VELOCITY: A Study to Characterize Real-World Outcomes of Spinal Cord Stimulation: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for VELOCITY: A Study to Characterize Real-World Outcomes of Spinal Cord Stimulation (NCT02741297), a na na study. The primary outcome is Percentage of Low Back Pain Responders.

2. Clinical Question

In general, a single-group real-world study can describe outcomes among participants receiving an intervention, but it cannot by itself distinguish the intervention's contribution from other explanations for change. The registry record states that the objective was to characterize outcomes, not to report a randomized comparison. Consequently, the central statistical question is descriptive: what response was observed in the specified population and timeframe? Because the responder count or percentage is not reported in the registry record, that descriptive question cannot be answered from the posted outcome information.

3. Trial Design

VELOCITY is registered as a completed, single-group study of a device intervention. The listed intervention was the Boston Scientific PRECISION Spinal Cord Stimulator System with MultiWave Technology. The condition is chronic pain, and the study description focuses on chronic intractable pain of the trunk, including unilateral or bilateral pain associated with failed back surgery syndrome or intractable low back pain. Enrollment is listed as 73. The registry lists the phase as not applicable, allocation as not applicable, and masking as none.

The study began on 2016-04-19, reached primary completion on 2018-09-21, and has completed status in the registry record. These dates describe the registered study timeline; they do not establish when each participant entered, received activation, or completed follow-up. Individual follow-up schedules and the timing of participant-level assessments are not reported in the registry record. The primary endpoint specifies assessment three months post-activation.

A single-group design has no concurrent control arm in the registered record. Thus, the observed response—if reported—would describe participants in the study rather than estimate a randomized treatment contrast. Changes over time could reflect multiple influences, and the design does not separate those influences through random allocation. Masking is listed as none, but details about who knew treatment or outcome information at specific stages are not reported in the registry record.

The endpoint population has an additional qualification: it is described as all subjects without outlier sites, with data for sites with outlier subjects removed. The registry does not explain how an outlier site was defined, how many sites were excluded, or how that decision was made. The relationship between the enrollment figure and the endpoint population is therefore not fully described. The sponsor is Boston Scientific Corporation. Other design details, including site count, eligibility criteria, recruitment procedures, and the statistical analysis plan, 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: For " All subjects without outlier sites", data for those sites with outlier subjects were removed.

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 Percentage of Low Back Pain Responders, measured over 3 months.

The primary endpoint is titled Percentage of Low Back Pain Responders. It is a participant-level binary outcome, described as the count of participants, assessed at three months post-activation. A responder must meet the low back pain response criterion and have no increase in opioids from baseline to three months post-activation. The registry record does not specify the pain-response threshold, the pain instrument, or how missing pain or opioid information was handled.

Using a responder definition can make an outcome easier to interpret than a change on a continuous scale: it identifies participants who cross a specified response threshold while also meeting the opioid condition. That convenience depends on a clear, prespecified definition. Different thresholds can classify the same underlying pain changes differently, and a binary outcome does not show how far each participant's result lies above or below the threshold. These are general properties of responder endpoints, not reported findings about this study.

The endpoint is intended to characterize low back pain outcomes while including an opioid-use condition. It does not, by itself, capture every aspect of pain, functioning, quality of life, or treatment burden. Nor does the combined criterion show which component accounts for a participant's responder status. Since no responder count, percentage, or uncertainty estimate is reported in the registry record, the endpoint definition is available but its observed result cannot be interpreted.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a binary primary outcome: participants either meet the responder definition or do not. The specified criterion combines low back pain response at three months post-activation with no increase in opioids from baseline to that assessment. The measure is described as a count of participants, with the outcome title expressing the intended result as a percentage. The registry record does not report the observed count, percentage, or a statistical analysis for this outcome.

What does a binary endpoint represent?

In general, a binary endpoint converts a participant's information into one of two categories according to a rule. This can make a result comparatively straightforward to communicate, particularly when the rule reflects a meaningful threshold. It also discards detail: people just meeting the threshold and people exceeding it substantially are placed in the same category. Interpretation therefore depends on knowing the exact rule and how measurements were collected. For this study, the registry states the opioid condition but does not report the low back pain response threshold or instrument, so the complete classification rule cannot be reconstructed from the record.

How should a percentage and its uncertainty be understood?

In general, a response percentage is an estimate of the share of the analyzed participants who meet the endpoint. Its denominator must be defined: it may be everyone assigned or enrolled, or only those with the required assessment, depending on the analysis. The registry's endpoint population is described as all subjects without outlier sites, with data for sites with outlier subjects removed. The record does not state the resulting endpoint denominator or provide the responder count. Therefore, no response percentage can be checked or interpreted from the information reported.

In general, a confidence interval conveys sampling uncertainty around an estimate. A narrow interval indicates more precision under the method's assumptions; a wide interval indicates less. It does not correct for bias, unclear outcome definitions, or lack of a comparator. No confidence interval for the primary endpoint is reported in the registry record, so neither precision nor compatibility with a range of response levels can be evaluated. No p-value or other inferential result is reported for the endpoint either.

What does the design permit?

The study is registered as single-group, with allocation not applicable and no masking. In general, a single-group outcome can describe the participants' observed experience but does not estimate a randomized difference between intervention and control. A before-and-after assessment, even if one were reported, would not by itself distinguish an intervention effect from other changes over time. The primary endpoint mentions baseline opioid use, but the record does not give a baseline pain result or a comparative analysis. The registry also does not report an adjusted model or other analytic method for the primary endpoint.

Masking is listed as none. In general, knowledge of treatment can influence subjective outcome reporting or assessment, although the extent depends on study procedures. The registry record does not describe who collected or evaluated pain outcomes, or whether any safeguards were used. This does not establish that assessment was biased; it identifies information that would be needed to assess that possibility.

What do the planning assumptions mean?

The registry material describes a sample-size planning illustration based on an observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It states that the effect to detect is a stated fraction of the observed effect. Such assumptions describe a hypothetical planning exercise, not the design of this registered single-group study, and they do not supply a result for the primary endpoint. No calculated planning sample sizes or observed effect used for those calculations are reported in the registry record.

In general, a planning calculation asks what sample size might be needed to detect a specified effect under stated assumptions. It is not an estimate of the probability that a completed study's finding is true, and it is not observed power. A calculation that uses an observed effect as its starting point is especially dependent on that estimate and its uncertainty. Here, the planning assumptions do not replace a missing responder result, and they do not establish that the study was designed as a two-arm comparison.

Why can over-dispersion matter?

In general, over-dispersion arises when observed variation is greater than a statistical model expects. It can make standard errors too small and intervals or tests too optimistic if the model does not allow for that extra variation. This concept is relevant to some count or clustered data analyses, but the registry's primary endpoint is a participant count for a binary responder outcome, and no model or variance estimate is reported. There is no basis in the registry record to determine whether over-dispersion was assessed or relevant to the sponsor's analysis.

The registry lists one outcome measure and zero analyses. That means no primary endpoint analysis result is available in the record. The analytic population, treatment of missing data, any covariate adjustment, and handling of site-level variation are not reported in the registry record. These omissions limit independent appraisal of the endpoint beyond its stated definition and timeframe.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists one outcome measure, identifies it as the primary endpoint, and lists zero analyses. A multiplicity strategy is not reported in the registry record. In general, multiplicity arises when several hypotheses or outcomes are tested; repeated testing can increase the chance of at least one apparently positive result by chance. Prespecified testing hierarchies or adjustments can address particular multiplicity concerns, but the record does not describe such a plan. The listed outcome count alone does not establish which analyses may have been planned or performed outside the registry entry.

Missing-data handling is not reported in the registry record. This matters because the endpoint requires an assessment at three months post-activation and opioid information spanning baseline to that assessment. If either component is unavailable, the registry does not say whether the participant would be classified as a nonresponder, excluded from the endpoint analysis, or handled another way. These choices can affect the numerator, denominator, and interpretation of a responder estimate. No missingness counts or sensitivity analyses are reported.

The analysis population is described as all subjects without outlier sites, with data for sites with outlier subjects removed. The record does not define an outlier site, report the number of sites or participants affected, or explain whether the exclusion was prespecified. It also does not identify an intention-to-treat or per-protocol analysis population. Accordingly, the extent and potential effect of exclusions cannot be assessed from the registry record.

In general, clear reporting of missing-data rules and analysis populations helps readers understand which participants contribute to an estimate and how robust it may be. Without these details—and without a posted endpoint estimate—neither the direction nor magnitude of any potential influence can be determined.

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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: angina unstable (1.4%), coronary artery disease (1.4%), flank pain (1.4%), tenosynovitis (1.4%), constipation (1.4%).

The registry lists safety information for the Spinal Cord Stimulation System group. Serious adverse events affected 6 participants, with 73 at risk. Other adverse events affected 4 participants, also with 73 at risk. Deaths are listed as 0. These are participant counts in the registry record; they should be read as separate summaries, not added together. The record does not state whether the participants in the two adverse-event categories overlapped.

The serious-event terms listed with frequencies are Angina Unstable, Coronary Artery Disease, Flank Pain, Tenosynovitis, Constipation, and Hepatitis, each reported as 1.4%. These term frequencies describe the registry's event listings. The record does not provide additional context about event timing, severity beyond the serious classification, recurrence, or attribution to the intervention. It therefore cannot establish from these figures whether an event was caused by stimulation or the device.

In general, adverse-event counts describe events observed and recorded under a study's collection procedures; they do not by themselves establish comparative risk. With a single-group study and no control comparison reported, the figures do not quantify excess risk relative to another treatment or to no intervention. The registry record does not report a detailed safety analysis, exposure-adjusted rates, or a causal assessment.

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

The study record identifies an effort to characterize real-world outcomes of spinal cord stimulation for chronic intractable pain, with a primary endpoint focused on low back pain responders at three months post-activation. It also provides a safety summary for the intervention group. However, the primary responder count and percentage are not reported in the registry record, and the record lists zero analyses. Readers therefore cannot determine the observed response frequency, its precision, or whether the endpoint criterion was met by any particular share of participants.

The design also shapes what any outcome could mean. VELOCITY is listed as single-group, with no allocation and no masking. In general, a single-group description can document what happened among participants receiving the intervention, but it does not supply a randomized comparison that separates intervention effects from other explanations. The registry record does not report a control group or comparative outcome. It would therefore be inappropriate to treat the study description as proof that the intervention caused a change, or as a comparison of its outcomes against another option.

The responder definition combines pain response with no increase in opioids. That combination may be useful for describing a particular treatment goal, but the pain threshold and measurement instrument are not reported. A responder classification cannot be independently interpreted without knowing those details. Nor does a binary endpoint convey the full range of pain experiences or other outcomes that may matter to participants.

The safety counts show that serious and other adverse events were recorded, and the registry lists no deaths. They do not establish causality or comparative safety. In general, safety interpretation depends on definitions, ascertainment, follow-up, and an appropriate comparator; those details are not fully reported in this registry record.

Thus, the record supports a description of study purpose, design, endpoint definition, and selected safety counts. It does not support a quantitative conclusion about the primary outcome or a causal conclusion about benefit or harm. Missing outcome results should not be mistaken for either a favorable or an unfavorable result.

13. Why This Trial Matters Statistically

This study is statistically notable because its stated aim is to characterize real-world outcomes while using a defined responder endpoint. Such endpoints can communicate outcomes in a form that is readily understood, but they require transparent definitions and complete reporting. Here, the registry gives the timeframe and opioid condition but does not report the pain-response threshold or instrument. It also does not report the responder estimate. The distinction between an endpoint being registered and its result being available is important: a clearly named outcome is not itself evidence about the outcome.

The single-group design is also central to interpretation. In general, a real-world description may provide information about outcomes under the conditions in which care was delivered, but the absence of a control group limits causal attribution. This distinction matters when readers move from asking what was observed to asking what was caused by treatment. A design can address the first question without resolving the second.

The registry's exclusion of data from sites with outlier subjects raises a reporting issue. Exclusions can be consequential when they determine which observations contribute to an endpoint. The record does not define the outlier rule or describe how many sites or participants were affected, so the population represented by the primary endpoint cannot be fully assessed.

Finally, the registry lists safety counts but no primary outcome analysis. Statistical interpretation requires both an estimate and enough information to understand its uncertainty and construction. The absence of those elements prevents assessment of response frequency and precision. This case illustrates why trial design, outcome definitions, analysis populations, missing-data procedures, and posted results all contribute to a complete statistical account—not merely the enrollment figure or the study's stated objective.

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.

Several limitations specific to this registry record constrain interpretation. The primary endpoint result is not reported: there is no responder count, percentage, or uncertainty estimate. The record lists zero analyses, so there is no posted statistical result against which to evaluate the study objective. This prevents assessment of the frequency and precision of the defined response.

The endpoint's pain-response threshold and measurement instrument are not reported. Although the opioid condition and assessment timeframe are described, the full responder rule cannot be reproduced from the registry information. Missing-data procedures for the pain and opioid components are also not reported, and the number of participants contributing to the endpoint is not stated.

The endpoint population excludes data from sites with outlier subjects, but the outlier definition, number of affected sites, number of affected participants, and rationale for removal are not reported. This makes it difficult to judge how the endpoint population relates to the enrolled population. The analysis population label and any sensitivity analysis are not reported either.

The study is single-group, with allocation not applicable and masking listed as none. No concurrent comparator is reported, limiting causal interpretation. Details about treatment delivery, outcome assessment, and the role of site-level variation are not reported in the registry record. The registry also does not report a multiplicity plan, statistical model, or missing-data analysis. These gaps do not prove that procedures were absent; they indicate that they cannot be evaluated from the record.

The adverse-event information is limited to participant counts, deaths, and selected serious-event terms. The registry does not report comparative safety estimates or establish event attribution. Taken together, the available record documents the study's purpose and selected design and safety features, but leaves the primary efficacy-style outcome and several details needed for independent statistical appraisal unavailable.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: VELOCITY: A Study to Characterize Real-World Outcomes of Spinal Cord Stimulation — NCT02741297.
• Registry record last updated 2021-01-05; status last verified 2020-12.
• Results first posted 2020-01-10.
• 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

VELOCITY (NCT02741297) is a completed, single-group study of the Boston Scientific PRECISION Spinal Cord Stimulator System with MultiWave Technology for chronic pain. Enrollment is listed as 73. The registered primary endpoint is the percentage of low back pain responders at three months post-activation, requiring no increase in opioids from baseline. Its population excludes data from sites with outlier subjects.

The registry lists no allocation, no masking, one outcome measure, and zero analyses. The primary responder result is not reported in the registry record. Safety information lists 6 participants affected by serious adverse events and 4 affected by other adverse events, with 0 deaths. The record does not establish event attribution or provide a control-group comparison. The study dates are 2016-04-19 to primary completion on 2018-09-21, and the sponsor is Boston Scientific Corporation.