This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Electrical Stimulation of the Muscle Pumps of the Leg (NCT02532556), a non-randomized na study. The primary outcome is Venous Haemodynamic Measurements (Volume Flow Rate).
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT02532556 |
| Phase | NA |
| Condition | Haemodynamic Physiology |
| Allocation | Non-Randomized |
| Design model | Single Group |
| Masking | Triple |
| Enrollment | 12 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Imperial College London |
| Results posted | Yes |
2. Clinical Question
Population
The record concerns participants whose leg muscles were stimulated. It lists an enrollment of 12 and identifies haemodynamic physiology as the condition area. Further eligibility details and participant characteristics are not reported in the registry record.
Intervention
The intervention was electrical muscle stimulation using a Digitimer device. The study description says the investigators aimed to examine a matrix of electrical parameters and measure the response with vascular ultrasound. The listed arm descriptions give different orders in which muscles were stimulated, including muscles of the thigh, lower leg and calf. Details of the electrical settings are not reported in the registry record.
Comparator
The study is described as single-group and non-randomized. It does not provide a separate control group for a like-for-like comparison. The primary measurement compares baseline with a measurement after stimulation; this is a within-participant time comparison, not evidence of a randomized treatment contrast.
Primary question
The primary outcome is venous flow rate measured by ultrasound in the right femoral vein. The registry describes measurement at baseline and after 10-mins stimulation, with 2-mins to take measurements. The question is whether the recorded flow rate differs across those measurement occasions in the stimulated-muscle population. The posted results do not give the values needed to describe the size, direction or precision of any change.
3. Trial Design
The study is registered as completed, with a start date of 2015-05 and primary completion in 2015-08. It is categorized as phase NA. Imperial College London is listed as the sponsor. Enrollment is recorded as 12.
The registry characterizes the design as single-group and the allocation as non-randomized. It also records triple masking, but does not describe which groups of people were masked or how masking was implemented. The listed intervention is electrical stimulation using a Digitimer device. Arm descriptions set out different orders for stimulating named muscles. They do not establish that participants were randomly assigned to those orders, nor do they describe a concurrent control condition. The record specifically warns that the listed arms are not a like-for-like control comparison.
The primary outcome is a measurement of venous haemodynamics, expressed as volume flow rate in ml/min and measured by ultrasound in the right femoral vein. The recorded timeframe compares baseline with measurement after 10-mins stimulation, allowing 2-mins to take measurements. The outcome description identifies the population as muscle stimulated. Pain grading on stimulation is listed as a secondary outcome.
The registry lists three outcome measures and two analyses, but the names and details of all measures and analyses are not reported in the registry record. The protocol, full electrical stimulation settings, timing of each muscle sequence, participant flow and analysis population are also not reported in the registry record. These omissions limit reconstruction of the study procedures and statistical analysis.
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
| Stage | Electrical Muscle Stimulation Participants |
|---|---|
| STARTED | 12 |
| COMPLETED | 12 |
| NOT COMPLETED | 0 |
Analysis population for the primary outcome, as defined in the registry: Muscle stimulated
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.
| Characteristic | Unit | Electrical Muscle Stimulation Participants |
|---|---|---|
| Participants analysed | 12 | |
| Age, Continuous | years | 23.1 (SD 3) |
| Sex: Female, Male: Female | Participants | 7 |
| Sex: Female, Male: Male | Participants | 5 |
| Region of Enrollment: United Kingdom | participants | 12 |
| Body mass index | kg/m^2 | 23.1 (SD 3) |
6. Primary Endpoint
The registry lists the primary outcome as Venous Haemodynamic Measurements (Volume Flow Rate), measured over Baseline compared to that after 10-mins stimulation (2-mins to take measurements).
| Element | Registry entry |
|---|---|
| Result type | Median |
| Measure of spread | Standard Deviation |
| Unit | ml/min |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is venous volume flow rate, measured in ml/min by ultrasound in the right femoral vein. The record describes a baseline measurement and a further measurement after 10-mins stimulation, with 2-mins to take measurements. The outcome is intended to capture a haemodynamic response in the stimulated-muscle population.
As a general statistical and physiological concept, flow measurements can describe blood movement through a vessel and may be useful when a study is concerned with circulation-related responses to muscle stimulation. A paired baseline and post-stimulation design can describe how a measurement changes within the observed study setting. It does not, by itself, separate a stimulation-related change from changes that could occur over time or through measurement variability. A comparison group and information about measurement procedures can help with that interpretation, but the record describes a single-group study.
The registry identifies the summary parameter as the median and the measure of dispersion as the standard deviation. These are the recorded summary choices, but numerical values for the endpoint are not reported in the registry record. Consequently, the magnitude and direction of the recorded flow response, and its precision, cannot be assessed from the posted information.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The record establishes the study question and several features of its design, but it does not report numerical results for the primary endpoint. There is no posted baseline flow rate, post-stimulation flow rate, change estimate, confidence interval or test result in the registry record. It is therefore not possible to state whether flow was higher or lower after stimulation, how large any observed change was, or how uncertain an estimate might be.
The primary endpoint is described as a median with standard deviation. The record does not provide the values for either summary. A median can describe the middle of a distribution, while a standard deviation describes spread around the mean; as a general statistical point, the two summaries characterize different aspects of a distribution. Their interpretation cannot be checked without the underlying result values and further analysis details. The registry does not report whether the analysis used individual paired measurements, a model, or another method.
The design matters when interpreting any before-and-after findings. A within-participant comparison can show that measurements differed between the recorded occasions, but the non-randomized, single-group design does not provide a concurrent randomized comparison. Changes cannot therefore be attributed to stimulation alone on the basis of the design description. Measurement conditions, time effects and other influences could contribute, but their role cannot be assessed from the record.
The arm descriptions list different orders of muscle stimulation. The record does not report an analysis comparing those orders, nor does it describe how the listed sequences were assigned or whether every participant experienced each sequence. The study summary says that a matrix of electrical parameters was of interest, but the parameter settings and their results are not reported in the registry record. It would be inappropriate to infer which order or setting produced a larger response.
Pain grading on stimulation is named as a secondary outcome, but its results are not reported in the registry record. The registry also lists three outcome measures and two analyses without giving full descriptions of each. No conclusions about the direction, size or statistical significance of outcomes can be drawn from those counts alone.
Overall, the posted information describes a completed investigation of electrical stimulation and ultrasound-measured venous flow. It does not provide the outcome estimates needed to characterize what was observed. Any numerical interpretation must await results in the registry record or another identified source; no such source is specified in the record.
9. Statistical Methods Explained
What does a before-and-after measurement estimate?
In general, a before-and-after design records an outcome at an initial time and again after an intervention or exposure. When measurements come from the same participant, the two values are related. An analysis that respects this pairing focuses on within-participant changes rather than treating each measurement occasion as if it came from unrelated people. Such a comparison can describe change during the study procedure, but without an appropriate comparison condition it does not isolate the cause of that change.
For this study, the registry says that ultrasound measurements of right femoral-vein flow were taken at baseline and after 10-mins stimulation, with 2-mins to take measurements. It does not state whether each participant contributed both measurements, how missing measurements were handled, or which statistical procedure was used. The analysis method is therefore not identifiable from the recorded description.
What do median and standard deviation convey?
The primary outcome description names the median as the parameter and standard deviation as the dispersion measure. In general, the median marks the central value after observations are ordered; it is less affected by extreme values than the mean. The standard deviation is commonly used to describe the spread of observations around their mean. Because they describe different features of a distribution, a median and standard deviation do not by themselves show the full shape of the data. A distribution plot, additional quantiles or participant-level data can add context, but these are not described in the registry record.
A summary of each measurement occasion would not necessarily answer the same question as a summary of paired changes. For paired measurements, the distribution of individual changes can differ from the separate distributions at baseline and after stimulation. The registry record does not report whether it summarizes the paired differences, nor does it provide estimates or uncertainty intervals. The reader should not infer these from the choice of summary parameter alone.
What does a confidence interval mean?
As a general concept, a confidence interval gives a range of estimates compatible with a statistical procedure applied to the observed data. Its width reflects both the variability in the data and the amount of information available under the model. A narrow interval indicates greater precision for the quantity being estimated; a wide interval indicates less precision. A confidence interval is not a guarantee that the true effect lies within that particular interval, and its interpretation depends on the analysis assumptions.
No confidence interval for the primary outcome is reported in the registry record. Nor does the record state a statistical model, a standard error, a test statistic or a significance threshold for the outcome analysis. Without these details and the result values, neither statistical precision nor compatibility with a null value can be assessed.
Why can over-dispersion matter?
In general, over-dispersion occurs when observed variability is greater than a statistical model expects. A model that assumes less variation than is actually present can understate uncertainty and make results appear more precise than they are. Models that accommodate over-dispersion, or robust approaches, may be appropriate for some outcome types. This study's primary endpoint is a continuous flow measurement, and the record does not report that over-dispersion was assessed or that any particular model was used. This general issue should not be mistaken for evidence that over-dispersion occurred in this study.
What can the design say about causation?
In general, random assignment can help balance measured and unmeasured influences between comparison groups, while a concurrent control can help distinguish an intervention effect from changes that might otherwise occur. This record identifies the allocation as non-randomized and the model as single-group; it also notes that the arms are not a like-for-like control comparison. Baseline-to-post-stimulation measurements can still describe the observed temporal pattern, but other explanations for a difference remain possible. The record does not describe adjustment for confounding, a causal model or sensitivity analyses.
What is known about the analysis plan?
The registry lists two analyses, but their methods and outcomes are not described in the record. The statistical analysis plan, choice of hypothesis tests, handling of repeated measurements, confidence-interval method and assumptions are not reported in the registry record. It is also not reported whether there were interim analyses or a sample-size justification. The enrollment figure is a record of enrollment, not an explanation of how the study size was selected. Any planning illustration based on observed effects should be understood as an illustration, not as observed power or proof that the original design had a particular power.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists three outcome measures and two analyses. It names venous flow rate as the primary outcome and pain grading on stimulation as a secondary outcome, but does not identify every outcome measure or provide the full analysis descriptions. It is therefore not possible to determine how many outcome comparisons were actually tested, whether multiple muscle orders or electrical settings were analyzed separately, or whether any multiplicity adjustment was used. The statistical plan for handling multiple outcomes or comparisons is not reported in the registry record.
As a general statistical issue, repeated testing across outcomes, settings or subgroups can increase the chance of finding an apparently notable result by chance. Adjustment procedures can address some forms of multiplicity, but their choice depends on the questions and analysis plan. No particular adjustment can be attributed to this study from the registry description.
Missing-data methods are not reported in the registry record. The record does not say whether all enrolled participants completed the measurements, whether any values were missing, or how missing observations were handled. It also does not define an analysis population, such as all enrolled participants or those with usable measurements. The enrollment entry alone does not resolve these questions.
The registry does not describe whether the primary analysis used all recorded observations, a complete-case subset or another population. These omissions limit assessment of possible bias from missing data and the consistency between the planned and reported analyses. No conclusion about missingness or analysis-population selection should be inferred where the record is silent.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Electrical Muscle Stimulation Participants | 0 | 12 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Electrical Muscle Stimulation Participants | 0 of 12 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Electrical Muscle Stimulation Participants | 0 of 12 |
The registry reports serious adverse event information for the Electrical Muscle Stimulation Participants group. It records 12 participants at risk for serious adverse events and 0 affected. For other adverse events, it records 12 at risk and 0 affected. Deaths are recorded as 0, and no top serious-event terms are listed.
These figures describe what is recorded in the registry; they do not establish that no adverse events of any kind occurred, since the record lists zero affected in the serious and other adverse-event fields and does not provide additional event narratives. The period during which participants were monitored, the rules for collecting events, and the completeness of follow-up are not reported in the registry record. The record also does not provide detailed severity, relatedness or event-specific information.
As a general statistical point, an absence of recorded events in a study does not establish that the underlying risk is zero. Safety estimates depend on the number observed, the duration and completeness of surveillance, and the event definitions used. These registry figures should be read as reported counts, not as a comprehensive demonstration of safety or a comparison with another intervention.
12. What the Result Does, and Does Not, Mean
The record describes an investigation of electrical stimulation of leg muscles and ultrasound measurement of venous flow. Its primary question concerns a measurement at baseline compared with a measurement after 10-mins stimulation, with 2-mins to take measurements. The record also identifies pain grading on stimulation as a secondary outcome. These details establish what the investigators set out to measure, not what the measurements showed.
The primary outcome values and their uncertainty are not reported in the registry record. Consequently, the posted information does not establish the direction or size of any difference in flow, the precision of an estimate, or whether an analysis found evidence inconsistent with a null hypothesis. It also does not say which muscle order or electrical setting, if any, had a different observed response. No treatment-effect claim is supported by the information recorded.
Even if numerical before-and-after results were available, interpretation would need to account for the study design. The record labels the study single-group and non-randomized and states that the arms are not a like-for-like control comparison. In general, this design can describe observations over time but cannot on its own distinguish an intervention-related effect from other explanations for a change. The registry does not report adjustment methods that could address these concerns.
Nor does the record establish how broadly any observation would apply. Participant eligibility details and participant characteristics are not reported in the registry record. The recorded enrollment is 12, but enrollment alone does not show whether the study population represents another clinical or research population.
The appropriate conclusion is limited: the registry documents a completed study design and specified haemodynamic measurement, while leaving the numerical results and important analysis details unavailable. It neither demonstrates benefit nor demonstrates lack of effect. It supports no medical recommendation; it provides a basis for identifying what results and methods would be needed for a fuller statistical assessment.
13. Why This Trial Matters Statistically
This study is statistically interesting because it links a physiological measurement to a structured stimulation procedure. The primary endpoint is a quantitative ultrasound measure of right femoral-vein flow, recorded before and after stimulation. The listed muscle orders and the stated interest in a matrix of electrical parameters raise questions about how stimulation sequence and settings relate to measured response.
Those questions make design and analysis particularly important. Different orders of stimulation may be of interest, but the record does not explain their assignment, whether each participant experienced each order, or how order effects were analyzed. The study is identified as single-group and non-randomized, and the record warns that its arms are not a like-for-like control comparison. This makes it important not to interpret sequence descriptions as randomized treatment groups.
The endpoint also illustrates why summaries need to match the research question. Separate baseline and post-stimulation summaries can describe the observations at each occasion, whereas paired changes address within-participant differences. The registry identifies a median and standard deviation but gives no numerical results or analysis method. Without knowing how dependence between measurements was handled, the precision of an estimate cannot be evaluated.
Finally, the record demonstrates the distinction between a well-defined measurement question and an answer to that question. It identifies the outcome, timeframe, intervention and enrollment, yet does not report the primary results, analysis details or missing-data approach. Statistical interpretation requires those elements as well as design information. The available record therefore supports discussion of the study's measurement and design, but not a conclusion about the observed haemodynamic response.
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 details needed to assess this study are not reported in the registry record. The eligibility criteria, participant characteristics, recruitment details and participant flow are unavailable. Enrollment is recorded as 12, but it is not clear from the record how many participants completed each measurement or contributed to each analysis.
The stimulation procedure is described in broad terms. The record does not state the electrical parameters, their levels, how stimulation was delivered, how long each muscle was stimulated, or whether the listed orders were assigned or experienced by each participant. It also does not explain the triple-masking designation or identify who was masked.
The outcome information is incomplete. Although the primary measure and timeframe are identified, numerical flow results and uncertainty estimates are not reported in the registry record. Pain grading is named as a secondary outcome, but its results and measurement details are not reported. The record lists three outcome measures and two analyses without fully describing them.
The analysis plan, handling of repeated measurements, missing-data procedures, analysis population, multiplicity approach and sample-size justification are not reported in the registry record. There is also no description of interim analyses. Without these details, the analysis cannot be independently reconstructed, and the precision or robustness of any unreported result cannot be evaluated.
The single-group, non-randomized design limits causal interpretation, and the registry notes that the arms are not a like-for-like control comparison. The observation period for adverse events and the completeness of safety follow-up are also not reported. These limitations do not establish that the procedures were inadequate; they identify what cannot be determined from the registry record.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Electrical Stimulation of the Muscle Pumps of the Leg — NCT02532556.
- Registry record last updated 2020-11-27; status last verified 2020-11.
- Results first posted 2020-11-27.
- 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.
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18. Record Summary
The record describes a completed, single-group, non-randomized study sponsored by Imperial College London, with enrollment of 12. Its intervention was electrical stimulation of leg muscles using a Digitimer device. Different orders of muscle stimulation are listed, and triple masking is recorded, although masking procedures are not described.
The primary outcome was venous volume flow rate in the right femoral vein, measured by ultrasound at baseline and after 10-mins stimulation, with 2-mins to take measurements. Pain grading on stimulation is listed as a secondary outcome. The registry records 0 serious adverse events, 0 other adverse events and 0 deaths among 12 participants at risk in the respective fields.
Numerical primary-outcome results, full analysis methods, missing-data procedures and complete descriptions of all listed outcomes are not reported in the registry record. The posted information therefore describes the study question and design but does not permit a quantitative interpretation of its haemodynamic findings.