Fast-Acting Subperception Study (FAST): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Fast-Acting Subperception Study (FAST) (NCT04231409), a randomized na study. The primary outcome is Overall Pain Responder Rate.

2. Clinical Question

In general, a randomized comparison is intended to assess outcomes between assigned groups while reducing the influence of baseline differences. Here, the registry identifies random allocation, but no primary outcome analysis is reported. The clinical question is therefore clear at the level of the stated endpoint and comparator, but it cannot be answered from the posted results. Further eligibility criteria, baseline pain summaries, and analysis-population details are not reported in the registry record.

3. Trial Design

The registry describes NCT04231409, titled the Fast-Acting Subperception Study (FAST), also called the COMBO Study in its official title. It was a randomized, parallel-group study with no masking. The listed treatment arms were WaveWriter programming and conventional programming, both associated with the Boston Scientific Spectra WaveWriter spinal cord stimulator system. The condition listed was chronic pain, and the study was classified as phase NA.

Enrollment was 41. The record lists the study start as 2019-11-26 and primary completion as 2020-10-01. Its status is terminated. These dates and status describe the registry record; they do not by themselves explain why the study ended. For the primary outcome, the record specifically states that data were not collected and were therefore unavailable because the study was terminated, with follow-up activities affected by COVID-19.

In general, a parallel-group design assigns participants to a programming approach and follows the assigned groups over the same study period. Randomization is intended to support a fair comparison by making assignment independent of participant characteristics on average. It does not guarantee that groups will be balanced, especially in a small study, and it cannot replace outcome data or a transparent analysis.

No detailed randomization procedure, allocation concealment method, masking procedures beyond “none,” or protocol deviations are reported in the registry record. The planned primary outcome time point was 3 months post-randomization. Additional follow-up schedules and analysis procedures are not reported in the registry record. Because the primary measure was not collected, the posted results do not allow assessment of how the assigned programming approaches compared on pain response.

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: Data not collected and hence not available due to termination of the study (Follow-up activities affected by COVID-19)

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 Overall Pain Responder Rate, measured over 3 months post-randomization.

The primary endpoint was the Overall Pain Responder Rate at 3 months post-randomization. It was defined as the proportion of subjects whose average overall pain intensity had fallen by 50% or greater from the Baseline Visit. The registry does not identify the pain-intensity instrument or scale used, and further measurement details are not reported in the registry record.

A responder endpoint converts a continuous change in pain intensity into a yes-or-no classification for each participant: the participant either meets the stated reduction threshold or does not. The proportion of responders then expresses how common that defined outcome was in each group. In general, a responder measure can be easier to interpret clinically than an average score change, because it focuses on reaching a prespecified threshold. It also discards information about how far participants fall above or below that threshold, so it does not describe the full distribution of pain changes.

The threshold and time point define what the endpoint is intended to capture; they do not establish that the outcome was observed. The registry states that the primary outcome data were not collected. Consequently, no responder counts, group proportions, between-group estimate, or uncertainty interval are reported in the registry record. The endpoint's definition can be described, but its observed value and comparative result cannot be assessed.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies a randomized parallel-group design, an unmasked study, a binary responder endpoint, and no reported analyses. It does not report the statistical methods used or a detailed statistical analysis plan. The concepts below are general explanations of how these design and endpoint features are usually interpreted; they are not descriptions of unreported procedures in this study.

What does randomization contribute?

In general, randomization assigns participants to study groups by chance. Its purpose is to reduce systematic differences in prognostic characteristics between groups, so that a comparison of outcomes can be more plausibly attributed to assigned group rather than to the way participants were selected. Randomization does not ensure identical groups, particularly when enrollment is limited. It also does not prevent bias caused by missing outcome data, deviations from assigned treatment, or differences in outcome assessment.

The registry states that allocation was randomized, but the procedure used to generate and conceal allocation is not reported in the registry record. Those details matter because a random sequence and protection against foreknowledge of assignments are distinct elements of sound allocation. The record also states that masking was none. In general, lack of masking can influence expectations, participant reporting, co-interventions, and assessment. The registry does not describe which people knew assignments or how pain outcomes were collected, so the specific pathways to possible measurement bias cannot be assessed.

How should a responder endpoint be understood?

The primary measure classifies participants according to whether their average overall pain intensity decreased by 50% or greater from the Baseline Visit. This is a binary outcome: each participant is counted as a responder or not a responder under the stated rule. A group responder rate is the proportion meeting the definition among participants included in the relevant analysis. The endpoint description does not specify the pain scale, missing-item rules, or handling of participants who did not complete follow-up; these details are not reported in the registry record.

In general, binary outcomes can be analyzed using methods that compare proportions or model the probability of response. The choice of method affects the effect measure and its uncertainty. For example, a report might present group proportions and a difference or ratio, with a confidence interval. None of these estimates or methods is reported for this study's primary endpoint. It would be inappropriate to infer a method from the endpoint label alone.

What does an estimate's uncertainty mean?

In general, a confidence interval communicates the uncertainty around an estimated effect under the assumptions of the analysis. A narrower interval indicates greater statistical precision, while a wider interval indicates less precision. An interval should be interpreted alongside the estimate and the outcome definition; it is not a guarantee that the true effect lies within its endpoints. Here, there is no primary endpoint estimate or interval in the registry record, so neither the direction nor precision of a treatment contrast can be assessed.

A p-value, when reported, is a measure of how compatible the observed data are with a specified null hypothesis under a statistical model. It is not a measure of clinical importance, and it does not establish that the null hypothesis is true or false. No primary endpoint p-value is reported in the registry record. A statement about statistical significance would therefore have no basis in the posted primary outcome results.

Why do missing outcomes matter?

In general, missing data can create bias as well as reduce precision. The consequences depend on why measurements are missing and on how missingness relates to outcomes and treatment group. If follow-up is incomplete, participants with observed outcomes may differ systematically from those without them. Appropriate handling requires information about who was missing, when measurements were missed, and the analysis assumptions. The registry says the primary outcome data were not collected, and attributes their unavailability to termination, with follow-up activities affected by COVID-19. It does not report a missing-data analysis or details that would permit assessment of the missingness pattern.

Because the stated endpoint is not available, there is no observed primary effect to support an effect estimate or its uncertainty. A planning calculation based on a hypothetical target effect would answer a design question, not recover an outcome result. In general, planning illustrations are not observed power and cannot show whether the study's groups differed. The statistical plan, including any planned sample-size justification or interim analyses, is not reported in the registry record.

How should multiplicity be considered?

In general, multiplicity arises when several outcomes, comparisons, time points, or subgroup analyses are tested. Conducting many tests can increase the chance of at least one apparently noteworthy result under a no-effect scenario. Prespecified priorities and suitable adjustment methods can help make interpretation more disciplined. The record lists one outcome measure, but its analysis summary flags several categories or time points and does not reduce it to one comparison. It gives no multiplicity strategy, and no analyses are reported. It is therefore not possible to determine how any potential multiplicity was addressed.

In this record, the main statistical limitation is more fundamental than choosing a model or adjustment: the primary endpoint was not collected. No model can estimate a between-group primary outcome contrast without outcome data. The registry does not report a statistical analysis plan, and the methods that would have been used should not be inferred from common practice.

10. Multiplicity, Missing Data and Analysis Populations

Multiplicity concerns arise in general when an analysis considers several outcomes, contrasts, time points, or subgroups. If many hypotheses are examined, the chance of at least one apparently unusual result can increase. Prespecifying a primary endpoint and comparison, and using an appropriate testing strategy, can help control this issue. The registry lists one outcome measure but its analysis summary notes several categories or time points and does not reduce the outcome to one comparison. The precise intended set of comparisons and any multiplicity approach are not reported in the registry record.

The primary outcome analysis is absent: the record reports zero analyses and says the outcome data were not collected. Thus, there are no reported estimates to evaluate for selective reporting across analyses. The statistical analysis plan, planned interim analyses, and any sample-size justification are not reported in the registry record. They should not be inferred from the randomized design or the stated endpoint.

Missing data are central to interpretation. The record attributes the unavailable outcome data to study termination and says follow-up activities were affected by COVID-19. It does not report how many participants had incomplete follow-up, whether any endpoint observations were collected before termination, or whether missingness differed by group. The endpoint analysis population and missing-data methods are not reported in the registry record. In general, such details are needed to judge whether observed participants could represent all randomized participants. Since no primary outcome data were collected, the posted results cannot establish the impact of missingness on an estimated treatment effect; there is no such estimate.

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 non-serious adverse event terms

The registry reports serious adverse events for the listed safety groups. In WaveWriter Settings, 0 serious adverse events were recorded among 5 participants at risk. In Conventional Settings, 0 were recorded among 4 participants at risk. Deaths were 0 in each group. For other adverse events, the record lists 2 events among 5 participants at risk in WaveWriter Settings and 0 among 4 participants at risk in Conventional Settings.

These are counts as entered in the registry, not a formal comparison of safety between programming approaches. The at-risk counts describe the denominators attached to these entries; they are not the overall enrollment of 41. The record does not report inferential estimates, uncertainty intervals, event timing, severity beyond the serious/non-serious distinction, or whether events were considered related to the device or programming. No serious adverse-event terms are listed.

In general, a zero count in a small safety group does not establish that an event cannot occur or that two groups have equivalent safety. The counts describe what the registry reports for the listed participants and should not be extended beyond that information.

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

The record establishes that a randomized comparison was planned between WaveWriter and conventional programming, with a primary pain-responder outcome assessed at 3 months post-randomization. It also establishes how a responder was defined: a 50% or greater reduction from Baseline Visit in average overall pain intensity. Those details describe the research question, not its answer.

The primary result is not available. The registry says outcome data were not collected and therefore provides no group responder rates or comparative estimate. The record contains no primary-outcome confidence interval or p-value, and reports no analyses. Consequently, the available information cannot establish whether the groups differed, the direction of any difference, or how precisely a difference might have been estimated.

The lack of a reported primary result should not be interpreted as evidence of no effect, equivalence, or failure to reach a threshold. It is also not evidence that a difference existed. The primary endpoint is simply unavailable in the registry record. The record connects this unavailability to termination and notes that follow-up activities were affected by COVID-19, but does not provide the participant-level follow-up details needed to characterize missingness.

The adverse-event entries provide limited descriptive safety information. They include zero serious adverse events and zero deaths in both listed groups, alongside the reported counts for other adverse events. These entries do not constitute a comparative safety analysis and do not establish that the programming approaches have equivalent safety profiles.

In general, randomized assignment can support causal interpretation when outcomes are collected and analyzed appropriately, but randomization alone cannot supply missing results. The registry record supports description of the design, endpoint, termination status, and listed adverse-event counts. It does not support an efficacy conclusion or a definitive comparative safety conclusion.

13. Why This Trial Matters Statistically

This study is statistically important as an example of the distinction between a clearly stated research question and an answerable result. The registry identifies a randomized comparison, a population with chronic pain, two programming approaches, and a responder endpoint with a defined threshold and time point. Yet the primary outcome data were not collected. A complete endpoint definition does not substitute for measurements from participants.

For clinical researchers, the record illustrates why follow-up completion and outcome capture are essential parts of trial design and conduct. In general, missing outcome data affect not only the number of observations available for analysis but also the credibility of comparisons if the reasons for missingness are related to participant outcomes or study groups. The record attributes unavailable data to termination and says follow-up activities were affected by COVID-19; it does not provide details that would allow the pattern or consequences of missingness to be evaluated.

The study also highlights the distinction between design features and statistical evidence. Randomization is a method for assigning participants, not a result. A planned responder measure is not an observed responder rate. Likewise, safety counts can be reported descriptively without establishing comparative safety. Each claim requires the relevant outcome data and an analysis suited to the question.

Finally, registry completeness matters for interpretation. The record provides no primary analysis, statistical plan, or analysis population. Readers can identify what the study intended to compare and why the posted primary result is unavailable, but cannot assess the magnitude or precision of a primary effect. Keeping those boundaries explicit prevents design information from being mistaken for evidence about outcomes.

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.

The most consequential limitation is the absence of primary outcome data. The registry states that data were not collected and were unavailable following termination, with follow-up activities affected by COVID-19. It does not report whether any primary endpoint observations were collected, how many participants were followed, or whether follow-up differed between groups. No primary endpoint estimate is available.

The record gives enrollment of 41 but does not give baseline characteristics, eligibility criteria, group-specific randomized totals, or an analysis population for the primary outcome. The safety entries report smaller at-risk groups, but the registry does not explain how those groups relate to enrollment or why their denominators differ. The pain-intensity scale and further outcome measurement procedures are also not reported in the registry record.

The study is listed as unmasked, but the record does not explain outcome-assessment procedures or who was aware of programming assignments. Programming details for the two arms, allocation procedures, adherence, treatment changes, and protocol deviations are not reported in the registry record. These omissions limit assessment of how the intended comparison was implemented.

The record reports zero analyses and provides no statistical analysis plan, interim analysis information, sample-size justification, missing-data methods, or multiplicity strategy. The primary analysis summary's note about several categories or time points is not accompanied by a detailed account of the intended comparisons. These limitations leave the analysis approach unclear; the missing primary data, however, prevent direct evaluation of the planned endpoint regardless of method.

Safety results are limited to the listed counts and do not include event timing, relatedness, or comparative uncertainty. The record's status is terminated, but further reasons for termination are not reported in the registry record. These constraints mean that efficacy and safety should not be interpreted beyond the descriptive information actually reported.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Fast-Acting Subperception Study (FAST) — NCT04231409.
• Registry record last updated 2022-01-24; status last verified 2022-01.
• Results first posted 2022-01-24.
• 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

NCT04231409 is the Fast-Acting Subperception Study (FAST), also titled the COMBO Study. The registry describes a randomized, unmasked, parallel-group study of WaveWriter and conventional programming of the Boston Scientific Spectra WaveWriter spinal cord stimulator system for chronic pain. Enrollment was 41; the record lists phase NA and status terminated.

The primary endpoint was the Overall Pain Responder Rate at 3 months post-randomization, defined as a 50% or greater reduction from Baseline Visit in average overall pain intensity. The record states that the primary outcome data were not collected, with follow-up activities affected by COVID-19. No primary analyses or comparative result are reported.

Safety entries list 0 serious adverse events and 0 deaths in both groups. Other adverse events are reported as 2 among 5 at risk for WaveWriter Settings and 0 among 4 at risk for Conventional Settings. These are descriptive counts, not a comparative safety analysis.