Impact of Pushrim Activated Power Assist Wheelchairs on Mobility Among People With Tetraplegia: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Impact of Pushrim Activated Power Assist Wheelchairs on Mobility Among People With Tetraplegia (NCT00281463), a na na study. The primary outcome is Oxygen Consumption.

2. Clinical Question

The broad aim was to evaluate the PAPAW across a three-phase study. The description says Phase I would examine steady-state metabolic energy efficiency while propelling a manual wheelchair with and without the device. Phase II would assess usability and acceptability over an activities-of-daily-living course and identify areas for future development. Phase III would compare community activities of daily living using participants’ personal wheelchairs and a PAPAW. These are aims in the study description; the registry record does not report phase-specific findings or confirm which assessments were completed.

The primary endpoint listed for the record is narrower than that broad program of work: it concerns oxygen consumption in a laboratory dynamometer setting. It does not, by itself, represent every usability, acceptability, or community-mobility question described in the study summary.

3. Trial Design

The registry classifies this as a completed, single-group study with an enrollment of 45. Allocation is recorded as NA, and masking is recorded as none. The record identifies the intervention as a device, the Pushrim Activated Power Assist Wheelchair. It does not describe random assignment to separate groups.

The arm description states that participants would propel both their own chair and a pushrim activated power assist wheelchair on a computer-controlled wheelchair dynamometer. That wording indicates the intended assessment involved both chairs, but the registry record does not report whether every participant completed both assessments, how the order was determined, or how the two sets of measurements were analyzed. The study is categorized as single-group, so the personal-chair assessment should not be read as a separately randomized control arm.

The study summary describes three phases: laboratory metabolic-efficiency assessment, evaluation on an activities-of-daily-living course, and comparison of community activities of daily living. The registry record does not provide phase-specific enrollment, completion, or analysis details. It also does not clarify whether the primary oxygen-consumption outcome was collected for all phases or only for the in-lab assessment named in its timeframe.

The recorded start is 2001-11, and primary completion is 2007-03. The overall status is completed. The listed phase is NA. The registry record does not report a more detailed protocol timeline, a recruitment setting, or further design specifications. These omissions limit what can be reconstructed about the practical conduct of the study from the registry entry alone.

Because the design is single-group and the stated assessment involves each participant’s own wheelchair and a PAPAW, interpretation depends on details such as measurement order, the number of complete paired observations, and the analysis method. Those details are not reported in the registry record. The design label and arm description establish the broad structure, but they are not enough to determine how potential order effects or incomplete measurements were handled.

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: personal w/c (.9 m/s, 10 W)

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 Oxygen Consumption, measured over in-lab visit when propelling on a computer controlled wheelchair dynamometer.

The primary outcome is oxygen consumption, with the unit recorded as VO2 (ml/min). The registry identifies the summary parameter as a mean and the measure of dispersion as a standard deviation. The stated timeframe is an in-lab visit when propelling on a computer-controlled wheelchair dynamometer. The population detail specifies personal w/c (.9 m/s, 10 W).

Oxygen consumption is a physiological measure of the oxygen used during activity. In general, researchers may use it to characterize the metabolic demand associated with performing a task. For a wheelchair-propulsion assessment, it can therefore provide information about the energy demand observed under the specified testing conditions. This is a general explanation of the measure; it does not establish what the study found.

The registry record does not report a mean, standard deviation, sample size for this endpoint, or an estimate comparing the personal wheelchair with the PAPAW. It also does not state a threshold for a meaningful difference or specify how steady state was defined for the reported outcome. Without those details and the outcome values, the direction, magnitude, and precision of any difference cannot be assessed from the registry record.

The endpoint is a laboratory measure rather than a direct report of community mobility, device acceptability, or activities of daily living. Those broader topics appear in the study summary, but the oxygen-consumption endpoint alone does not answer all of them.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a continuous primary outcome summarized by a mean and standard deviation. The outcome is oxygen consumption in VO2 (ml/min). No numerical result or inferential analysis is listed, so the statistical methods can be explained only in general terms and in relation to the design description.

What does a mean describe?

In general, a mean is a measure of the center of a set of numerical observations. For this endpoint, it would describe the average oxygen-consumption value among the observations included in an analysis. A mean does not show how values are distributed around the center, whether measurements are unusually spread out, or whether all enrolled participants contributed data. That is why the registry also names a standard deviation as the dispersion measure, while not reporting its value.

What does the standard deviation describe?

In general, the standard deviation describes the spread of individual observations around their mean. It is not the same as the uncertainty in the estimated mean or the uncertainty in a difference between conditions. A confidence interval is commonly used to express uncertainty in an estimate: it gives a range of values compatible with the data and the method used, under the assumptions of that method. The registry record does not report a confidence interval for this outcome or comparison.

How does the study structure affect analysis?

The record identifies a single-group study and says participants would propel both their own chair and a PAPAW. If measurements from both chairs were obtained from the same participant, the observations would be related rather than independent. In general, a paired analysis accounts for this relationship by analyzing within-participant differences. A separate-group analysis instead treats observations in each group as coming from different participants. The registry record does not state which method was used, whether all intended paired measurements were available, or whether a formal comparison was conducted.

That distinction is not merely technical. An analysis that ignores the relationship between repeated measurements can misstate uncertainty. Conversely, it is not possible to claim that a paired analysis was used merely because participants were asked to propel both chairs. The analysis plan and results are not reported in the registry record.

Why do testing conditions matter?

The endpoint is tied to an in-lab visit using a computer-controlled wheelchair dynamometer. The recorded population detail specifies the personal wheelchair at .9 m/s and 10 W. In general, measurement conditions define the context to which an estimate applies. A result under a particular laboratory workload would describe oxygen consumption under those test conditions, rather than all wheelchair use in daily life. The registry record does not provide further information on the test protocol, measurement repetitions, or how the laboratory condition was maintained.

What can a p-value and confidence interval contribute?

In general, a p-value summarizes how inconsistent the observed data are with a specified null hypothesis under a statistical model. It is not the probability that the null hypothesis is true, and it does not measure the size or practical importance of an effect. A confidence interval complements an estimate by expressing its uncertainty and the range of values compatible with the analysis. Neither can be interpreted for this primary outcome because no p-value, confidence interval, or analysis estimate is reported in the registry record.

How should planning illustrations be read?

The registry’s planning assumptions describe a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. They state that the effect to detect is a specified fraction of the observed effect. These are planning assumptions, not evidence that the trial used that design: the registry classifies the study as single-group, and the calculation is explicitly described as a planning illustration rather than the trial’s own design.

In general, a sample-size calculation estimates how many observations a proposed study might require under selected assumptions about the effect, variability, significance level, allocation, and analysis. It does not indicate what was observed, and a planned power value is not observed power. The assumptions named in the record do not supply the missing outcome means, standard deviations, or comparison estimate. No numerical sample-size illustration is stated in the registry entries used for this explanation.

The planning description refers to participants per arm for non-time-to-event calculations and total events for time-to-event calculations. The primary outcome in this record is continuous, and the study is classified as single-group. The two-arm illustration therefore should not be mistaken for a description of the actual trial allocation. It is a hypothetical planning framework, not a report of the trial’s analysis.

Why does over-dispersion matter in general?

For outcomes whose variability is greater than a statistical model assumes, uncertainty estimates can be too small if that extra variation is ignored. This is often called over-dispersion. It is a general issue for some types of data and models; it is not reported as a feature of this continuous oxygen-consumption outcome. The registry record does not identify a model, a dispersion adjustment, or any diagnostic assessment, so no claim about over-dispersion in this study is warranted.

In short, the record identifies the outcome scale, summary statistics intended, and broad measurement setting, but does not report the analysis method or inferential results. A precise statistical interpretation would require those missing details alongside the endpoint values.

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("Pushrim Activated Power Assist Wheelchair")
n   <- c(15)
m   <- c(625)
sp  <- c(316)
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  Pushrim Activated Power Assist Wheelchair  15  625.000  316.000  450.005  799.995

11. Multiplicity, Missing Data and Analysis Populations

The study summary describes several objectives across three phases: metabolic energy efficiency, usability and acceptability on an activities-of-daily-living course, and community activities of daily living. The registry lists 2 outcome measures, but the additional measure is not described in the registry record for this account. A hierarchy among outcomes, a plan for controlling multiplicity, and any adjustment for multiple comparisons are not reported in the registry record.

In general, testing multiple outcomes or comparisons can increase the chance of finding an apparently notable result by chance. A prespecified hierarchy or multiplicity adjustment can help clarify how evidence across several tests should be interpreted. The registry record does not report whether either approach was planned or used, so it is not possible to assess how multiple aims were handled statistically.

The registry lists 0 analyses and provides no analysis population for the oxygen-consumption outcome. It does not report missing-data counts, reasons for missingness, an imputation method, or a sensitivity analysis. Enrollment of 45 should not be treated as the number with complete endpoint data. The record also does not state whether participants who did not complete a measurement were included in any analysis or how incomplete paired measurements would have been handled.

These omissions leave uncertainty about the relationship between the enrolled population and any analyzed population, as well as about the robustness of results to missing observations. They do not show that data were missing or that a particular method was omitted from the full study protocol; those details are simply not reported in the registry record.

12. 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 entry lists one group, the Pushrim Activated Power Assist Wheelchair group, with 45 participants at risk for serious adverse events and 0 affected. It also lists 45 at risk for other adverse events and 0 affected. No serious adverse-event terms are listed.

These figures describe what the registry reports for the listed group. They do not establish the completeness or duration of adverse-event collection, and the record does not provide event definitions, collection procedures, or a comparison group. The at-risk counts should not be interpreted as proof that all 45 enrolled participants completed the same period of follow-up.

The death field is null, so a death count is not reported in the registry record. A null entry is not a reported zero. The zero counts for serious and other adverse events can be stated as recorded, but the available information does not allow a broader assessment of safety or a comparison between wheelchair conditions.

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

The registry record establishes that the study was intended to evaluate a Pushrim Activated Power Assist Wheelchair and that oxygen consumption was the primary listed outcome. It identifies a laboratory dynamometer setting, a mean and standard deviation as the intended summaries, and a single-group design. It also describes broader aims involving usability, acceptability, and community activities of daily living.

However, the registry record does not report numerical oxygen-consumption results, a comparison estimate, a confidence interval, or a p-value. It therefore does not show whether oxygen consumption was higher, lower, or similar under the two wheelchair conditions, nor how precisely any difference was estimated. The description of an intended assessment is not evidence of an observed effect.

Even a numerical laboratory result would address the tested conditions and endpoint. It would not, by itself, answer questions about everyday mobility, long-term use, user preferences, or all of the activities-of-daily-living aims in the study summary. Those are distinct outcomes and contexts. Their findings are not reported in the registry record.

The single-group classification and the description of participants using both their own chair and a PAPAW also matter. Without details of measurement order, completion, and analysis, the record does not establish how a comparison between chair conditions was estimated. The enrollment figure of 45 does not indicate how many observations were available for the primary analysis.

Accordingly, the defensible reading is limited: the registry documents a completed study with a stated device, design, and primary measurement, but does not provide the outcome results needed to judge the size, direction, or precision of a difference. No conclusion about treatment benefit or lack of benefit follows from the absence of registry results.

14. Why This Trial Matters Statistically

This study is statistically notable for the relationship between its broad aims and its listed primary endpoint. The study summary spans metabolic efficiency, usability and acceptability, and community activities of daily living. The primary outcome recorded in detail is oxygen consumption during a laboratory dynamometer visit. These represent different kinds of questions, and the endpoint should be interpreted within its stated measurement context.

The single-group design also makes the comparison structure important. Participants were described as propelling both their personal wheelchair and a PAPAW, while the registry classifies the study as single-group rather than as a randomized comparison. In general, repeated measurements on the same participant require attention to their within-person relationship. The registry does not report the analysis method, so it cannot establish how that relationship was handled.

The record illustrates why enrollment and analysis sample size are not interchangeable. Enrollment is 45, but the number contributing primary-outcome data is not reported. Without endpoint-specific counts and variability, the precision of a mean or comparison cannot be judged. A study’s design description alone cannot substitute for its results.

Finally, planning calculations and observed findings answer different questions. The stated planning framework uses assumptions for a hypothetical two-arm calculation, while the actual registry design is single-group. Such planning illustrations can describe requirements under assumptions; they cannot serve as trial findings or as observed power. Distinguishing design, planning, and results is essential when interpreting a registry entry with no listed analyses.

15. 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 statistical interpretation is that the registry record does not report the primary outcome values or any analysis results. No mean, standard deviation, comparison estimate, confidence interval, or p-value is available. This prevents assessment of effect direction, magnitude, and precision.

The design description is also incomplete for reconstructing the comparison. Participants were asked to propel both their own chair and a PAPAW, but measurement order, completion of both assessments, and the analysis approach are not reported in the registry record. The record does not provide endpoint-specific participant counts or missing-data information, so the enrolled total cannot be assumed to equal the analyzed total.

The study summary describes three phases and multiple areas of interest, but the record does not report phase-specific results, outcome hierarchy, or multiplicity procedures. It also does not explain how the primary laboratory endpoint relates to the broader activities-of-daily-living aims. Consequently, the listed endpoint cannot stand in for unreported usability or community-mobility results.

Further limitations include the absence of detailed eligibility criteria, participant characteristics, measurement procedures, and analysis-population definitions in the available the registry entries. Safety reporting is limited to the listed event counts, with no event-collection details and no reported death count. These gaps restrict interpretation of both the study conduct and the completeness of the posted results; they do not establish what the full study protocol or other records may contain.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Impact of Pushrim Activated Power Assist Wheelchairs on Mobility Among People With Tetraplegia — NCT00281463.
• Registry record last updated 2014-11-18; status last verified 2014-11.
• Results first posted 2014-11-18.
• 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.

19. Record Summary

NCT00281463 is a completed single-group study titled “Impact of Pushrim Activated Power Assist Wheelchairs on Mobility Among People With Tetraplegia.” The sponsor is VA Pittsburgh Healthcare System. Enrollment is recorded as 45, with a start of 2001-11 and primary completion of 2007-03. Allocation is NA, masking is none, and the listed phase is NA.

The intervention is a Pushrim Activated Power Assist Wheelchair. Participants were described as propelling both their personal wheelchair and a PAPAW on a computer-controlled wheelchair dynamometer. The primary outcome is oxygen consumption, VO2 (ml/min), summarized as a mean with standard deviation during an in-lab visit; the recorded personal-wheelchair condition is .9 m/s and 10 W.

The registry lists 2 outcome measures and 0 analyses. Numerical primary-outcome results and the analysis details are not reported in the registry record. The adverse-event entry records 0 affected for serious and other adverse events among 45 at risk in the listed group; a death count is not reported.