Variability and Specificity in Reactive Stabilization Movements to Diverse Slip Perturbations: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Variability and Specificity in Reactive Stabilization Movements to Diverse Slip Perturbations (NCT03755336), a na na study. The primary outcome is Fall Rates.

2. Clinical Question

3. Trial Design

The registry describes a completed, single-group study sponsored by the University of Nebraska. Its enrollment is 44. The study began on 2019-12-01, and primary completion is listed as 2024-01-01. The record identifies the study as non-randomized and does not describe masking. The study is not presented as a comparison of an intervention group with a control group.

Participants were drawn from two age groups: younger adults aged 19 - 35 years and older adults aged 65-79 years. Each participant was scheduled for three visits within the span of 1 week. At the initial visit, participants completed informed consent, demographic and body-measurement collection, and medical and physical-activity questionnaires. Upper- and lower-body strength was measured at the first and last visits.

Each visit included a gait variability assessment followed by slip perturbations during overground walking. The perturbations occurred at early, middle, and late stance. The study summary describes four slips in each phase on each visit, while the arm description characterizes exposure as a series of 12 unannounced perturbations. Planned measures included falls, slip severity, and reactive stabilization movements.

The primary endpoint is fall rates. Other named outcomes concern heel displacement and sliding velocity, trunk angular momentum, recovery-step position and timing, and stride-time variability and entropy. The registry lists eight outcome measures. It does not report a detailed statistical analysis plan, a sample-size justification, or an explanation of how repeated observations within participants were handled. Those design and analysis details are not reported 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.

Overall Study

Analysis population for the primary outcome, as defined in the registry: Participants were administered slips 12 times in a session for each of 3 sessions.

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 Fall Rates, measured over Up to 7 days.

The primary endpoint is the percentage of trials resulting in a fall. The registry defines a fall using force measured by a load cell in the harness system: a trial is classified as a fall when the maximum force exceeds 30% body weight. This operational definition makes the outcome a trial-level event classification rather than a broader clinical judgment about an individual’s general fall risk.

Fall rates are relevant to the study’s stated purpose because the project examines reactive stabilization after slips at different points in the gait cycle. A fall classification captures whether a perturbation led to a specified harness-force threshold being crossed. It does not, by itself, describe the severity or mechanics of every slip, which is why the registry also names outcomes such as heel displacement, sliding velocity, trunk angular momentum, and recovery-step measures.

The stated timeframe is up to 7 days, and the population description indicates that participants were administered slips 12 times in a session for each of three sessions. The record does not provide the observed percentage of trials resulting in falls, the underlying fall and trial counts, or an estimate of uncertainty for the primary endpoint. Those results are not reported in the registry record, so the endpoint definition can be described but its observed value cannot be interpreted.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry specifies an outcome definition and a study structure, but it does not provide enough analysis detail to reconstruct a statistical method for the primary endpoint. The following concepts are general explanations of issues that matter when analyzing this kind of repeated-trial study; they are not claims about methods used by the investigators.

What does a trial-level fall rate represent?

A fall rate is a proportion: the number of trials meeting the stated fall definition in relation to the number of trials evaluated. The registry’s definition uses the maximum force on a harness-system load cell, with a fall classified when that force exceeds 30% body weight. The resulting measure depends on the classification rule and on which trials are included in the denominator. Reporting only a percentage, without the underlying counts or a clear denominator, can make it difficult to assess the amount of information behind the estimate. The registry record does not provide the observed rate or its underlying counts.

Why does repeated exposure matter?

Each participant experienced repeated perturbations across visits and gait phases. In general, observations from one participant may be more alike than observations from different participants because they share characteristics of that individual. Treating all trials as independent can make uncertainty estimates too narrow when within-person dependence is present. Methods for repeated or clustered data can account for this dependence, but the appropriate method depends on the design and estimand. The registry record does not report whether a repeated-measures, clustered, or other model was used.

Repeated exposure can also raise questions about order and learning. For example, a statistical analysis might need to consider whether responses vary across phases, visits, or the sequence of perturbations. These are general design considerations, not findings about this study. The registry describes the visit schedule and perturbation phases but does not report an analysis of order effects, learning, or adaptation.

How should age groups be understood?

The study includes younger and older adults, but is described as a single-group study with no randomized comparison. Age-group summaries could describe the observed participants, but a difference between groups would not automatically identify an effect caused by age. Interpretation would depend on the analysis, participant characteristics, and how repeated trials were handled. The registry record does not report a primary outcome comparison by age group or an adjusted analysis.

What does uncertainty add?

In general, a confidence interval describes a range of values compatible with the data and the assumptions of the method used. Its width communicates precision: a wider interval indicates less precise estimation than a narrower one. For repeated-trial outcomes, valid uncertainty estimates depend on accounting appropriately for dependence and the study’s sampling structure. No confidence interval for the fall rate is reported in the registry record, so its precision cannot be assessed.

What can a p-value establish?

In general, a p-value summarizes how incompatible the observed data are with a specified null hypothesis under the assumptions of a statistical test. It is not the probability that the null hypothesis is true, and it does not measure the size or importance of an effect. The registry record lists no analyses and reports no p-value for the primary endpoint. There is therefore no reported inferential test to interpret.

How do planning illustrations differ from study results?

Sample-size planning illustrations are hypothetical calculations under stated assumptions. The record describes an illustration using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. Such assumptions do not establish that the trial was designed or analyzed that way. Planning estimates are not observed power, and they do not substitute for an observed effect estimate with uncertainty. The record does not report the trial’s own sample-size justification or statistical plan. Because this study is described as single group, an illustrative calculation based on two arms should not be mistaken for the study’s actual design.

In general, over-dispersion occurs when observed variation is greater than a model’s assumptions allow. For count or binary outcomes, failing to account for such extra variability can lead to uncertainty estimates that are too optimistic. Whether over-dispersion is relevant depends on the particular model and data. The registry record does not identify a model or report a dispersion estimate, so no conclusion about over-dispersion in this study is possible.

10. Multiplicity, Missing Data and Analysis Populations

The registry identifies fall rates as the primary outcome and also lists other measures of slip response and gait variability. These include heel displacement, maximum heel sliding velocity, trunk angular momentum, recovery-step position and timing, coefficient of variation of stride time, and sample entropy of stride time. Considering multiple outcomes can raise a multiplicity question: when several hypotheses are tested, the chance of at least one apparently unusual result can increase. General approaches include prespecifying a primary hypothesis, adjusting inference, or treating secondary analyses as exploratory. The registry record does not report a multiplicity strategy or a hierarchy for interpreting the secondary outcomes.

The record does not provide observed outcome data, analysis populations, or the handling of missing observations. It is therefore not reported in the registry record whether all enrolled participants contributed data to each outcome, how incomplete visits or unusable trials were treated, or whether missingness was addressed with a particular method. These details matter because exclusions or missing trial data can affect both the denominator of a fall rate and the population represented by an estimate.

The registry states that participants completed repeated visits and perturbations, but does not report whether analyses used all trials, summarized results per participant, or used a model that retained trial-level data. It also does not describe whether the primary analysis was intention-to-treat, per-protocol, or based on another analysis population. No prespecified statistical analysis plan, interim analysis, or missing-data strategy is reported in the registry record. Without these details and the actual results, neither multiplicity control nor the robustness of any estimate can be evaluated.

11. 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’s adverse-event record lists younger and older adult groups, with 22 participants at risk in each group. For each group, the recorded counts are zero serious adverse events, zero other adverse events, and zero deaths. These are the counts entered in the registry record; they should not be interpreted as proof that no adverse event of any kind occurred outside the recorded categories or observation process.

Adverse-event counts are distinct from the primary endpoint. A fall is defined for the primary endpoint using the maximum harness load-cell force during a trial, whereas the safety record classifies serious and other adverse events. The registry does not report whether a trial meeting the fall definition was also recorded as an adverse event. The two kinds of information should not be assumed to correspond one-to-one.

The record does not provide further detail about adverse-event collection procedures, severity grading beyond the serious/other categories, causal attribution, or the duration of safety follow-up. The zero counts should therefore be read narrowly as the counts recorded for the listed groups, rather than as a comprehensive assessment of safety or a comparison with an untreated group. The study has no randomized control group described in the registry record.

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

The record establishes that a completed single-group study examined responses to slip perturbations delivered during early, middle, and late stance. It specifies a fall-rate endpoint and a load-cell threshold for classifying falls, and names movement and gait-variability outcomes. These are the aspects of the study that can be described from the registry entry.

The record does not report observed fall rates, results for the secondary outcomes, effect estimates, confidence intervals, or statistical tests. It therefore does not establish the frequency of falls in the study, whether responses differed across perturbation phases, or whether outcomes differed by age group. The lack of an observed result in the registry record is not evidence that an effect was absent; it means the result cannot be evaluated from this record.

The single-group design also limits what could be inferred from within-study observations. Without a randomized control group, the record cannot support a randomized treatment comparison. A change across visits, if one were reported, would require interpretation in light of repeated exposure and other possible explanations. No such result or analysis is reported in the registry record.

In general, an outcome definition is not an outcome finding. A precise threshold can make the measurement rule explicit, but interpretation still requires the observed data, denominators, analysis method, and uncertainty. Likewise, a completed study status does not provide the missing estimates. The registry record supports a description of the research question and methods as registered, but not a conclusion about the magnitude, precision, or direction of the primary result.

13. Why This Trial Matters Statistically

The study addresses a measurement issue that is important for interpreting perturbation experiments: a slip can occur at different points in the gait cycle, and the study describes a design that samples early, middle, and late stance. Focusing on the timing of perturbations can help organize the scientific question around specific movement responses rather than treating every slip as interchangeable. The registry also names several biomechanical and gait-variability measures alongside the fall classification.

Statistically, the repeated-trial structure is central. Trials are nested within participants and occur across visits and phases. General analysis of such data needs to distinguish the number of trials from the number of independent participants and to account for within-participant dependence when estimating uncertainty. The registry describes repeated exposure but does not report the analysis method, so it cannot show how that issue was handled.

The distinction between a clearly defined endpoint and a reported result also matters. The load-cell threshold makes the fall classification operational, while the absent estimate leaves the primary question unanswered in the registry record. Without counts or uncertainty estimates, readers cannot judge either the observed event frequency or the precision of the estimate.

The study therefore illustrates both the value and limits of registry information. Its design and intended outcomes are described in enough detail to identify the population, perturbation schedule, and primary measurement. However, without posted analyses and results, the statistical evidence about the primary question cannot be assessed from the registry entry.

14. 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.

A key limitation for interpretation is that the primary outcome result is not reported in the registry record. Neither the fall-rate estimate nor its underlying trial counts and uncertainty are available there. The listed outcome definition alone cannot establish what was observed.

The study is single group and has no randomized control group described in the registry. It therefore does not provide a randomized comparison with an untreated or alternative-treatment group. The two age groups are population categories, not a stated randomized contrast. The record does not report whether age-group outcome estimates were calculated or how potential differences were handled.

The design involves repeated perturbations within participants across visits and gait phases. The registry does not report whether the analysis accounted for correlation among repeated trials, how visit or perturbation order was modeled, or how incomplete visits and missing trials were handled. It also does not report analysis populations, a statistical analysis plan, or a sample-size justification.

The primary endpoint uses a specified harness-force threshold, but the registry record does not provide further information about the availability of trial-level data, outcome adjudication, or the relation between fall classifications and adverse-event reports. Safety information is limited to the listed event counts. These limitations concern what can be evaluated from the registry record and do not establish that the study itself lacked procedures or analyses not recorded there.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Variability and Specificity in Reactive Stabilization Movements to Diverse Slip Perturbations — NCT03755336.
• Registry record last updated 2025-05-25; status last verified 2025-05.
• Results first posted 2025-05-25.
• 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.

18. Record Summary

The registry identifies a completed, single-group study of reactive stabilization after slip perturbations at different points in the gait cycle. It lists enrollment of 44 and describes younger adults aged 19 - 35 years and older adults aged 65-79 years. Participants were scheduled for three visits within the span of 1 week, with gait variability assessments and repeated slip perturbations.

Fall rates are the primary outcome, defined by whether harness-system load-cell force exceeds 30% body weight. Other named outcomes cover slip movement, trunk motion, recovery steps, and stride-time characteristics. The registry lists zero analyses and does not report observed primary or secondary outcome results, statistical estimates, or a detailed analysis plan. Adverse-event counts recorded for both age groups are zero for serious events, other events, and deaths. The registry record supports description of the design and outcome definitions, but not an assessment of the observed effects or their precision.