Ankle Foot Orthosis Comparative Effect: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Ankle Foot Orthosis Comparative Effect (NCT03901053), a randomized na study. The primary outcome is PROMIS Patient Reported Outcomes for Physical Function.

2. Clinical Question

3. Trial Design

The registry record describes a randomized, unmasked, crossover study of two devices: Reaktiv AFO and PhatBrace AFO. Its sequence descriptions assign Reaktiv followed by PhatBrace in one arm, and PhatBrace followed by Reaktiv in the other. In a crossover design, participants may serve as their own comparison across treatment periods. That feature can be useful because measurements from the same person are often related, but the interpretation depends on how the periods, order, and within-person measurements are handled.

The record lists enrollment as 54, a start date of 2020-02-27, a primary completion date of 2023-12-18, and status as completed. It names Jason Wilken as sponsor and gives phase as NA. The endpoint summaries report group means and standard deviations, with outcome-specific numbers assessed. The registry record does not report why the analyzed numbers differ from the enrollment figure, nor does it give participant flow or reasons for missing outcome measurements.

The primary outcome is PROMIS physical function at 3 months. Secondary outcomes listed include PROMIS satisfaction with participation in social activities, the Paffenbarger Physical Activity Questionnaire, and ankle joint moment. However, the posted secondary results cover only the PROMIS satisfaction measure and ankle joint moment; the Paffenbarger measure has no result summary in the registry record. The record lists 23 outcome measures and no reported analyses. It does not report the detailed protocol, period-specific schedules, washout procedures, masking of outcome assessment, or the statistical approach originally intended for the crossover data.

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: Four (4) of the participants in this study failed the post-informed consent screening checklist, and were excluded form the study before being assigned to either group. The fifty (50) eligible participants were randomized to one of the two groups.

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.

Population: All participants completed study activities in each of the experimental conditions in a randomized order (Reaktiv, PhatBrace; PhatBrace Reaktiv)

6. Primary Endpoint

The registry lists the primary outcome as PROMIS Patient Reported Outcomes for Physical Function, measured over 3 months.

The primary endpoint is PROMIS Patient Reported Outcomes for Physical Function, measured with a computerized adaptive test and reported as a mean T-score at 3 months. PROMIS is a patient-reported outcome system: it captures a person’s report of their own functioning rather than relying only on a physical examination or device measurement. A computerized adaptive test selects questions based on earlier responses, with the aim of measuring the relevant domain efficiently.

The registry description explains the T-score reference: 50 is the mean of a relevant reference population, and 10 is that population’s standard deviation. A score above 50 represents more of the measured variable than the reference-population average. The registry record does not give a threshold for a clinically important difference in this study, so a numerical contrast should not be treated as clinically meaningful simply because it is above or below zero.

Physical function is relevant to a comparison of ankle-foot orthoses because it captures participants’ reported ability to function. The posted endpoint summarizes the group means and standard deviations and gives an unadjusted comparison. Because the design is crossover, an analysis that uses within-person information could be important; the registry record does not report such an analysis or explain how the 3-month measurement relates to each device period.

7. Results Posted in the Registry

• PhatBrace: mean 45.02 versus 44.78 on control; difference 0.24 (95% CI -3.71 to 4.19), standardized effect d = 0.03; z-test p = 0.905.

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.

PROMIS Patient Reported Outcomes for Satisfaction With Participation in Social Activities

• 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:
  • PhatBrace: mean 48.42 versus 49.39 on control; difference -0.97 (95% CI -4.99 to 3.05), standardized effect d = -0.13; z-test p = 0.637.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between PhatBrace and the control. The interval gives the range of effects that remain compatible with the data.

Ankle Joint Moment

• 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:
  • PhatBrace: mean 1.29 versus 1.43 on control; difference -0.14 (95% CI -0.26 to -0.02), standardized effect d = -0.62; z-test p = 0.027.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for PhatBrace than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The secondary outcomes do not form a uniformly aligned pattern with the primary result. The social-activities PROMIS measure is another patient-reported outcome, while ankle joint moment is a biomechanical measure. The posted comparisons differ in their direction and uncertainty, and the ankle joint moment comparison is the one whose reported interval excludes zero. The Paffenbarger Physical Activity Questionnaire is listed as a secondary outcome, but a result summary for it is not reported in the registry record.

These measures address related but distinct aspects of function and activity. A finding in a biomechanical measure does not necessarily predict a change in how participants report physical function, and a patient-reported measure need not move in parallel with a mechanical measure. The primary endpoint remains the main outcome for the stated trial question. Secondary results can add context, but they do not replace the primary comparison or resolve its uncertainty.

The secondary comparisons are unadjusted. When several outcomes are examined, the chance of seeing at least one apparently notable result by chance can increase. General approaches to multiplicity include specifying a priority order in advance, adjusting the testing threshold, or treating secondary analyses as exploratory. The registry record does not report which approach, if any, was intended or used. No multiplicity-adjusted analyses are listed.

For that reason, an isolated secondary result should carry less weight than a consistent pattern supported by a prespecified analysis and a clear account of uncertainty. The absence of a reported result for one listed secondary measure also limits the overall picture. The record does not explain whether that outcome was not collected, not analyzed, or simply not posted, so no reason should be inferred.

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

• PROMIS Patient Reported Outcomes for Satisfaction With Participation in Social Activities
• Paffenbarger Physical Activity Questionnaire
• Ankle Joint Moment

9. Statistical Interpretation

10. Statistical Methods Explained

The posted continuous outcomes are summarized with a mean and standard deviation for each device, followed by an unadjusted mean difference, an interval estimate, and an unadjusted p-value. These are straightforward descriptions of the posted summaries. The registry record does not report sponsor analyses, a detailed statistical analysis plan, or an explanation of whether the posted comparisons reflect the intended crossover analysis.

What does a mean difference represent?

A mean is the arithmetic average of a set of scores. A mean difference expresses the contrast between two group means in the outcome’s original units. For the primary measure, the posted means are 44.78 for Reaktiv and 45.02 for PhatBrace, and the reported mean difference is 0.24. This is a small point estimate on the score scale, but its interpretation depends on uncertainty and on whether the method appropriately reflects the study design. A mean difference is not itself a statement about individual participants: people’s scores can vary around each group mean.

Why report a standard deviation?

The standard deviation describes how spread out observed scores are around their mean. The primary summaries report standard deviations of 6.01 for Reaktiv and 8.35 for PhatBrace. Greater spread means that observations are less tightly clustered around the mean. The standard deviation is not the same as the standard error: the standard deviation describes variation among observations, while a standard error describes uncertainty in an estimated quantity. Neither measure alone tells whether a difference is clinically important.

What does an interval estimate add?

An interval estimate gives a range of values compatible with the observed data under the method used. It makes uncertainty visible instead of presenting only a single point estimate. For the primary mean difference, the reported interval runs from -3.715 to 4.195. Since it crosses zero, the posted comparison does not rule out a difference in either direction. The confidence level and exact calculation method for these intervals are not reported in the registry record, so the interval should be interpreted as posted rather than attributed to a particular unreported procedure.

How should the p-value be read?

A p-value measures how unusual the data, or results more extreme, would be under a specified null model and its assumptions. It is not the probability that the null hypothesis is true, nor does it measure the size or importance of an effect. The primary unadjusted p-value is 0.905. It is consistent with the lack of a clear separation in the posted summaries, but it does not prove that the devices have identical effects. The record does not report a sponsor analysis or a specified inferential model, and the unadjusted value should not be mistaken for an analysis that accounts for all features of the crossover design.

Why does the crossover design matter?

In general, crossover data can contain paired observations: the same participant may contribute measurements under both devices. Paired observations tend to be related, and a method that accounts for this relationship can use information about within-person changes. Treating device summaries as if they came from unrelated groups can fail to represent that relationship and can give a different estimate of uncertainty. Order and period can also matter: outcomes may differ depending on which device is used first or when a measurement is taken. A carryover effect is a lingering influence from an earlier treatment period that affects a later period. These are general design considerations, not claims that any such effects occurred in this trial.

The record gives sequences and identifies the study as crossover, but does not report period-specific summaries, a paired comparison, the within-person covariance, sequence-adjusted estimates, or any approach to possible carryover. The posted unadjusted summaries can therefore be described, but their relationship to a full crossover analysis remains unclear.

What is an unadjusted recalculation?

An unadjusted recalculation derives a simple comparison from the posted summary statistics without adjusting for additional variables or design features. It can help readers understand the direction and rough scale of the displayed data, but it is not equivalent to the sponsor’s planned analysis. In this record, no sponsor-reported analyses are listed and the discrepancy indicator is false. There is therefore no reported sponsor estimate to contrast with the recalculated summary, while the absence of an analysis report remains an important limitation.

General statistical interpretation also depends on assumptions such as how observations were selected, whether missing outcomes are related to the results, and whether the analysis matches the allocation and measurement structure. The registry record does not report enough detail to assess those assumptions comprehensively. The posted estimates should be read as descriptive and unadjusted evidence, with uncertainty, rather than as a complete account of the randomized crossover comparison.

11. Confidence Intervals and Precision

The primary mean difference is 0.24, with a reported interval from -3.715 to 4.195. The interval is broad relative to the point estimate and spans zero. That means the posted data do not pin down the direction of the difference: values favoring either device, as well as a value near no difference, remain compatible with the interval. The registry record does not report the confidence level used for the interval.

Precision is not the same as whether a result is statistically significant. A point estimate can be close to zero while still having substantial uncertainty, as in this comparison. Conversely, an interval that excludes zero does not by itself establish a clinically important difference. The record does not give a clinically important threshold for PROMIS physical function, so clinical importance cannot be determined from the interval alone.

For the social-activities PROMIS outcome, the reported mean difference is -0.97, with an interval from -4.994 to 3.054; it also includes zero. For ankle joint moment, the estimate is -0.14, and the reported interval excludes zero. Its endpoints are not repeated because they are recorded to more than three decimal places. These secondary outcomes measure different constructs and do not narrow the uncertainty around the primary endpoint.

The interval estimates are based on the posted unadjusted comparisons. In a crossover trial, precision can depend on how strongly within-person measurements are related and on the analysis of sequence and period. Those details are not reported in the registry record. The intervals therefore communicate uncertainty for the posted comparisons, but the record does not establish that they fully reflect the crossover design.

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, not total events. They are illustrations based on the observed effect, not the trial’s original design calculation. The listed 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 at the stated fraction of the observed effect. The original trial’s sample-size assumptions and justification are not reported in the registry record.

The 80% power column describes the planned number of participants per arm under those assumptions for a design that would have an 80% chance of detecting the specified effect if that effect were present. The 90% power column describes the corresponding planning target for a design with a 90% chance. These are design probabilities under an assumed effect and model; they do not tell whether the completed study detected an effect. This is not observed power.

The entries are conditional on the assumed effect size. Planning for 75% of the observed effect requires more participants per arm than planning for the full observed effect, and planning for 50% requires more again. In general, smaller effects are harder to distinguish from random variation and require more participants under otherwise comparable assumptions. The effect used in these illustrations is the observed point estimate, which is itself uncertain; a planning illustration based on that estimate should not be treated as a reliable forecast of the effect in a future study.

The registry record identifies a crossover design, while these listed planning assumptions describe equal allocation between two arms and a normal approximation. It does not report a crossover-specific sample-size method or account in the planning figures for within-person correlation, sequence, or period effects. The figures are therefore best read as simple planning illustrations, not as evidence that the trial was designed or powered according to those assumptions.

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 = 0.240; pooled standard deviation σ = 7.275.
2. n = 2 × (1.96 + 0.842)² × 7.275² / 0.240² = 14,422.7, rounded up to 14,423 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 <- 0.240000000000002                      # observed difference in means
sigma <- 7.27470274306793                     # 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(3901053)
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 = 14,423 (80% power), 19,308 (90% power)
 75% of observed effect: n per arm = 25,641 (80% power), 34,326 (90% power)
 50% of observed effect: n per arm = 57,691 (80% power), 77,232 (90% power)
power.t.test: 14423.6 
Simulated power at n = 14,423 per arm: 0.799 (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 23 outcome measures and reports no analyses. It does not identify a statistical analysis plan, a prespecified hierarchy among outcomes, or a multiplicity procedure. When several outcomes or comparisons are examined, some may appear notable by chance even if there is no underlying difference. General strategies include controlling the family-wise chance of false-positive findings, controlling the expected proportion of false discoveries, or clearly labeling secondary analyses as exploratory. Which strategy applies to this study is not reported in the registry record.

The primary comparison has an unadjusted p-value, and the secondary comparisons are also unadjusted. Their p-values should therefore be interpreted as individual comparisons rather than as results adjusted for the full set of outcomes. The ankle joint moment result should not be treated as confirmatory solely because its reported interval excludes zero. The record does not say whether that outcome was designated as confirmatory, whether its analysis was planned in advance, or how it fits into any testing hierarchy.

Missing-data handling is also not reported in the registry record. The outcome summaries include their own assessed numbers, but there is no participant-flow account, no explanation for missing measurements, and no description of imputation or other missing-data methods. In general, missing outcomes can affect estimates if the probability of being measured is related to a participant’s outcome or treatment experience. Without information about why measurements are absent and how they were handled, the direction or size of any resulting bias cannot be assessed.

The analysis population is not specified. The record does not say whether analyses followed randomized sequence assignment, included only participants with measurements under both devices, or used another population definition. It also does not report how protocol deviations or incomplete crossover periods were handled. These details matter for understanding which participants contribute to an estimate and whether the analysis preserves the randomized comparison.

Finally, the registry record does not report the original analysis plan, interim analyses, or any adjustments for sequence, period, or carryover. These omissions do not prove that such procedures were absent; they mean that their use cannot be established from the record. The posted summaries are consequently best interpreted with the stated limits on multiplicity, missingness, and analysis-population information.

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 adverse-event record lists Reaktiv and PhatBrace separately. For each device, the serious adverse-event group has 50 participants at risk and 0 affected; the other adverse-event group also has 50 at risk and 0 affected. Deaths are recorded as 0 for each. No serious adverse-event terms are listed.

These figures describe what is posted in the registry record, not a comparison adjusted for exposure time or participant overlap. Because the study is crossover, a participant may contribute experience under both devices; the record does not explain whether the at-risk figures represent unique people, device-period exposure, or another reporting convention. The safety summaries should not be added across devices to infer a number of distinct participants.

Zero reported events means no events are recorded in these categories in the posted figures. It does not establish that no event occurred outside the reported definitions, observation periods, or reporting process. The registry record does not provide event-specific follow-up duration, severity detail beyond the listed categories, or an explanation of how adverse events were collected. These limits prevent a broader safety conclusion from being drawn from the figures alone.

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

The posted primary comparison shows similar group means, with a small mean difference of 0.24 and a wide interval that includes zero. The unadjusted p-value is 0.905. This is evidence that the posted summaries do not clearly distinguish the mean PROMIS physical-function scores, but it is not proof that the devices have identical effects. The interval leaves uncertainty in both directions, and the registry record does not report a clinically important difference threshold for the score.

The comparison also needs to be understood in light of its crossover design. The registry record gives the device sequences but does not report a paired, sequence-adjusted, or period-adjusted analysis. Without such information, it is not possible to determine whether the posted summaries fully use the within-person structure or account for possible order and period effects. The figures describe the record, not a definitive estimate under every feature of the design.

The secondary outcomes offer additional but limited context. They include a patient-reported social-activities measure and ankle joint moment, while a result for the listed physical-activity questionnaire is not reported. Their different constructs and unadjusted analyses mean they should not be combined into a single conclusion about function. The secondary findings do not overturn the uncertainty in the primary endpoint.

These results do not establish that either device works or does not work, and they do not determine which device a person should use. They are not medical advice. They describe a randomized comparison as recorded, with limited analysis and missing-data detail. A fuller interpretation would require the original analysis plan, participant flow, crossover-specific estimates, and a clear account of missing outcomes and multiplicity, none of which is reported in the registry record.

17. Why This Trial Matters Statistically

This trial is statistically interesting because its crossover design could allow a comparison within participants, while the posted outcomes are presented as device-specific means and standard deviations. That contrast highlights a central issue in clinical-trial interpretation: the analysis should reflect how participants were assigned and how measurements were collected. In a crossover study, paired information, treatment order, and period may all matter. The registry record does not report how these features entered the analysis.

The primary estimate also illustrates why a point estimate and its uncertainty should be read together. The estimated mean difference is close to zero, but the interval is wide enough to include differences in either direction. A p-value alone cannot convey that range, establish equivalence, or describe clinical importance. The registry record does not provide an equivalence margin or a threshold for a meaningful PROMIS score difference.

Secondary outcomes raise another general lesson: a result from one measure should be considered alongside the number and types of outcomes examined. Here, the record lists numerous outcome measures, but does not report a multiplicity strategy or a complete set of analyses. An unadjusted secondary finding can be informative as context, but its evidential weight depends on whether it was prespecified and how it relates to other outcomes. Those details are not reported in the registry record.

Finally, planning illustrations based on an observed effect are not the same as the original design justification. The record does not report the trial’s original sample-size assumptions, and the posted planning figures use a simple normal approximation rather than a reported crossover-specific calculation. This distinction helps prevent a planning scenario from being misread as evidence about the study’s observed ability to detect an effect.

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 main limitation for interpreting the primary comparison is the absence of a reported analysis tailored to the crossover design. The registry record identifies randomized sequences but does not provide paired estimates, within-person correlations, period-specific results, or methods for handling sequence and possible carryover. Consequently, the posted unadjusted comparison may not capture all information or design features relevant to the treatment contrast.

The record also gives limited information about participants and outcome completeness. It records enrollment as 54, but does not provide a flow diagram, eligibility details, demographic or clinical characteristics, or explanations for missing measurements. The outcome summaries report their own assessed numbers, but the reasons for differences between those numbers and enrollment are not reported in the registry record. Analysis-population definitions and missing-data methods are also not reported.

Multiplicity is another limitation. The record lists 23 outcome measures, while no reported analyses or adjustment strategy are listed. A secondary result may be more vulnerable to chance findings when many outcomes are considered, particularly when the analysis hierarchy is unknown. The record does not state whether all listed outcomes were prespecified or explain the status of the physical-activity questionnaire result.

The interpretation of score differences is constrained by the absence of a stated clinically important threshold for PROMIS physical function. The confidence level and calculation method for the posted intervals are not reported. Safety figures are limited to the recorded event categories and at-risk counts, without further detail about exposure time or collection methods. These omissions limit what can be inferred from the registry record; they do not establish that a particular procedure or safeguard was absent from the conducted trial.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Ankle Foot Orthosis Comparative Effect — NCT03901053.
• Registry record last updated 2026-01-29; status last verified 2025-10.
• Results first posted 2025-10-31.
• 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 record describes a completed randomized, unmasked crossover study of Reaktiv and PhatBrace ankle-foot orthoses. Enrollment is recorded as 54. The primary endpoint is PROMIS physical function at 3 months, summarized by device mean and standard deviation. The posted unadjusted mean difference is 0.24, with an interval from -3.715 to 4.195 and p = 0.905.

Secondary summaries include PROMIS satisfaction with participation in social activities and ankle joint moment; a result for the listed physical-activity questionnaire is not reported. Adverse-event figures record no serious events, other events, or deaths in the listed groups. No sponsor analyses, crossover-specific inferential analysis, multiplicity method, missing-data approach, or original sample-size justification is reported in the registry record. The results therefore describe posted summaries with substantial limits on interpretation.