Efficacy of the Quell Wearable Device for Fibromyalgia: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Efficacy of the Quell Wearable Device for Fibromyalgia (NCT03714425), a randomized na study. The primary outcome is Patients' Global Impression of Change.

2. Clinical Question

The registry record describes hypotheses that the high-frequency group would report reduced pain and show greater improvement in sleep, mood, and activity, and that more frequent device use would be associated with greater pain reduction. Those are the investigators’ stated expectations, not findings established by the posted results. The posted primary outcome is a global rating of perceived change, while the listed secondary measures cover pain, fibromyalgia impact, catastrophizing, disability, anxiety and depression, and helpfulness. The record does not report a result for every listed secondary outcome.

3. Trial Design

The record describes a randomized, double-masked, parallel-group study of the Quell device in fibromyalgia. Participants were assigned to use either a high-frequency or a low-frequency device. The registry lists an enrollment of 119 and marks the study as completed. The sponsor is Brigham and Women's Hospital. The recorded study start is 2019-02-01 and the primary completion date is 2020-12-01.

The comparison is between two device-use groups. It can therefore describe the contrast between assignment to high and low frequency as recorded, but it does not establish how either group compares with no device or with usual care. The registry record does not report the allocation ratio, the randomization procedure, how masking was implemented, or whether participants, investigators, or outcome assessors were all masked. It also does not report participant flow, adherence, actual device-use frequency, or treatment discontinuations.

The primary outcome was the Patients’ Global Impression of Change score at 3 months. The listed secondary measures include the Brief Pain Inventory, Revised Fibromyalgia Impact Questionnaire, Pain Catastrophizing Scale, Pain Disability Index, Hospital Anxiety and Depression Scale, and Helpfulness Rating. Numerical secondary results are not posted for every listed measure. The record gives baseline and 3-month timeframes for the secondary measures with posted values, but does not specify whether those values represent change from baseline or measurements at the stated visits.

The phase is recorded as NA. No sample-size justification, detailed protocol, prespecified analysis plan, or explanation of the enrollment target is reported in the registry record. The enrollment figure should not be taken as proof that every enrolled participant contributed data to every outcome. The analysis populations and the number of observations available for each endpoint are not described beyond the arm-level counts reported with the posted results.

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

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 Patients' Global Impression of Change, measured over 3 months.

The primary outcome is the Patients’ Global Impression of Change (PGIC), reported as a mean score at 3 months. The registry describes it as a 7-point scale in which respondents rate their overall change from very much improved to very much worse. A score of 4 represents no change, and lower values indicate a better outcome. This makes the endpoint a patient-reported global assessment: it captures a participant’s overall belief about treatment efficacy rather than a single pain symptom or a laboratory measure.

A global impression can be useful because it brings a participant’s overall experience into one response. It does not, by itself, show which aspects of health shaped that response, nor does it replace more specific measures of pain, function, sleep, mood, or activity. The registry’s listed secondary outcomes address some of those distinct domains.

The posted primary results give a mean and a 95% confidence interval for each arm. The high-frequency group mean was 3.58, with a 95% confidence interval from 3.09 to 4.07. The low-frequency group mean was 3.24, with a 95% confidence interval from 2.74 to 3.75. Because lower scores represent a better outcome, the descriptive mean is numerically lower in the low-frequency group. These arm-level summaries do not establish the size or statistical uncertainty of a between-group effect. A primary between-group estimate and its inferential test are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous and is summarized with a mean for each arm. A mean gives a compact description of the scores in a group, but it does not show the full distribution of individual responses. The registry gives a 95% confidence interval alongside each primary mean. In general, a confidence interval expresses the uncertainty associated with an estimate under the assumptions of the analysis. It is not a range containing 95% of individual participants’ scores, and an arm-level interval is not itself an interval for the difference between arms.

What does the primary result quantify?

The posted primary values are separate arm means: 3.58 for the high-frequency group and 3.24 for the low-frequency group. The accompanying intervals, 3.09 to 4.07 and 2.74 to 3.75, respectively, describe precision around those means. The registry does not give a contrast between the means or an inferential test for that contrast. A reader cannot use the arm-level confidence intervals as a substitute for a reported between-group confidence interval or p-value. Although the outcome direction makes lower scores more favorable descriptively, a comparison of arm means alone does not quantify the uncertainty in a treatment contrast.

How should the secondary comparisons be read?

The secondary comparisons are unadjusted recalculations from the posted group summaries. A mean difference is expressed as the low-frequency group mean minus the high-frequency group mean. A negative estimate therefore indicates a numerically lower score in the low-frequency group. Whether that direction represents a more favorable result depends on the meaning and scoring direction of the measure. The record explicitly describes the direction of the PGIC scale, but does not give equivalent scoring guidance for the secondary outcomes.

A confidence interval for a mean difference describes the uncertainty around that contrast under the calculation’s assumptions. When an interval includes zero, the posted data are compatible with no difference as well as with differences in either direction at the confidence level used. This is not proof that the groups are identical. When an interval does not include zero, that is evidence of a nonzero difference under the unadjusted calculation, but it does not show whether the difference is important to participants or account for testing several outcomes.

A p-value measures how unusual data at least as inconsistent with a specified null hypothesis would be under the test’s assumptions, if the null hypothesis were true. It is not the probability that the null hypothesis is true, and it does not measure the size or practical importance of an effect. The secondary p-values are unadjusted, and the registry record does not report a multiplicity procedure. They should therefore be interpreted with caution, particularly alongside several listed outcomes.

What do the planning illustrations mean?

The sample-size illustrations use the observed effect as a planning reference, not as evidence of the trial’s design or power. Their stated assumptions are a two-sided significance level of 0.05, equal allocation between the arms, and a normal approximation. They show planning for 100%, 75%, and 50% of the observed effect. For example, planning for 75% of the observed Revised Fibromyalgia Impact Questionnaire effect gives 109 participants per arm for 80% power and 146 participants per arm for 90% power. Planning for 50% of the observed Brief Pain Inventory effect gives 1,683 participants per arm for 80% power and 2,253 participants per arm for 90% power.

These are hypothetical planning illustrations based on observed estimates. They are not the trial’s reported target, a justification for the recorded enrollment, or observed power. Planning calculations that use an observed effect can be sensitive to how large that effect happened to be in the study. The registry does not report the assumptions used to plan the trial, so the illustrations cannot be treated as a reconstruction of the investigators’ original design.

What cannot be assessed from the posted summaries?

The registry does not report the statistical model used for the primary endpoint, covariate adjustment, missing-data methods, or analysis population. The secondary summaries include means and standard deviations, but no individual participant data or distribution plots are described in the record. In general, variability matters because a mean difference is estimated less precisely when observations vary more, all else equal. The posted summaries allow unadjusted calculations but do not permit evaluation of model diagnostics, the effect of outliers, or the impact of departures from analytical assumptions.

The record also does not report whether analyses were prespecified, whether interim analyses occurred, or whether outcome assessments were changed. Those details are not reported in the registry record, so they cannot be inferred from the posted numerical results.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists six secondary outcomes, but numerical results are posted for only three. It reports one primary outcome measure. The record does not state whether the primary endpoint was designated as the sole confirmatory test, whether secondary outcomes were organized into a testing hierarchy, or whether a correction for multiple comparisons was planned or applied. The available secondary p-values are unadjusted. When multiple outcomes are examined, the chance of at least one apparently notable result can increase; in general, adjustment or a prespecified testing strategy can help control that issue. Without a reported strategy, the secondary p-values should not be read as if each were the only analysis conducted.

Missing-data procedures are not reported in the registry record. The arm-level counts attached to the results do not explain whether all participants assigned to each arm contributed observations at the relevant visit, how incomplete questionnaires were treated, or whether any imputation was used. Participant flow, withdrawals, and reasons for missing observations are also not reported. If missingness is related to outcomes or differs between groups, the analyzed results may not represent all randomized participants; the registry record does not provide enough information to assess that possibility.

The analysis population is not described. The registry does not state whether the analyses followed randomized assignment, included only participants who completed treatment, or used another population definition. It also does not report whether baseline scores or other variables were included in an adjusted analysis. These are important details for understanding how a randomized comparison was analyzed and how broadly its results can be interpreted. No analysis plan, interim analysis information, or sample-size justification is reported in the registry record. These absences do not prove that such procedures were not used; they mean that their use cannot be established from the registry entry.

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 0% reporting threshold.

The registry reports zero serious adverse events and zero other adverse events in the high-frequency group, with 62 at risk for each category. It reports zero serious adverse events and zero other adverse events in the low-frequency group, with 57 at risk for each category. The posted death count is zero in each group. No serious adverse-event terms are listed.

These figures describe the events recorded in the registry. A zero count means no event of that category was recorded for the stated group in the posted results; it does not establish that no symptoms or other safety concerns occurred, or that the devices have no risks. The registry record does not provide event definitions, collection procedures, observation time for safety, or a detailed account of non-serious events. It also does not report a statistical comparison of safety between the groups. The counts should therefore be read as a limited description of recorded events, not as a comprehensive assessment of safety or as evidence that the groups are equivalent.

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

The posted primary data describe average PGIC scores at 3 months in the two assigned device-frequency groups. Since lower PGIC values indicate a better outcome, the low-frequency arm’s mean is descriptively lower than the high-frequency arm’s mean. The registry does not report a primary between-group estimate or test, so the strength and precision of that contrast cannot be quantified from the primary results. The arm-specific confidence intervals do not fill that gap.

The secondary summaries show unadjusted differences for several measures, with differing degrees of uncertainty. They do not establish that a difference is clinically meaningful, because the registry does not report thresholds for meaningful change on those scales. They also do not establish that the observed differences were caused by device frequency. The absence of a reported primary comparison, analysis-population details, and missing-data methods limits causal interpretation of the numerical summaries.

The findings do not compare either device frequency with no device or usual care. They should not be generalized beyond the study population and conditions without evidence about the participants, setting, adherence, and longer-term outcomes. The record gives a primary time point of 3 months and does not provide longer-term results in the posted outcomes. It also does not report enough detail to assess whether device use matched assignment or whether adherence differed between groups.

The results therefore support a narrow reading: the registry records group-level scores and selected secondary summaries for a randomized comparison of high- and low-frequency Quell use. They do not provide a reported inferential result for the primary contrast, a complete account of all listed secondary outcomes, or the information needed to settle questions about missing data and analysis populations. The numerical pattern is descriptive and should not be treated as a general claim about efficacy.

13. Why This Trial Matters Statistically

This trial is statistically informative in part because it illustrates the distinction between arm-level summaries and a direct comparison. The primary endpoint includes a mean and confidence interval for each group, but the registry does not report the contrast between those groups. A reader needs that contrast, with its uncertainty, to assess how precisely the primary data distinguish the assigned strategies. Separate confidence intervals around group means do not supply the same information.

The record also illustrates why secondary outcome results need context. Several measures are listed, only some have posted numerical results, and the available p-values are unadjusted recalculations. A result that appears noteworthy in one outcome must be considered alongside the other outcomes, the primary endpoint, the direction and meaning of each scale, and the analysis plan. Here, the testing strategy and clinical interpretation thresholds are not reported, so the role of an individual secondary result remains uncertain.

Finally, the sample-size illustrations show how planning estimates depend on the effect size chosen for planning. They are explicitly based on observed effects and stated assumptions, not on the trial’s documented design. Treating those illustrations as observed power or as the original sample-size rationale would confuse post hoc planning scenarios with prospective design decisions. The registry does not report the original sample-size justification.

Together, these features make the record a useful example of how reporting detail affects statistical interpretation. The randomized, masked, parallel design provides important context, but design labels alone cannot answer questions about outcome analysis, missingness, multiplicity, or precision of the primary contrast. Transparent reporting of those elements is necessary to judge the strength and scope of the numerical evidence.

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 record constrain interpretation. Most notably, the primary outcome is reported as separate arm means with arm-level confidence intervals, but no primary between-group estimate or inferential test is reported. The primary result is therefore descriptive rather than a complete statistical comparison. The reported time point is 3 months, and longer-term outcome results are not reported in the registry record.

The secondary outcome reporting is incomplete. Six secondary outcomes are listed, while numerical arm results and unadjusted comparisons are available for only three. The record does not provide sponsor-reported analyses for those posted comparisons, and the recalculations do not account for multiplicity. The scoring direction and interpretation thresholds for the secondary scales are not described in the record, limiting conclusions about the meaning of their numerical differences.

Other important details are not reported in the registry record: participant flow, analysis populations, missing-data handling, baseline adjustment, adherence, and the statistical analysis plan. The arm-level counts do not establish how many observations were available at each measurement or whether all randomized participants were included in analyses. Although the record describes a randomized, double-masked design, details about randomization and masking procedures are absent.

The safety results are also limited to posted counts, without event definitions or collection details. Zero recorded events do not establish absence of all safety concerns. Finally, the study compares two device frequencies, not device use with no device, and the registry does not provide the details needed to assess how well results generalize beyond this study. These limitations concern what can be concluded from the registry record; they do not establish that unreported procedures or analyses were not performed.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Efficacy of the Quell Wearable Device for Fibromyalgia — NCT03714425.
• Registry record last updated 2022-08-15; status last verified 2022-07.
• Results first posted 2022-06-21.
• 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 describes a completed randomized, double-masked, parallel-group study of high- versus low-frequency Quell devices for fibromyalgia, sponsored by Brigham and Women's Hospital. It lists an enrollment of 119 and a primary endpoint of Patients’ Global Impression of Change at 3 months. Lower PGIC scores represent a better outcome. The posted arm means are 3.58 for high frequency and 3.24 for low frequency, each with a 95% confidence interval. A primary between-group comparison is not reported.

Numerical secondary results and unadjusted recalculations are available for three measures, while other listed secondary outcomes have no posted numerical results in the registry record. The record does not report the analysis population, missing-data methods, multiplicity strategy, or sample-size justification. Recorded serious and other adverse-event counts, and deaths, are zero in both groups. Those counts are limited to the events documented in the registry.