Powered Seating Function Usage Among Veterans - Compliance and Coaching: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Powered Seating Function Usage Among Veterans - Compliance and Coaching (NCT00839098), a randomized na study. The primary outcome is Compliance Rate.

2. Clinical Question

The study asked how Veterans used powered wheelchairs and powered seating functions, and whether instruction could improve compliance with recommended pressure-relief, upper-limb-preservation, and discomfort-management practices. It also examined whether adding a virtual coach to instruction was associated with a different compliance result.

The recommendation required use of a moderate or maximum range of tilt at least once every hour for 2 minutes. Compliance required following the recommended position, duration, and frequency and completing a successful repositioning exercise. The registry also describes broader aims involving activity, participation, and seating discomfort, and lists questionnaire outcomes related to discomfort, psychological impacts of assistive devices, and independence in the community. Those broader aims do not change the specific primary comparison reported for compliance.

The available record does not establish whether all randomized participants contributed to the primary analysis, nor does it provide detailed eligibility criteria or a complete account of each participant’s exposure to the interventions. Those details are not reported in the registry record.

3. Trial Design

This was a randomized, parallel-group trial with no masking reported. The registry marks the phase as not applicable and the study status as completed. It lists 28 participants as enrolled. The study began in 2011-11, and primary completion was recorded as 2013-12.

Three groups are named: Control Group, Instruction Group, and Instruction and Virtual Coach Group. The instruction intervention consisted of verbal and written instruction on power-seat-function use. The other intervention added a virtual coach to verbal and written instruction. The control group is listed in the registry, but the primary-outcome results give no control-group mean, standard deviation, or analyzed participant count. The study’s allocation method is described as randomized; the randomization procedure, allocation concealment, and group assignment details are not reported in the registry record.

The primary measure was compliance rate, expressed as a percentage of participants’ compliance. The record describes the endpoint as the difference between baseline and week 7-8, with the measurement period occurring every 2 weeks for 8 weeks following wheelchair acquisition. It reports a mean and standard deviation for the two instruction groups: the Instruction Group had n = 10, mean 8.9, and standard deviation 15.9; the Instruction and Virtual Coach Group had n = 6, mean 39.7, and standard deviation 23.5. The control-group endpoint count is n = 0, with no reported mean or standard deviation.

The registry reports one primary-outcome comparison, using the Wilcoxon (Mann-Whitney) method, between the two instruction groups. The reported p-value is 0.27. Confidence intervals and a treatment-effect estimate for that comparison are not reported in the registry record. The reported endpoint analysis was limited to participants who completed the study protocol and used the wheelchair; further details about analysis populations and participant flow are not reported.

The registry does not report the planned sample-size justification, detailed randomization methods, protocol deviations, masking of outcome assessment, or a full statistical analysis plan. These omissions mean that the design features that can be described are limited to the randomized parallel structure, the listed groups and interventions, and the outcome information posted in the 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

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Only the data of the participants who completed the study protocol and use the wheelchair were included in the data analysis.

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: The average age of the participants was 53.2 years old (+/- 14.0 years old). Twelve out of 28 were female (42.9%). Two of the participants were veterans, and one of them was recruited from VA Wheelchair Seating clinic. Arm 1 (control group) was removed from the study through IRB modification because of difficulties in recruiting participants.

6. Primary Endpoint

The registry lists the primary outcome as Compliance Rate, measured over Every 2 weeks for 8 weeks following acquisition of wheelchair.

The primary endpoint is a change in compliance with a recommended powered-seat repositioning routine. The routine called for using a moderate or maximum range of tilt at least once every hour for 2 minutes. A repositioning exercise counted as compliant only when the participant followed the recommended position, duration, and frequency and completed the exercise successfully.

The registry defines a participant’s compliance rate as successful repositioning exercises divided by the total of successful and missed repositioning exercises. The reported result is the difference between baseline and week 7-8, with assessments described as occurring every 2 weeks for 8 weeks following wheelchair acquisition. This endpoint therefore concerns change in recorded use of the recommended routine over the stated observation period, rather than a single observation of wheelchair use.

Such a measure is used to operationalize whether participants follow a specified practice. It makes the study question more concrete than a broad aim such as improving wheelchair use: the outcome has stated requirements for position, duration, and frequency. In general, a compliance measure depends on how events are recorded and classified, so the interpretation also depends on the completeness and consistency of those records. Further details about monitoring, missing observations, and the handling of incomplete repositioning records are not reported in the registry record.

The outcome is reported as a mean change and standard deviation for the two instruction groups. No primary-endpoint result is reported for the control group, and no confidence interval for the reported comparison is posted. The reported endpoint should therefore be read as the observed summary for the analyzed participants in the two listed instruction groups, not as a complete three-group estimate.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does the reported test compare?

The registry names the Wilcoxon (Mann-Whitney) test for the comparison between the Instruction Group and the Instruction and Virtual Coach Group. In general, this rank-based method compares the ordering of observations from two independent groups. It uses the ranks of the observed values rather than relying directly on a comparison of group means. Under suitable assumptions, it can be used to assess whether the groups’ outcome distributions differ. It is not automatically a test of medians: that interpretation requires additional assumptions about the shapes of the distributions.

The reported group summaries are means and standard deviations, but the reported inferential method is rank-based. Those are different summaries of the data. Means describe averages, and standard deviations describe dispersion around the mean; the rank test evaluates the relative ordering of observations. The record does not report the rank distributions, test statistic, exact-versus-approximate calculation, or any supporting diagnostic information.

How should the p-value be read?

The reported p-value is 0.27. In general, a p-value describes the compatibility of the observed data with a null model for the test, assuming the model and test conditions are appropriate. A p-value is not an effect estimate and does not show how large a difference is. It also does not give the probability that a treatment is effective or ineffective. Interpretation is strongest when a p-value is considered alongside an estimated contrast and its uncertainty, but no confidence interval or numerical between-group estimate is reported in the registry record.

The record does not state the significance threshold used for the primary analysis, nor does it describe whether the reported p-value is adjusted for multiple testing. The planning illustration assumptions elsewhere in the record do not establish the threshold or multiplicity procedure used in the trial’s analysis. Therefore, the p-value should be quoted as reported without implying an unreported analysis rule.

What do the means and standard deviations tell readers?

The Instruction Group has a reported mean of 8.9 and standard deviation of 15.9, based on n = 10. The Instruction and Virtual Coach Group has a reported mean of 39.7 and standard deviation of 23.5, based on n = 6. These are summaries of the endpoint values in the analyzed groups. The standard deviation describes variability among participants; it is not a confidence interval and does not indicate how precisely the mean is estimated. The registry does not post confidence intervals for either mean or for the comparison.

The endpoint is a change from baseline to week 7-8, while the registry labels the summary as a mean and standard deviation. The values should be interpreted in that context. They are not the proportion of participants who complied, nor do they show each participant’s pattern over time. The record does not report the distribution of individual changes, repeated-measures model, or whether observations across the monitoring period were handled in any additional way.

Why does the missing control result matter?

A randomized design can support comparisons among assigned groups when outcomes are available and analyzed appropriately. Here, the control group is listed, but its primary endpoint is recorded as n = 0 and its mean and standard deviation are not reported. The posted inferential comparison is between the two instruction groups. It therefore does not provide a statistical estimate of either intervention against control, and it does not answer the full three-group question.

The record does not explain why the control group has no primary-endpoint result. It would be inappropriate to treat the missing value as a measured compliance value of zero or to infer why no endpoint count is listed. The control result is simply not reported as an estimable primary endpoint in the posted summaries.

What is over-dispersion, in general?

In general, over-dispersion means that observed variation is greater than a statistical model expects. It can make standard errors too small and uncertainty appear narrower if the model does not accommodate that extra variability. This study reports standard deviations for the outcome, but the registry does not report a model-based analysis or evidence that over-dispersion was assessed. Because the stated analysis is rank-based, readers should not assume that a particular over-dispersion correction was used.

More broadly, the usefulness of any test depends on its assumptions and the data structure. The record does not give enough detail to evaluate independence, outcome recording, missing observations, or deviations from the intended analysis. These are general considerations for interpreting statistical tests; they are not findings that a specific assumption was violated in this trial.

How do planning illustrations differ from trial results?

Sample-size calculations are planning tools, not observed outcomes or evidence that a study had a particular probability of detecting an effect. The registry’s planning assumptions describe a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with an effect defined as a stated fraction of the observed effect. No sample-size figure is reported in the registry record for interpretation, and the assumptions are explicitly an illustration rather than the trial’s own design justification.

In general, such illustrations depend on the effect selected for planning and on model assumptions. They do not replace a confidence interval for the observed result, and they should not be described as observed power. The trial’s own sample-size justification and any prospective power calculation are not reported in the registry record.

What remains unknown about the analysis?

The registry lists 7 outcome measures and 7 analyses, and names 3 secondary outcomes: questionnaire responses concerning wheelchair discomfort, psychological impacts of assistive devices, and independence in the community. The full analysis methods for those outcomes are not described in the information reported. The record does not state how multiplicity was handled, whether analyses were prespecified, how missing data were treated, whether sensitivity analyses were conducted, or whether any interim analyses occurred.

Those omissions limit assessment of the statistical plan, but they do not invalidate the numbers that are posted. They define the boundary of a responsible interpretation: describe the stated endpoint, analyzed group summaries, and reported test, while leaving unreported methods and results unresolved.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Arm 2: Instruction Group", "Arm 3: Instruction + VSC Group")
n   <- c(10, 6)
m   <- c(8.9, 39.7)
sp  <- c(15.9, 23.5)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Arm 2: Instruction Group  10  8.900  15.900  -2.474  20.274
CARM  Arm 3: Instruction + VSC Group  6  39.700  23.500  15.038  64.362

11. Analyses Reported by the Sponsor

The registry reports the sponsor’s primary comparison as a Wilcoxon (Mann-Whitney) test between the Instruction Group and the Instruction and Virtual Coach Group, with p = 0.27. It also reports group means and standard deviations for those arms. No confidence interval or numerical between-group effect estimate is posted alongside the test result.

No recalculated comparison is reported as estimable from the posted results. The registry also gives no primary-endpoint value for the control group. There is therefore no independent recalculated contrast to set beside the sponsor’s test result, and no basis for replacing that result with a newly calculated estimate. The arm-level means and standard deviations are descriptive summaries and should not be mistaken for the sponsor’s rank-based inferential test.

The registry does not identify a discrepancy between the sponsor’s analysis and a recalculation. The sponsor-reported p-value should be described as the posted inferential result, with its scope limited to the comparison of the two instruction groups. It does not report a comparison with control or establish the magnitude and precision of a group contrast. The analysis details beyond the named method are not reported in the registry record.

12. Multiplicity, Missing Data and Analysis Populations

The registry lists 7 outcome measures and 7 analyses. It identifies 3 secondary outcomes: questionnaire responses concerning the Tool for Assessing Wheelchair Discomfort, the Psychological Impacts of Assistive Devices Scale, and Independence in Community. The primary outcome is compliance rate. The record does not provide a complete description of how these outcomes were ordered, tested, or interpreted as a family of analyses.

When several outcomes or comparisons are examined, the chance of at least one seemingly notable result can increase. In general, multiplicity procedures can address that issue by adjusting inference or by defining a hierarchy of questions in advance. Whether any such procedure was planned or used is not reported in the registry record. The reported p = 0.27 should not be described as adjusted or unadjusted because that detail is not reported.

The record states that the primary endpoint analysis included only participants who completed the study protocol and used the wheelchair. That is an analysis-population description, but the registry does not report how many randomized participants were excluded, the reasons for non-completion, or whether the outcome was available for all eligible participants. The primary-outcome count is n = 10 for instruction and n = 6 for instruction with a virtual coach; the control group is recorded as n = 0 for this endpoint. The relation between these endpoint counts and the 28 enrolled participants is not explained.

Methods for handling missing observations are not reported in the registry record. It is not stated whether missingness was addressed by imputation, complete-case analysis beyond the stated completion requirement, or another method. The record also does not report sensitivity analyses, an intention-to-treat analysis, or the treatment of protocol deviations. These omissions make it difficult to assess how robust the result would be to different assumptions about participants without endpoint data.

Interim analyses, stopping rules, and a full prespecified statistical analysis plan are not reported in the registry record. Their absence from the record should not be read as evidence that they did or did not occur. The posted information supports description of the stated analysis population and outcome summaries, but not a detailed audit of multiplicity or missing-data methods.

13. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The adverse-event record lists no serious adverse events affecting participants in the reported groups. It also lists no other adverse events affecting participants in those groups. The corresponding numbers at risk are 3 for the Control Group, 12 for the Instruction Group, and 13 for the Instruction and Virtual Coach Group.

These safety denominators are not the same as the primary-endpoint analysis counts. In particular, the endpoint record gives n = 0 for control, n = 10 for instruction, and n = 6 for instruction with a virtual coach. The registry does not explain why the adverse-event and endpoint counts differ. The event figures should therefore be interpreted using their own reported denominators rather than substituted for the primary-outcome sample sizes.

The death counts are not reported in the registry record. A blank or unreported death count should not be interpreted as a confirmed count of zero. The registry also does not provide a narrative description of event monitoring, definitions, severity grading, or the period during which adverse events were collected. The absence of listed affected participants is a statement about the posted event figures, not proof that an intervention is free of risk.

Small and differing safety denominators limit how much can be inferred from event counts. The registry’s figures describe the groups and counts it reports; they do not support broader conclusions about safety beyond those observations.

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

The posted result describes change in a defined wheelchair repositioning compliance measure among participants who completed the protocol and used the wheelchair. The two instruction groups had reported mean changes of 8.9 and 39.7, with standard deviations of 15.9 and 23.5, respectively. The registry’s Wilcoxon (Mann-Whitney) comparison between those groups yielded p = 0.27.

These findings do not establish that adding a virtual coach caused a difference in compliance. The reported test does not provide a confidence interval or a numerical estimate of the between-group effect, and the control group has no reported primary-endpoint result. As a result, the posted primary analysis cannot quantify how either instruction approach compared with control. It also cannot establish that the two instruction approaches were equivalent.

In general, a p-value alone does not tell readers whether an observed difference is large enough to matter, nor does it show the range of effects compatible with the data. The absence of a confidence interval and individual-level information leaves uncertainty about the possible size and precision of the group contrast. The reported means summarize analyzed participants, not the full range of individual experiences or the consistency of behavior across measurement periods.

The registry’s analysis population is restricted to protocol completers who used the wheelchair. Without details on the number and characteristics of participants who did not contribute endpoint data, it is not possible to assess whether the analyzed group represents all enrolled or randomized participants. Reasons for absent control endpoint data and the handling of missing observations are not reported in the registry record.

The broader study aims included activity, participation, seating discomfort, and compliance with several clinical practice guidelines. The reported primary result addresses only the specified compliance measure. The registry lists secondary questionnaire outcomes, but their detailed results and analyses are not included in the registry record for this interpretation. The primary compliance result should not be generalized to those other outcomes.

Overall, the registry supports a limited statistical statement: it reports two arm-level means and standard deviations and a rank-based comparison between the two instruction arms, with p = 0.27. It does not supply enough information to determine the precision of the contrast, evaluate the control comparison, or draw conclusions beyond the analyzed compliance outcome.

15. Why This Trial Matters Statistically

This trial is statistically notable because the intervention question has more than one component: instruction was studied alone and with a virtual coach, while a control group was also listed. The posted primary-outcome comparison, however, is only between the two instruction groups. Keeping the design question distinct from the analysis actually reported is essential. A three-group design does not mean that all three comparisons are available in the posted outcome data.

The endpoint is behaviorally specific. Compliance required following a defined position, duration, and frequency and completing a successful repositioning exercise. That definition helps readers understand what the measure represents, while also making the quality and completeness of the underlying event recording important. The registry does not describe those recording procedures in detail.

The trial also illustrates why descriptive summaries and inferential results answer different questions. Means and standard deviations characterize the reported groups, while the Wilcoxon (Mann-Whitney) test evaluates a rank-based comparison. Neither the means alone nor the p-value alone communicates the precision of the contrast. The lack of a confidence interval limits assessment of uncertainty.

Finally, the endpoint counts and listed enrollment do not have a complete account of participant flow in the registry record. The primary outcome is reported for two groups but not control, and the analysis is restricted to protocol completers who used the wheelchair. Those features make it especially important to state exactly which comparison the result addresses and to avoid extending it to the control group or to outcomes without posted results.

The case is a useful reminder that randomized allocation does not by itself resolve questions about missing outcomes, analysis populations, or multiplicity. Those details are part of the evidence needed to interpret a trial’s statistical results, and several are not reported in the registry record.

16. 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 most immediate limitation is that the primary endpoint is not reported for the control group. The study lists three groups, but the posted inferential comparison concerns only instruction versus instruction with a virtual coach. The endpoint record gives control n = 0 and no mean or standard deviation. Thus, the primary results do not show how either intervention group compared with control.

The analysis population was restricted to participants who completed the protocol and used the wheelchair. The record does not explain participant flow, reasons for non-completion, or the relationship between the 28 enrolled participants and the endpoint counts. The results may therefore reflect a subset of enrolled participants, but the extent and consequences of that selection cannot be assessed from the registry record.

The registry provides means and standard deviations for the two instruction groups but no confidence interval or numerical between-group effect estimate. It reports p = 0.27 from a Wilcoxon (Mann-Whitney) test, without the test statistic, detailed implementation, or supporting distributional information. That limits assessment of both the result’s precision and the exact analysis performed.

Further endpoint details are also limited. The record defines compliance and describes measurements every 2 weeks for 8 weeks, with the reported change between baseline and week 7-8, but does not describe event recording, missing measurement handling, protocol deviations, or sensitivity analyses. It does not report whether outcome assessment was masked, despite stating that the study had no masking.

The statistical plan is incomplete in the record. The sample-size justification, trial-specific power calculation, multiplicity method, interim-analysis plan, and detailed prespecification are not reported. The registry lists 7 outcome measures and 7 analyses, but the posted information does not permit a full assessment of how all analyses were interpreted together.

Finally, safety counts have different denominators from the endpoint counts, and death counts are not reported in the registry record. No reasons for the differing counts or detailed safety-monitoring methods are described. These limitations call for a narrow interpretation of the posted primary result, rather than assumptions about unreported methods or outcomes.

17. Related Tutorials

18. Related Statistical Calculators

19. Sources

• ClinicalTrials.gov: Powered Seating Function Usage Among Veterans - Compliance and Coaching — NCT00839098.
• Registry record last updated 2016-02-04; status last verified 2016-01.
• Results first posted 2016-02-04.
• 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.

20. Record Summary

The registry record describes a completed, randomized, parallel-group study with no masking reported, titled “Powered Seating Function Usage Among Veterans - Compliance and Coaching.” It lists 28 enrolled participants and the VA Office of Research and Development as sponsor. The study began in 2011-11, with primary completion in 2013-12.

The primary outcome was compliance with a recommended powered-seat repositioning routine, reported as change from baseline to week 7-8. The analyzed population was limited to participants who completed the protocol and used the wheelchair. The Instruction Group had n = 10, mean 8.9, and standard deviation 15.9; the Instruction and Virtual Coach Group had n = 6, mean 39.7, and standard deviation 23.5. The control endpoint count was n = 0, with no endpoint summary reported.

The registry reports a Wilcoxon (Mann-Whitney) comparison between the two instruction groups, p = 0.27. No confidence interval or control-group endpoint comparison is reported. The record lists 3 secondary outcomes and safety groups with no affected participants reported, while death counts are not reported in the registry record.