show the probability that the trial result is true or that a treatment has an effect. The registry record does not report the original design assumptions for this trial, so these illustrations should not be read as the sample-size rationale used when the trial was planned.

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 = -1.400; pooled standard deviation σ = 6.300.
2. n = 2 × (1.96 + 0.842)² × 6.300² / -1.400² = 317.9, rounded up to 318 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 <- -1.39999999999998                      # observed difference in means
sigma <- 6.3                     # 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(440596)
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 = 318 (80% power), 426 (90% power)
 75% of observed effect: n per arm = 566 (80% power), 757 (90% power)
 50% of observed effect: n per arm = 1,272 (80% power), 1,703 (90% power)
power.t.test: 318.8 
Simulated power at n = 318 per arm: 0.800 (20000 replicates)

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

13. Multiplicity, Missing Data and Analysis Populations

The registry lists two outcome measures, but no secondary outcome results are posted. It reports one primary endpoint result for SBP at 12 weeks. The registry record does not report a complete list of planned hypotheses, the order of testing, or whether the primary endpoint was selected before the data were examined. Without those details, it is not possible to assess the full multiplicity context for the posted p-value.

Multiplicity arises when several outcomes, time points, subgroups, or comparisons are tested. In general, conducting more tests can increase the chance of at least one apparently notable result even when no corresponding effect exists. Statistical approaches can account for multiplicity, but the registry record does not report whether any were planned or used. The posted p-value is identified as unadjusted and should be treated as such.

The primary outcome population is described as 56 participants on an intent-to-treat basis. The registry record does not report how many participants had an observed 12-week SBP measurement, how missing outcome values were handled, or whether any imputation was used. It does not report reasons for missingness or a sensitivity analysis exploring alternative assumptions. Consequently, the extent to which missing data could affect the posted result cannot be assessed from the record.

The record does not provide a protocol-level definition of the intent-to-treat population, details of exclusions after randomization, or a per-protocol analysis. It also does not report baseline outcome values or adjusted estimates. These omissions limit assessment of analysis populations and potential differences between the posted summary and other possible analyses. They do not establish that any particular analysis was or was not conducted; the relevant information is 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 adverse-event results list 28 participants at risk for serious adverse events in each group, with 0 serious adverse events recorded for MBSR and 0 for progressive muscle relaxation. The posted other-adverse-event counts are also 0 for each group. The registry provides no serious adverse-event terms.

These entries describe what was recorded in the registry; they are not proof that no adverse events occurred outside the reported collection or reporting process. The record does not describe event definitions, surveillance procedures, follow-up completeness, or how events were assessed for relationship to an intervention. It also does not give a death count: the death entries are not reported in the registry record, rather than being stated as zero.

Zero recorded events in this study should be interpreted in the context of a feasibility trial and the posted number at risk, not as a precise estimate of safety for broader populations or longer follow-up. The registry’s safety information is limited to these event counts and does not support conclusions beyond the reported record.

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

The posted results show that at 12 weeks the MBSR group had a mean SBP of 130.2 mm Hg, while the progressive muscle relaxation group had a mean of 128.8 mm Hg. The registry reports a mean difference of -1.4 mm Hg and a confidence interval from -4.7 to 1.9. This is an estimate of the group contrast, accompanied by uncertainty that includes values on both sides of zero. The p-value is 0.406.

The findings do not establish that the interventions are equivalent. A nonzero difference could be compatible with the data, as could no difference, and the record does not give an equivalence margin. Nor do the results establish that either intervention changes SBP, because the posted comparison is between two active behavioral interventions and no baseline-adjusted or within-group change result is reported. The comparison should not be recast as an assessment against no intervention or usual care.

The trial description presents the study as a feasibility effort intended to provide preliminary evidence. The posted SBP result is therefore best understood as an early estimate, with limited precision, rather than a definitive answer. The registry record does not report a threshold for clinical importance, so the estimate cannot be categorized as clinically meaningful or unimportant from these data alone.

The result is specific to the reported 12-week endpoint and the participants included in the posted outcome population. It does not show whether differences continued later, whether participants followed the interventions, or whether the study met its feasibility aims. No secondary results are posted. Safety counts are limited to the event information recorded in the registry and do not establish the absence of risk. Overall, the posted data describe one uncertain mean comparison; they do not support broader claims about effectiveness, equivalence, durability, or safety.

16. Why This Trial Matters Statistically

This trial illustrates why a point estimate should not be read without its uncertainty. The reported mean difference is -1.4 mm Hg, but its confidence interval ranges from -4.7 to 1.9. A reader who considers only the point estimate may overlook how much uncertainty remains about the direction and size of the group contrast. The interval offers a more informative account of precision than a binary reading of the p-value alone.

The registry identifies the study as a feasibility trial and describes preliminary evidence as an aim. In that setting, an estimate can help frame later research questions even when it is not precise enough to resolve the intervention comparison. The planning illustrations make the consequence of effect-size assumptions visible: planning around a smaller fraction of the observed effect calls for more participants per arm under the stated assumptions. Those illustrations are not a substitute for the original protocol’s design rationale, which is not reported in the registry record.

The record also highlights the importance of reporting methods alongside results. Information about the confidence level, missing outcomes, measurement procedures, randomization details, and analysis plan is not reported. Without those details, readers can describe the posted summary statistics, but cannot fully evaluate how the estimates were produced or how robust they may be to alternative analytic choices.

Finally, the two behavioral interventions are the only arms with posted SBP means. The estimate therefore answers a narrow comparative question. It should not be generalized into a claim about either intervention versus no treatment, nor taken as proof of equivalence. Careful distinctions between the question asked, the estimate obtained, and the uncertainty around it are central to 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 gives limited detail about the trial’s conduct and analysis. It identifies randomized allocation, single masking, and a factorial model, but does not report the masking role, randomization sequence, concealment procedures, factorial factors, or whether interactions were examined. These details matter when assessing how the design supports the reported comparison.

The posted endpoint summary is confined to group means and standard deviations at 12 weeks, with a mean-difference estimate and confidence interval. Baseline SBP, changes from baseline, adjusted analyses, and later follow-up results are not reported. The registry record also does not describe how SBP was measured or how multiple readings, if any, were summarized.

The primary population is labeled intent-to-treat, but missing outcome counts, missing-data methods, and sensitivity analyses are not reported. The record does not give the original sample-size rationale, a clinically important difference, a detailed statistical plan, or the confidence level for the reported interval. The p-value is unadjusted, while the full set of planned comparisons and any multiplicity approach are not reported.

The registry describes feasibility and safety as study aims, but specific feasibility outcomes are not posted. Safety information is limited to the recorded adverse-event counts, with no event terms or surveillance details. These limitations constrain interpretation of the estimate and prevent broader conclusions about the conduct, completeness, or generalizability of the study.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Mindfulness Based Stress Reduction for High Blood Pressure — NCT00440596.
• Registry record last updated 2020-11-09; status last verified 2020-11.
• Results first posted 2020-11-09.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

21. Record Summary

NCT00440596, titled Mindfulness Based Stress Reduction for High Blood Pressure, is listed as a completed randomized, single-masked trial with a factorial model. Kent State University is the sponsor. The registry records enrollment of 56, a start date of 2006-09, and primary completion in 2009-07.

The posted primary outcome is mean SBP in mm Hg at 12 weeks, for a population described as 56 participants on an intent-to-treat basis. The reported means are 130.2 for MBSR and 128.8 for progressive muscle relaxation. The reported mean difference is -1.4, with a confidence interval from -4.7 to 1.9 and an unadjusted p-value of 0.406.

The registry describes the study as a feasibility trial intended to provide preliminary evidence. No secondary outcome results are posted. The record does not report the original sample-size assumptions, missing-data methods, confidence level, or a full statistical analysis plan.