Efficacy of Foot Orthotics in Veterans With Chronic Lower Back Pain: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Efficacy of Foot Orthotics in Veterans With Chronic Lower Back Pain (NCT01865539), a randomized na study. The primary outcome is Visual Analog Scale (VAS).

2. Clinical Question

The study is listed as randomized, double-masked, and parallel, with 51 participants enrolled. The posted primary endpoint compares the two groups' mean pain scores at 24 weeks. It is important to distinguish this between-group endpoint from the stated hypothesis about improvement: the record does not post baseline-to-follow-up changes or an analysis of change. The displayed group means and their unadjusted contrast therefore describe the recorded 24-week scores, not necessarily the amount of change experienced by either group.

3. Trial Design

The registry describes a randomized, double-masked, parallel-group, sham-controlled trial of custom foot orthotics in veterans with chronic lower back pain. The listed sponsor is Canandaigua VA Medical Center. The record lists a start of 2013-05, primary completion of 2016-01, enrollment of 51, and a status of terminated. The reason for termination is not reported in the registry record.

Participants were assigned to either a custom foot orthotic or a sham orthotic. The sham was described as the same as the actual orthotic without the custom support pads. The record labels the study double-masked, but does not describe the randomization sequence, allocation concealment, masking procedures, or which groups of people were masked. The planned allocation ratio and any departures from it are not reported in the registry record. The posted arm counts are 21 for the custom orthotic and 30 for the sham orthotic.

The primary outcome is the mean VAS score at 24 weeks. The record also lists the Modified Oswestry Disability Index (mODI) and PROMIS Physical Function at 24 weeks as secondary outcomes. Although the registry lists three outcome measures, it posts results for the primary outcome and these two secondary measures. It records no reported analyses. The protocol's original statistical analysis plan, its planned sample-size rationale, and any interim analysis procedures are not reported in the registry record.

Enrollment and posted arm counts describe the record, but do not establish how many participants contributed data to every outcome or whether all randomized participants were analyzed. Participant flow, follow-up completion, analysis-population definitions, and reasons for missing outcome data are not reported in the registry record. These omissions limit assessment of how closely the posted results represent the randomized groups as originally formed.

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 Visual Analog Scale (VAS), measured over 24 weeks..

The primary endpoint is the Visual Analog Scale (VAS), reported as a mean in units on a scale at 24 weeks. The registry describes the VAS as running from 0 to 100mm, where 0 is no pain at all and 100mm is the worst pain imaginable. It also states that the test has shown test-retest reliability, intra-examiner reliability, and inter-examiner reliability. These measurement properties concern consistency of measurement; they do not by themselves establish that a particular score difference is important to participants.

A continuous score retains gradations across the scale, and reporting a mean provides a group-level summary. The accompanying standard deviation describes the spread of individual scores around each group mean. Comparing the group means addresses whether the average recorded VAS score differed between assignments at the specified follow-up. It does not show the full distribution of scores, how many individuals improved, or whether any difference was meaningful to participants.

The posted primary outcome is a score at 24 weeks, not a posted change from baseline. The registry hypothesis refers to greater improvements in pain and disability, but baseline VAS results and an analysis of change are not reported in the registry record. Thus the available primary comparison should be read as a contrast of the reported follow-up means, rather than as a direct estimate of improvement over time.

7. Results Posted in the Registry

• Custom Foot Orthotic: mean 57.70 versus 59.20 on control; difference -1.50 (95% CI -10.04 to 7.04), standardized effect d = -0.10; z-test p = 0.731.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Modified Oswestry Disability Index (mODI)

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Custom Foot Orthotic: mean 40.30 versus 37.10 on control; difference 3.20 (95% CI -3.94 to 10.34), standardized effect d = 0.25; z-test p = 0.379.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Custom Foot Orthotic and the control. The interval gives the range of effects that remain compatible with the data.

Patient Reported Outcome Measurement Information System (PROMIS) Physical Function

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Custom Foot Orthotic: mean 38.30 versus 40.90 on control; difference -2.60 (95% CI -4.82 to -0.38), standardized effect d = -0.65; z-test p = 0.022.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for Custom Foot Orthotic than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The secondary measures provide additional perspectives on disability and physical function, but their numerical directions do not all align with one another or with the primary pain contrast. The registry record posts an unadjusted comparison for each measure, but does not report a pre-specified interpretation of how these outcomes should combine into an overall conclusion. These outcomes also use distinct scales, and the record does not explain thresholds for changes that participants might consider important.

The secondary findings should be read alongside, rather than as replacements for, the primary result. The primary VAS comparison does not show a clearly separated mean contrast in its unadjusted analysis. A secondary result that appears more distinct cannot independently settle the primary question, particularly when multiple outcomes have been examined and the registry record does not report a multiplicity adjustment.

Unadjusted secondary p-values do not account for the chance of finding at least one apparently notable result when several outcomes are tested. This does not make a secondary measure irrelevant, but it lowers the evidential weight that should be placed on an isolated result. The registry record lists two secondary outcomes and does not report a hierarchy, family-wise error approach, or other multiplicity plan. The secondary results are therefore most useful as exploratory context unless supported by a reported analysis plan and further evidence.

There is also no reported participant-level analysis linking changes across pain, disability, and physical function. Group means cannot show whether the same participants had concordant changes across measures. Baseline values, outcome-specific analysis populations, and missing-data procedures are not reported in the registry record, which further limits cross-outcome interpretation. These measurements broaden the description of the study, but they do not remove uncertainty about the primary comparison.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Modified Oswestry Disability Index (mODI)
• Patient Reported Outcome Measurement Information System (PROMIS) Physical Function

9. Statistical Interpretation

10. Statistical Methods Explained

The results concern continuous outcomes, each summarized by a mean and standard deviation in the two randomized groups. A mean describes the average score, while a standard deviation describes how dispersed participant scores are around that average. These summaries are useful for comparing groups, but they do not show the shape of the score distribution or whether a small number of unusually high or low observations affected the mean.

What does a mean difference represent?

For each posted comparison, the mean difference is calculated as the custom foot orthotic group mean minus the sham orthotic group mean. A value below zero means the custom group's numerical mean is lower; a value above zero means it is higher. Whether a lower score is preferable depends on the scale's scoring interpretation. The VAS description explicitly identifies the scale endpoints, but the registry record does not explain the score directions or meaningful thresholds for the secondary scales.

The posted mean differences and intervals are unadjusted recalculations from the arm-level summary statistics. An unadjusted comparison uses the posted group summaries without an adjustment for baseline scores or other participant characteristics. The registry record lists no reported analyses, so the recalculated contrasts should be distinguished from any analysis that may have been specified in a protocol or conducted by the sponsor. Such an original analysis is not reported in the registry record.

How should the interval be read?

A confidence interval expresses uncertainty around an estimated effect. In general, it gives a range of effect values that are reasonably compatible with the observed data under the method used. A narrower interval indicates greater precision than a wider interval, all else equal. If an interval crosses zero for a difference between means, it includes the possibility of no average difference as well as values in either direction. The registry record does not identify the confidence level or the exact interval-construction method, so those details should not be assumed.

What does a p-value say?

A p-value measures how surprising data at least as inconsistent with a specified null hypothesis would be, assuming that hypothesis and the statistical model are correct. It is not the probability that the null hypothesis is true, and it does not measure the size or importance of an effect. An unadjusted p-value evaluates a single contrast without accounting for the number of outcomes or comparisons considered. The registry record does not report a multiplicity strategy.

Interpretation should therefore consider the estimate and interval alongside the p-value, rather than treating a threshold as a complete summary. A p-value alone cannot establish that a difference matters to participants. Clinical importance would require context about meaningful score changes, and that information is not reported in the registry record.

Why does spread matter?

Standard deviations describe participant-to-participant variation, while the uncertainty of a group mean also depends on the number of observations contributing to it. More variation or fewer observations generally makes a mean less precise. The posted arm counts differ, and the registry record does not report outcome-specific analysis counts or missing-data handling. This makes it important not to assume that the enrollment total is the number analyzed for every outcome.

Over-dispersion is a general concern when data vary more than a statistical model assumes. If a model underestimates variability, its uncertainty estimates may be too narrow and tests may appear more decisive than warranted. The outcomes are continuous and are summarized with standard deviations; the registry record does not describe a model-based variance assessment or a check for over-dispersion. This general issue is one reason model assumptions and diagnostics matter, but no such diagnostics can be inferred from the posted summaries.

What can standardized effects add?

A standardized effect expresses a mean difference relative to a measure of outcome variability, making its scale less dependent on the original units. The recalculated comparisons include standardized effect estimates. Such estimates can help describe magnitude across measures, but their interpretation depends on the selected standardization and does not replace the raw-scale estimate. A standardized value is not itself a clinical threshold, and the registry record does not define a meaningful standardized effect for these outcomes.

The numerical comparisons are based on arm-level summaries rather than participant-level data. They cannot adjust for baseline values, explore subgroup patterns, examine individual response trajectories, or reproduce an analysis plan that is not described in the registry record. These methods explain the posted summaries; they do not fill in the unreported design or analysis decisions.

11. Confidence Intervals and Precision

The primary mean difference is -1.5 VAS units, with a reported interval from -10.04 to 7.041. The interval spans zero and extends in both directions, so the posted results do not pin down a single direction of difference between the group means. It includes values that would correspond to a lower mean in the custom group and values that would correspond to a higher mean. The p-value of 0.731 is consistent with the absence of a clearly separated group contrast in these unadjusted summaries.

Precision is not the same as whether a result is important. An interval describes uncertainty in the estimated average contrast, not the range in which most individual participants' scores fall. The standard deviations in the arms describe participant-level spread; they are not confidence intervals for the mean difference. The registry record does not state the interval's confidence level or construction method, so the quoted endpoints should be read as the reported interval without assuming additional properties.

The posted arm counts are 21 and 30, with 51 participants enrolled overall. The record does not give outcome-specific analysis counts or a participant-flow account, so it is unclear whether all enrolled participants contributed to each endpoint. The observed group means and their interval consequently need to be interpreted with the reporting limitations in mind.

Precision also depends on the outcome scale and variability. The primary result's interval is relatively broad in relation to the point estimate, leaving material uncertainty about the size and direction of the contrast. A small point estimate by itself does not show that all plausible effects are small; the interval is necessary to understand the range of estimates compatible with the analysis. Nor does an interval crossing zero prove equivalence. The registry record does not report an equivalence margin or a non-inferiority framework.

12. 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 for the continuous outcomes, not total events. The planning assumptions listed are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each planning row considers detecting the stated fraction of the observed effect. The figures are planning illustrations computed from the observed effect, not the trial's own original design assumptions; those original assumptions are not reported in the registry record.

The 80% power column describes the planned number of participants per arm that, under the listed assumptions and effect size, would give an 80% chance of rejecting the null hypothesis if that effect were the true effect. The 90% power column uses a higher target chance of detecting the assumed effect. These are prospective planning quantities, not a description of the probability that this completed trial found a real effect. This is not observed power.

Rows that plan for a smaller fraction of the observed effect require more participants per arm. That pattern follows a general principle: smaller differences are harder to distinguish from random variation, so greater sample sizes are needed to achieve the same power under otherwise similar assumptions. The calculated figures should not be mistaken for the original trial enrollment target or for evidence that the original design was adequately or inadequately powered. The registry record does not report the trial's own sample-size justification, target effect, or planned power.

Because the planning illustration uses the observed effect, its results depend on the effect estimate from a small posted study and on the assumptions used in the calculation. It does not account for unreported design features, attrition, outcome-specific missingness, multiplicity, or a clinical threshold unless those are explicitly part of the stated assumptions. The numbers are best read as conditional planning examples, not a retrospective verdict on the trial.

13. 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 = -1.500; pooled standard deviation σ = 15.190.
2. n = 2 × (1.96 + 0.842)² × 15.190² / -1.500² = 1,609.7, rounded up to 1,610 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 <- -1.5                      # observed difference in means
sigma <- 15.1896111113578                     # 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(1865539)
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 = 1,610 (80% power), 2,155 (90% power)
 75% of observed effect: n per arm = 2,862 (80% power), 3,832 (90% power)
 50% of observed effect: n per arm = 6,439 (80% power), 8,620 (90% power)
power.t.test: 1610.7 
Simulated power at n = 1,610 per arm: 0.801 (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.

14. Multiplicity, Missing Data and Analysis Populations

The registry record lists a primary outcome and two secondary outcomes, but does not report how the analyses were prioritized or how the chance of false-positive findings across multiple outcomes was handled. Multiplicity arises when several hypotheses are evaluated: even if each test is considered separately, the overall chance of at least one apparently notable result can increase. An adjustment or a pre-specified outcome hierarchy can address this concern, but neither is reported in the registry record.

The secondary comparisons are described as unadjusted recalculations from posted summary statistics. Their p-values should not be interpreted as if each were the only outcome tested. The registry record lists no reported analyses and does not identify a statistical analysis plan, so it is not possible to determine whether the posted outcomes, time point, or comparisons were selected before results were known.

Missing-data handling is also not reported in the registry record. The posted arm counts are 21 and 30, and enrollment is listed as 51, but the record does not provide participant flow, outcome-specific denominators, follow-up completion, reasons for missingness, or methods used to handle missing scores. Without these details, the summaries cannot establish whether missingness could have affected the group comparisons.

The analysis population is not defined. The registry record does not state whether analyses followed an intention-to-treat principle, included only participants with observed outcomes, or used another population. It also does not report protocol deviations, adherence, or the handling of participants who discontinued. These details matter because a comparison based on a subset can differ from the effect of assignment in the original randomized groups.

These reporting gaps do not establish that the analyses were improperly conducted. They mean that readers cannot verify multiplicity control, missing-data assumptions, or the population analyzed from the registry record alone. The posted arm summaries and unadjusted contrasts should be interpreted with that uncertainty in view.

15. 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 reports zero serious adverse events among 21 participants at risk in the custom foot orthotic group and zero among 30 at risk in the sham orthotic group. It also reports zero other adverse events in each group and zero deaths in each group. These are counts recorded in the registry, not estimates that prove the risk was absent.

Zero recorded events does not establish that the interventions have identical safety, or that no unrecorded or unreported events occurred. The registry record does not describe adverse-event definitions, ascertainment procedures, severity grading, follow-up completeness, or the time period over which the counts were collected. It also does not provide additional event terms. Interpretation is therefore limited to the posted counts and their denominators; the counts alone cannot support a broader safety conclusion.

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

The registry results describe mean scores at 24 weeks for participants assigned to custom foot orthotics or a sham orthotic. For the primary VAS outcome, the unadjusted difference between the posted means is -1.5 units, and the reported interval includes zero. The results do not establish a clearly separated difference in average follow-up pain scores. They also do not demonstrate that the groups were equivalent: the registry record does not report an equivalence margin or a design intended to establish equivalence.

The result is not a direct estimate of improvement from baseline. The stated study hypothesis refers to greater improvements in pain and disability, but baseline scores and change-from-baseline results are not reported in the registry record. A comparison at a single follow-up time can describe the groups' recorded scores at that time; without baseline results or an adjusted analysis, it cannot by itself show how much either group changed.

The secondary measures add descriptive information, but their unadjusted results do not resolve the primary uncertainty. Multiple outcomes were listed, no multiplicity strategy is reported, and the registry record does not establish the clinical meaning of the score differences. A p-value or standardized effect cannot substitute for a threshold that connects a numerical difference to a meaningful participant experience.

The posted results also do not show individual responses, durability beyond the specified follow-up, adherence, or which types of participants might have different outcomes. The record does not report participant flow or missing-data methods. Nor does it report why the trial was terminated. Those gaps constrain interpretation but should not be converted into assumptions about what happened.

Accordingly, these data are best understood as limited registry evidence about group-average scores and recorded adverse events. They do not, on their own, establish whether custom orthotics work or do not work. Broader conclusions would require appropriately reported analyses, outcome context, and study details that are not reported in the registry record.

17. Why This Trial Matters Statistically

This trial is statistically informative because it illustrates the difference between a point estimate and the uncertainty surrounding it. A mean difference can be close to zero while its interval still includes values in both directions. Reporting the estimate together with its interval prevents a single number or a p-value from carrying more certainty than the data support.

The record also highlights why endpoint definition matters. The stated hypothesis concerns improvement, but the posted primary endpoint is a mean VAS score at 24 weeks. Without baseline values or a reported change analysis, the follow-up contrast and the change question are not interchangeable. Clear reporting of the estimand—the precise contrast a study aims to estimate—helps readers assess whether the analysis answers the research question.

Randomization and masking are important design features, but labels alone do not allow readers to assess implementation. The registry identifies a randomized, double-masked, parallel design and a sham comparator, while leaving methods of sequence generation, concealment, and masking unreported. Statistical interpretation depends both on the design and on how those methods were carried out.

Finally, multiple outcomes, missing-data procedures, analysis populations, and study termination all affect the context in which estimates should be interpreted. The absence of those details does not invalidate the posted numbers; it limits the strength of conclusions that can be drawn. This record is a useful example of why transparent reporting of estimates, uncertainty, and analysis decisions is essential in clinical research.

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.

Several limitations are specific to the available record. The trial status is terminated, but the reason for termination is not reported in the registry record. The record lists an enrollment of 51 and arm counts of 21 and 30, but does not provide participant flow or explain whether the posted outcome summaries include every randomized participant. It also does not report outcome-specific denominators or follow-up completion.

The primary outcome is posted at 24 weeks, while baseline VAS scores and changes from baseline are not reported in the registry record. This limits direct interpretation of the study's stated improvement hypothesis. The record also does not provide details about randomization implementation, masking procedures, adherence, orthotic use, or protocol deviations. The sham description is limited to the absence of custom support pads.

The posted analyses are unadjusted recalculations from arm summaries, and the registry lists no reported analyses. The original statistical plan, sample-size justification, analysis population, missing-data handling, and multiplicity strategy are not reported in the registry record. These omissions prevent assessment of whether the posted contrasts match the planned primary analysis or how sensitive they might be to missing outcomes and multiple testing.

Finally, the registry does not give participant characteristics beyond the description of veterans with chronic lower back pain, nor does it provide a threshold for meaningful score changes. The reported adverse-event counts lack detail about ascertainment and collection. These limitations concern what can be learned from the registry record and should not be treated as evidence that any unreported procedure or event did or did not occur.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Efficacy of Foot Orthotics in Veterans With Chronic Lower Back Pain — NCT01865539.
• Registry record last updated 2022-05-16; status last verified 2022-04.
• Results first posted 2022-05-16.
• 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

The registry describes a randomized, double-masked, parallel sham-controlled trial of custom foot orthotics in veterans with chronic lower back pain. It lists 51 participants enrolled, a start of 2013-05, primary completion of 2016-01, and terminated status. The reason for termination is not reported in the registry record.

The primary outcome is mean VAS score at 24 weeks, with mODI and PROMIS Physical Function listed as secondary outcomes. Posted arm summaries include 21 participants for the custom orthotic group and 30 for the sham group. The unadjusted primary mean difference is -1.5 units, with a reported interval from -10.04 to 7.041 and p = 0.731. The registry lists no reported analyses. Interpretation is limited by unreported baseline results, participant flow, missing-data methods, multiplicity handling, and the original statistical plan.