Fibromyalgia Activity Study With Transcutaneous Electrical Nerve Stimulation (FAST): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Fibromyalgia Activity Study With Transcutaneous Electrical Nerve Stimulation (FAST) (NCT01888640), a randomized na study. The primary outcome is Pain Rating With Movement (0-10 Low to High Scale) During Six Minute Walk Test.

2. Clinical Question

The registry’s stated hypothesis was that TENS would reduce resting and movement-related pain and central excitability, and that changes in pain or central excitability would be associated with reduced fatigue and fear of movement and improved function and quality of life. These are hypotheses, not reported findings. The primary endpoint specifically concerns pain during movement, rather than resting pain or the broader set of symptoms and functional measures listed as secondary outcomes.

The registry record identifies the primary endpoint and its planned assessment times, but does not report the group means, changes, confidence intervals, or post hoc comparison p-values. It therefore does not permit a numerical answer to the clinical question. The record describes the question being investigated, not evidence establishing whether the hypothesized changes occurred.

3. Trial Design

The FAST study is registered as a randomized, double-masked, parallel trial of TENS for fibromyalgia. Its recorded status is completed. The registry lists enrollment of 301 and records the phase as NA. The study start date is 2013-09-30, and the primary completion date is 2018-04-02. The registry record does not explain the meaning of the phase entry or give further details about masking.

Three groups were randomized for the first four weeks: active TENS, placebo TENS, and no TENS with standard care. The active-TENS group continued active treatment for an additional four weeks. The placebo-TENS group received placebo during the first four weeks and active TENS during the final four weeks. The no-TENS group had no TENS intervention during the first four weeks, while completing the testing procedures, and then received active TENS during the final four weeks. Thus the randomized comparison is focused on the initial four-week period; the later assessment takes place after all groups have received active TENS.

The primary endpoint was assessed at baseline, at four weeks after randomization, and at eight weeks. The registry describes the four-week analysis as the randomized phase and the eight-week measure as change from baseline when all groups received active TENS. It also states that the intention-to-treat analysis was corrected for differences between the Iowa and Vanderbilt sites. Post hoc comparisons between groups are described, but their results are not reported in the registry record.

The registry lists TENS as a device intervention and names Kathleen Sluka as sponsor. It does not report the details needed to reconstruct allocation procedures, the masking implementation, adherence, or the sample-size justification. Those features should not be inferred from the general design labels.

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:

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 Pain Rating With Movement (0-10 Low to High Scale) During Six Minute Walk Test, measured over Time Frame: Baseline (Visit 2), 4 weeks (Visit 3, randomized to 3 groups), and 8 weeks (Visit 4, all groups home TENS.

The primary endpoint is pain with movement during the six-minute walk test, rated on a numeric scale from 0 to 10, with higher values indicating more pain. It captures pain reported while participants perform a walking task, rather than pain at rest. A movement-related measure is relevant to the study’s stated interest in pain that may affect daily function and activity.

The registry describes the endpoint as a mean change from baseline at the four-week and eight-week visits. At four weeks, participants had been assigned to active TENS, placebo TENS, or no TENS. At eight weeks, all groups had received active TENS during the final four weeks. The reported analysis plan specifies adjusted 95% confidence intervals and says that p-values represent post hoc comparisons between groups. The intention-to-treat analysis was corrected for site differences between Iowa and Vanderbilt.

In general, a mean change describes the average direction and magnitude of change in the measured score from baseline. A confidence interval conveys uncertainty around an estimated value under the analysis assumptions; it is not a range guaranteed to contain every participant’s response. Because the numerical endpoint estimates, confidence intervals, and p-values are not reported in the registry record, the amount of change and its precision cannot be described. The endpoint definition alone does not establish that pain changed or that any change was attributable to TENS.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies a randomized, double-masked, parallel design. Randomization is intended to make assigned groups comparable on average, while masking is intended to reduce the influence of knowledge of treatment assignment on care or assessment. These are general purposes of the design features; the registry record does not describe how randomization or masking was implemented, who was masked, or whether masking was maintained.

What does the mean change represent?

The primary measure is a continuous pain score from 0 to 10 during the six-minute walk test. The planned summaries are mean changes from baseline. A mean gives a group-level description of the scores; it does not show how much individual participants varied or whether every participant changed in the same direction. The numerical group means and changes are not reported in the registry record.

Why report confidence intervals?

The endpoint description specifies adjusted 95% confidence intervals. In general, a confidence interval expresses uncertainty around an estimate under the statistical model and assumptions used. A narrower interval indicates greater precision than a wider interval, all else being equal. An interval should be considered alongside the size and meaning of the estimate, not treated as a statement about the proportion of individual participants whose scores fall within it. Since the intervals themselves are not reported, their precision cannot be judged.

What does adjustment for site mean?

The registry says that the intention-to-treat analysis was corrected for differences between the Iowa and Vanderbilt sites. In general, accounting for site can help separate site-related differences in outcomes from the treatment-group comparison. The record does not specify the model, the adjustment details, or the extent of any site differences. It is therefore not possible to reproduce or further assess the adjustment from the registry description alone.

How should the p-values be read?

The primary endpoint description says that p-values represent post hoc comparisons between groups. In general, a p-value summarizes how compatible the observed data are with a null hypothesis under a statistical model. It is not the probability that the null hypothesis is true, and it does not indicate the magnitude or clinical importance of a difference. The actual p-values and the comparisons to which they apply are not reported in the registry record.

Why does over-dispersion matter?

General statistical context: for count outcomes, over-dispersion means that the observed variability exceeds what a simple count model assumes. A model that does not account for extra variability can give confidence intervals that are too narrow and p-values that are too small. The primary endpoint in this study is a continuous pain score, not a count outcome, and the registry record does not report an over-dispersion analysis. This concept does not establish anything about the results of this trial.

What can be inferred from the sample-size assumptions?

The registry describes a 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 says that the effect to detect is a stated fraction of the observed effect and distinguishes participant-per-arm illustrations from total-event calculations for time-to-event outcomes. Such illustrations are planning calculations, not observed power and not evidence that the trial was designed using those assumptions. The registry record does not report a sample-size justification for the trial, and the observed effect needed to interpret such an illustration is not reported in the primary outcome details.

The registry lists 16 outcome measures and 32 analyses. These counts do not reveal the analysis model for each outcome, the prespecified hierarchy of tests, or whether multiplicity adjustments were used. The number of analyses alone cannot determine the risk of false-positive findings or the reliability of any particular comparison. Those details are not reported in the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 16 outcome measures and 32 analyses, including the primary movement-related pain measure and secondary outcomes for resting pain, fatigue, fibromyalgia impact, and pain interference and intensity. Multiple outcomes and group comparisons create a general multiplicity concern: when many hypotheses are tested, the chance of at least one apparently unusual result can increase unless the analysis plan accounts for the testing structure. The registry record does not report whether a multiplicity adjustment was used, which comparisons were prespecified, or whether any hierarchy governed interpretation. It would be inappropriate to assume either that adjustments were or were not made.

The primary endpoint description identifies post hoc comparisons between groups, but the registry record does not report which comparisons were performed or their numerical results. It also does not report an interim-analysis plan. The absence of that information in the registry record is not evidence that a particular procedure did or did not occur.

The primary outcome description labels the analysis intention-to-treat and says it was corrected for site differences. The record does not define the analysis population further, give participant flow for the primary endpoint, or report how missing observations were handled. It does not state whether imputation, a complete-case approach, or another method was used. Missing-data methods matter because conclusions can depend on why observations are missing and how the analysis accounts for them. Without those details, the robustness of the endpoint estimates to missing data cannot be assessed.

The record describes the randomized four-week comparison and an eight-week assessment after all groups received active TENS. These phases answer different questions and should not be treated as interchangeable. The numerical results and fuller analysis plan are not reported in the registry record, so multiplicity, missing-data handling, and the exact scope of the analysis populations remain uncertain.

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 2% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: chest pain (1.0%), dehydration and gastrointestinal pain (1.0%), depression (1.0%).

For the randomized groups, the registry reports serious adverse events affecting 0 of 103 participants in the active-TENS group, 1 of 99 in the placebo-TENS group, and 2 of 99 in the no-TENS (standard care) group. It reports deaths of 0 in each of those groups. These are counts of participants affected, not measures of treatment effect. The record also lists a pre-randomization category, with 1 serious adverse event among 352 at risk and 0 other adverse events among 352 at risk; this category is not one of the randomized treatment groups.

The registry lists chest pain, dehydration and gastrointestinal pain, and depression among the top serious event terms, each reported as 1.0%. It does not provide further event-level detail in the registry record for this account. The other adverse-event counts reported for the randomized groups are 12 of 103 for active TENS, 10 of 99 for placebo TENS, and 15 of 99 for no TENS (standard care). Those counts should not be conflated with the serious-event counts.

In general, adverse-event counts describe events recorded during the study and do not establish that an intervention caused them. They also do not, on their own, show whether groups differ reliably; that assessment requires appropriate comparisons and fuller context. The registry record does not report event definitions, severity details beyond the serious-event classification, exposure-adjusted rates, or a comparative safety analysis. The counts therefore provide a limited descriptive account, not a causal safety conclusion.

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

The registry record establishes that FAST was a randomized, double-masked, parallel study of TENS for fibromyalgia and identifies movement-related pain during a six-minute walk test as its primary endpoint. It also describes how the treatment conditions changed over the study: the groups differed during the first four weeks, and all groups received active TENS during the final four weeks. These registry entries clarify the question the study was designed to address.

The record does not report numerical primary endpoint results. It therefore does not show whether the average pain score changed, how large any change was, how precise an estimate was, or whether group comparisons were statistically distinguishable. The stated hypothesis about pain, central excitability, fatigue, fear of movement, function, and quality of life should not be mistaken for a finding. No conclusion that TENS does or does not work follows from the endpoint description or the study design alone.

Even if numerical changes from baseline were available, interpretation would depend on the relevant comparison. The randomized four-week period compares different assigned conditions. At eight weeks, all groups had received active TENS during the final four weeks, so a baseline change at that visit would not by itself separate treatment effects from changes associated with time or other influences. The registry’s description does not supply the numerical estimates needed to interpret either phase.

The serious and other adverse-event counts are descriptive and do not establish causation. The registry record also lacks details needed to assess missing data, multiplicity, and the exact analysis procedures. Consequently, the most defensible reading is limited: the record documents a trial design and planned outcome assessment, but does not provide enough primary outcome information for an estimate of benefit, harm, or statistical precision.

13. Why This Trial Matters Statistically

FAST is statistically notable for distinguishing a randomized comparison from a later assessment in which all groups received active TENS. The four-week phase compares three assigned conditions, while the eight-week visit follows active TENS in every group during the final four weeks. Recognizing that change in exposure is important: a randomized contrast during the first phase and a change from baseline during the later phase do not answer the same question.

The primary endpoint also focuses on pain during a standardized activity rather than pain at rest. This makes the measurement relevant to the study’s stated interest in movement-related pain and function. The registry lists additional measures addressing resting pain, fatigue, fibromyalgia impact, and pain interference and intensity, reflecting a broader set of outcomes than the primary endpoint alone.

At the same time, the registry record illustrates why design descriptions and hypotheses must be separated from results. It reports the intended analysis features, including mean change, adjusted confidence intervals, site correction, and post hoc comparisons, but does not report the numerical primary outcome estimates or their uncertainty. The design can explain what was compared; without results, it cannot establish the direction or size of any difference.

The record also lists multiple outcomes and analyses, making the prespecification of comparisons, multiplicity handling, and missing-data methods relevant to interpretation. Those details are not reported in the registry record. The statistical importance of the trial therefore lies in the structure of its question and in the limits of what can be concluded from the available record—not in an unreported treatment effect.

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 important trial-specific limitation for interpretation is that numerical primary endpoint results are not reported in the registry record. The record gives the scale, assessment schedule, planned mean changes, adjusted confidence intervals, and description of post hoc comparisons, but not the group estimates, intervals, or p-values. This prevents assessment of effect size, direction, and precision.

The timing of treatment also limits what can be inferred from the later assessment. The first four weeks form the randomized comparison, while all groups received active TENS during the final four weeks. The registry describes the eight-week measure as change from baseline, but does not report numerical results or describe a concurrent group that remained without active TENS at that time.

Further details needed to assess the analysis are not reported in the registry record. These include the implementation of randomization and masking, the exact statistical model, the handling of missing endpoint data, and whether or how multiplicity was addressed. The record states that the primary analysis was intention-to-treat and corrected for site differences between Iowa and Vanderbilt, but does not provide enough detail to evaluate those procedures.

The registry lists serious and other adverse-event counts but does not provide the fuller event definitions, event-level context, or comparative safety analyses needed for causal interpretation. The record also does not report the trial’s sample-size justification. These omissions do not prove that the relevant analyses or procedures were absent; they limit what can be assessed from the registry record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Fibromyalgia Activity Study With Transcutaneous Electrical Nerve Stimulation (FAST) — NCT01888640.
• Registry record last updated 2019-10-31; status last verified 2019-10.
• Results first posted 2019-10-31.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

18. Record Summary

The registry record identifies FAST as a completed randomized, double-masked, parallel study of TENS for fibromyalgia, with enrollment of 301. It lists movement-related pain during the six-minute walk test as the primary endpoint and describes assessments at baseline, four weeks, and eight weeks. The first four weeks compared active TENS, placebo TENS, and no TENS with standard care; all groups received active TENS during the final four weeks.

The record describes mean change from baseline, adjusted 95% confidence intervals, an intention-to-treat analysis corrected for site differences, and post hoc group comparisons. It lists secondary outcomes and adverse-event counts. However, numerical primary endpoint results, missing-data methods, multiplicity procedures, and the sample-size justification are not reported in the registry record. The trial design and planned measures can be described, but the available record does not establish the size or precision of any primary outcome difference.