Benefit of Lumbar Bracing for Chronic Low Back Pain Due to Degenerative Disc Disease: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Benefit of Lumbar Bracing for Chronic Low Back Pain Due to Degenerative Disc Disease (NCT03484403), a randomized na study. The primary outcome is Pain Diary.

2. Clinical Question

3. Trial Design

The registry describes a randomized, parallel-group study with no masking. Its stated enrollment is 61, while the posted primary-outcome groups are listed as 34 in the control group and 25 in the treatment group. These are the group sizes attached to the posted pain summaries; the record does not explain the relationship between those figures and the enrollment figure.

The control group received back school education and physical therapy exercise instruction. The treatment group received the same education and exercise instruction, with a lumbar support back brace added. This design targets the incremental comparison of bracing alongside the shared care components. It does not isolate the effects of education or exercise, because both groups received them.

The study status is completed. The recorded study start was 2015-12-14, and the primary completion date was 2019-09-10. The registry lists the sponsor as Dallas VA Medical Center. More detailed information about the setting, recruitment, allocation procedures, concealment, and conduct of follow-up is not reported in the registry record.

The primary outcome is a continuous pain measure summarized by group means and standard deviations. The registry lists four outcome measures, but no secondary outcome results are posted. The record also lists no analysis entries. Consequently, the posted summary-statistic comparison can be described, but a fuller account of the trial’s own analysis methods and results is not available 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.

Before assignment: 2 participants withdrew after enrollment

Overall Study

Reasons for not completing this period:

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 Pain Diary, measured over Change between baseline and each week for 6 weeks.

The primary endpoint is the Pain Diary outcome. Participants rated weekly pain on a scale from 0-10; lower values indicate better outcomes. The stated timeframe is change between baseline and each week for 6 weeks. The registry description says average weekly pain scores were compared from baseline to the six-week mark.

A repeated pain rating can describe symptoms over time rather than relying on a single assessment. Comparing pain between groups can address whether the group assigned a brace alongside education and exercise had different reported pain from the group assigned education and exercise alone. This is a general explanation of why a repeated patient-reported measure may be useful; it does not establish how the trial analyzed the sequence of weekly ratings.

The registry does not provide a detailed scoring or aggregation protocol beyond the scale and timeframe. It is therefore unclear whether the posted group means represent pain levels at the six-week assessment, changes from baseline, or another summary of the weekly records. That distinction matters because a level and a change answer different questions. The posted results should be interpreted using the endpoint description as recorded, without assuming an unreported calculation method.

7. Results Posted in the Registry

• Treatment Group: mean 5.00 versus 6.71 on control; difference -1.71 (95% CI -2.58 to -0.84), standardized effect d = -1.03; z-test p = <0.001.

8. Statistical Interpretation

9. Statistical Methods Explained

What does a mean difference describe?

A mean difference expresses the distance between two group averages in the original measurement units. In this registry comparison, the treatment group mean is compared with the control group mean, and the reported difference is -1.71 units on the pain scale. A negative value means the treatment-group mean is lower under that ordering. Since lower pain values are described as better, the direction is favorable to the treatment group in the posted summary. This is a general explanation of a mean difference; it does not establish the source of the difference or its clinical importance.

The mean summarizes the group’s values, but it does not show how each participant’s ratings were distributed, whether changes varied over time, or whether a small number of observations influenced the average. The standard deviations posted for the groups, 1.56 and 1.78, describe variability of observations around their respective means. They are not confidence limits and do not show the uncertainty in the difference by themselves.

What does the unadjusted comparison mean?

The posted comparison is an unadjusted calculation from the group summary statistics. It does not account for baseline values or other participant characteristics in a regression model. The registry lists no analysis entries, so it does not provide a reported trial model to compare against this summary calculation. The unadjusted p-value is <0.001. In general, a p-value measures how unusual data at least as discrepant as the observed data would be under a specified null hypothesis and analysis procedure. It is not the probability that the null hypothesis is true, and it does not measure the size or importance of an effect.

The calculation’s interpretation also depends on the outcome being compared. The record describes ratings over time and mentions change from baseline, but does not specify clearly whether the posted means are endpoint pain levels or changes. A summary comparison at one endpoint is not interchangeable with an analysis of repeated weekly ratings or a comparison of change scores.

Why does a confidence interval matter?

A confidence interval gives a range of values compatible with the observed data under the method used. In general, a narrower interval indicates greater statistical precision, while a wider interval leaves more uncertainty about the size of the difference. The interval posted for this comparison runs from -2.583 to -0.837. Its bounds are both negative, indicating that the range of differences compatible with this calculation is below zero. The interval is not a guarantee that the true effect falls within those bounds, nor does it include uncertainty from design or reporting limitations that the calculation does not model.

The confidence interval and p-value are related summaries of the same comparison, not independent confirmations. Their interpretation relies on the method and assumptions used to calculate them. The record does not describe a trial-specific statistical model, adjustment strategy, or handling of repeated measures. General statistical concepts can explain what these summaries mean, but cannot fill in those unreported methods.

What does standardized effect size add?

The posted standardized mean difference is -1.032. Standardizing expresses a mean difference relative to variability, which can help describe magnitude without using the original scale units. It is less directly interpretable than the difference in pain-scale units, and its value depends on the variability estimate used. It does not replace the original-unit result, resolve the endpoint-description ambiguity, or establish clinical importance. The registry does not state a threshold for a clinically meaningful change.

Why can variability matter?

In general, greater variability makes group averages less precise when other features of the design are held constant. The posted standard deviations are not identical between the groups. The comparison uses a pooled standard deviation of 1.656, as listed in the registry-derived statistics. A pooled estimate combines group variability for a standardized comparison; it does not mean the groups have identical distributions. The calculation is described as using the posted summary statistics, and the record does not report a separate variance model.

These methods explain the summaries, but they do not substitute for the missing trial analysis details. In particular, the record does not report how missing weekly ratings were handled, whether all randomized participants were included in the primary analysis, or whether any prespecified analysis was adjusted for baseline pain. Those details would be needed to understand how the trial team intended to estimate the primary comparison.

10. Confidence Intervals and Precision

The mean difference is -1.71, with a confidence interval from -2.583 to -0.837. The interval is entirely below zero and does not cross the no-difference value. Under the unadjusted calculation, the values most compatible with the observed data therefore indicate a lower mean pain value in the treatment group than in the control group. The direction is interpreted using the registry’s statement that lower pain values indicate better outcomes.

The interval still spans a range of possible difference sizes. Its lower and upper bounds do not identify a single exact effect, and the point estimate should not be treated as known without uncertainty. In general, confidence intervals describe sampling uncertainty under the calculation’s assumptions. They do not capture every source of uncertainty, such as unclear outcome construction, missing-data decisions, or limitations in trial conduct that are not represented in the summary calculation.

The unadjusted p-value is <0.001. That indicates that the observed summary comparison is not readily explained by sampling variation alone under the null model and calculation used. It does not indicate the probability that the treatment has a particular effect, nor does it establish clinical importance. The registry does not report a clinically important difference threshold for this pain measure.

Interpretation of precision is also affected by the outcome description. The registry refers to change between baseline and each week, while its description of the comparison refers to average weekly pain scores from baseline to the six-week mark. Without a clearer definition, the interval’s numerical precision can be described, but the precise estimand represented by the interval remains uncertain. The registry does not report a trial-specific confidence-interval method or adjusted model.

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 event counts. They are illustrations based on the observed effect, rather than the original trial’s design assumptions. The planning method uses a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. It considers effects defined as 100%, 75%, and 50% of the observed effect.

For planning at 100% of the observed effect, the figures are 15 participants per arm for 80% power and 20 participants per arm for 90% power. At 75% of the observed effect, the corresponding figures are 27 and 36 participants per arm. At 50% of the observed effect, they are 59 and 79 participants per arm.

In plain terms, the 80% power column describes the planned number per arm for a design with an 80% chance of detecting the specified effect under the stated assumptions, if that effect is real and the assumptions hold. The 90% power column describes the corresponding planning target for a 90% chance. These are design calculations, not guarantees about results.

Smaller effects are harder to distinguish from random variation, so planning for a smaller fraction of the observed effect requires more participants per arm. These figures are not observed power and do not show the probability that the completed study detected its effect. The registry does not report the trial’s original sample-size justification or its original design assumptions.

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 = -1.710; pooled standard deviation σ = 1.656.
2. n = 2 × (1.96 + 0.842)² × 1.656² / -1.710² = 14.7, rounded up to 15 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 <- -1.71                      # observed difference in means
sigma <- 1.65619729310376                     # 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(3484403)
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 = 15 (80% power), 20 (90% power)
 75% of observed effect: n per arm = 27 (80% power), 36 (90% power)
 50% of observed effect: n per arm = 59 (80% power), 79 (90% power)
power.t.test: 15.7 
Simulated power at n = 15 per arm: 0.782 (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 four outcome measures, but no secondary outcome results are posted. The primary outcome is the Pain Diary measure. The record does not report whether the study prespecified a hierarchy of outcomes, how it handled multiple comparisons, or whether any multiplicity adjustment was planned or performed. Without those details, the posted unadjusted p-value should be read as a result for the reported comparison, not as evidence that a family of outcomes was controlled for multiple testing.

The record lists no analysis entries. It does not describe the analysis population, such as whether the primary comparison included all randomized participants, only participants with available outcome data, or another group. It also does not report whether the main analysis followed the assigned groups regardless of adherence. These are important distinctions when interpreting a randomized comparison because the analysis population and treatment of adherence can affect the estimand.

Missing-data methods are not reported in the registry record. The pain measure is described as weekly ratings over 6 weeks, but the record does not state how missed diaries, incomplete follow-up, or other absent observations were handled. It also does not say whether any imputation, sensitivity analysis, or complete-case approach was used. If missingness differs between groups or relates to pain, results based only on available ratings may not represent the same comparison as a complete follow-up analysis.

The record does not report a repeated-measures model or explain how multiple weekly ratings were incorporated into the primary comparison. It therefore cannot establish whether the estimate used all weekly data, a single endpoint, or a summary derived from the weekly scores. These omissions do not invalidate the posted arithmetic comparison, but they limit conclusions about the trial’s prespecified analysis and the robustness of its result.

14. 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 serious adverse events for 0 of 34 participants at risk in the control group and 0 of 25 participants at risk in the treatment group. It also lists other adverse events for 0 of 34 participants at risk in the control group and 0 of 25 participants at risk in the treatment group. Deaths are listed as 0 in each group. These are the event counts recorded in the registry, not proof that no adverse experiences occurred.

Zero recorded events in these groups means the posted record contains no events of those categories for the listed groups. It does not show how adverse events were defined, how actively they were collected, or whether follow-up was complete for safety reporting. The registry does not provide event descriptions for these categories, and no serious adverse event terms are listed.

Safety counts should be read alongside the group sizes at risk and the reporting period, but the record does not detail the safety observation window or ascertainment procedures. The figures cannot establish that an event is impossible or rule out uncommon events. They describe only what was recorded in this registry entry.

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

The posted primary comparison shows lower mean pain in the treatment group than in the control group: the means are 5.0 and 6.71, respectively, and the reported mean difference is -1.71. The confidence interval from -2.583 to -0.837 remains below zero, and the unadjusted p-value is <0.001. These statistics describe the posted comparison, with lower values defined as better on the pain scale.

The result does not by itself establish that the brace caused the difference. Although the study is described as randomized, the registry does not provide enough detail to assess the allocation process, analysis population, missing-data handling, or the trial’s statistical plan. The displayed comparison is an unadjusted calculation from group summaries, not a reported adjusted analysis. It should not be treated as a substitute for a complete account of the trial’s own analysis.

The result also does not establish the benefit of a brace without other care. Both groups received back school education and the same physical therapy exercise instruction; the contrast adds a lumbar brace to those shared components. The result therefore addresses that particular combination and comparator.

The clinical meaning remains uncertain because the registry does not state a threshold for a clinically important difference. It also does not make fully clear whether the posted means represent endpoint pain levels or changes from baseline. No secondary outcome results are posted, including results for the stated adherence aim. The reported pain comparison is informative as a numerical summary, but it does not answer every question raised by the study objectives.

16. Why This Trial Matters Statistically

This trial’s comparison is statistically useful because the groups shared back school education and physical therapy exercise instruction, while the treatment group also received a lumbar brace. That structure focuses the comparison on the addition of bracing within the care program described in the registry. It is important to distinguish this question from whether bracing alone changes pain or whether education and exercise are effective.

The outcome is patient-reported pain recorded weekly on a 0-10 scale. Repeated symptom ratings can capture how an experience varies over time, but the registry’s description does not specify precisely how the weekly records were reduced to the displayed group summaries. That uncertainty illustrates why clear endpoint definitions and analysis descriptions matter: the same scale can support different estimands depending on whether investigators compare final levels, changes, or a summary across visits.

The mean difference and confidence interval give complementary information. The point estimate describes the observed separation in scale units, while the interval conveys uncertainty around that estimate under the calculation used. Their interpretation is stronger when paired with clear outcome definitions, analysis populations, and missing-data methods. Those details are not reported in the registry record.

The registry also states an adherence objective, but no adherence result is posted. This separates the question of assignment to a brace from the question of whether participants followed wear instructions. Without adherence information and secondary results, the posted pain comparison cannot explain how use of the brace related to outcome variation.

More broadly, the record demonstrates why statistical evidence should be read together with design and reporting details. A small p-value does not resolve questions about endpoint construction, clinical importance, or generalizability. The numerical result is one part of the evidence, not a complete account of what the study establishes.

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 identifies the population broadly as people with chronic low back pain related to degenerative disc disease, and the study aims specify uncomplicated cases without radiculopathy or neurogenic claudication. Detailed inclusion and exclusion criteria, participant characteristics, and the setting of recruitment are not reported in the registry record. The extent to which the posted result applies to people outside the described group cannot be determined from the available details.

The primary outcome description is ambiguous. It gives a timeframe of change between baseline and each week for 6 weeks, but also states that average weekly pain scores were compared from baseline to the six-week mark. The record does not clarify whether the displayed means are pain levels, changes, or another summary. This limits the precision of the substantive interpretation.

The registry does not report how randomization was generated or concealed, whether the outcome assessor was masked, or how protocol deviations were handled. It lists no analysis entries and does not report a statistical plan, analysis population, missing-data method, or a model for repeated measurements. These omissions prevent assessment of whether the posted summary comparison reflects the intended primary analysis.

The record lists four outcome measures but posts no secondary outcome results, including the stated adherence objective. It also does not report a clinically important difference threshold. The adverse-event record lists zero events in the posted categories, but details of safety collection and follow-up are not reported. Finally, the registry does not report the study’s original sample-size justification or design assumptions, so the planning illustrations should not be taken as evidence of the trial’s original planning process.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Benefit of Lumbar Bracing for Chronic Low Back Pain Due to Degenerative Disc Disease — NCT03484403.
• Registry record last updated 2024-01-08; status last verified 2023-04.
• Results first posted 2024-01-08.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

21. Record Summary

The registry describes a completed, randomized, parallel-group study without masking. The treatment group received a lumbar back brace, back school education, and physical therapy exercise instruction; the control group received the education and exercise instruction without a brace. The stated enrollment is 61.

The primary outcome was weekly Pain Diary ratings on a 0-10 scale, with lower values indicating better outcomes. The posted group means are 5.0 for the treatment group and 6.71 for the control group. The unadjusted mean difference is -1.71, with a confidence interval from -2.583 to -0.837 and p < 0.001.

The registry does not report a detailed statistical plan, analysis population, missing-data approach, or a clear definition of whether the posted means are endpoint levels or changes. No secondary outcome results are posted. The registry lists zero serious adverse events, zero other adverse events, and zero deaths in each group.