Simplified Negative Pressure Wound Therapy: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Simplified Negative Pressure Wound Therapy (NCT01339429), a na phase 1 study. The primary outcome is Maintenance of Negative Pressure.

2. Clinical Question

3. Trial Design

NCT01339429, titled “Simplified Negative Pressure Wound Therapy,” was a phase 1, completed study sponsored by Brigham and Women's Hospital. The registry records enrollment of 41 participants and describes a single-group design. Allocation is listed as not applicable, and masking is listed as none. There is no randomized control group in the registry description.

Participants selected from the hospital ward and meeting the eligibility criteria received the simplified negative pressure wound therapy device. The study objective was to implement this device in a low resource setting. The stated aims were to measure its mechanical properties and assess adverse events. The study description also states a hypothesis that the device is at least equivalent to commercially available devices. That stated hypothesis is not itself evidence of equivalence: the record does not describe a concurrent comparator, an equivalence margin, or a statistical comparison that would test equivalence.

The primary outcome was maintenance of negative pressure, measured daily for 3 days and expressed in hours. Although 85 dressings were applied, the primary-outcome analysis included 71 dressings. The registry reports exclusions associated with a change in patient condition unrelated to the device and with drainage-tube occlusion. The number of dressings analyzed is not the same as the participant enrollment; the record does not explain how the analyzed dressings were distributed across participants.

The registry lists a secondary outcome concerning participants with serious adverse events. It does not report a detailed statistical analysis plan, a sample-size justification, or interim analyses. The study's completed status does not fill in those missing details. The record also does not provide a numerical primary-outcome estimate, its variability, or a comparative estimate.

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.

Before assignment: 47 patients consented. 6 did not meet inclusion criteria. 1 voluntarily withdrew. 4 not enrolled due to clinical changes.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: 85 dressings were applied. 5 applications excluded due to a change in patient condition, unrelated to sNPWT. 9 dressings excluded due to occlusion of the drainage tube. 71 dressings were analyzed in total.

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 Maintenance of Negative Pressure, measured over 3 days.

The primary endpoint, “Maintenance of Negative Pressure,” concerns the duration for which the device delivered pressure within 75% of the starting negative pressure amount. The registry says pressure was measured daily for 3 days and identifies the unit as hours. In practical terms, the endpoint is intended to describe whether pressure delivery remained sufficiently close to the starting level over the observation period. It is a device-performance measure, rather than a direct measure of wound healing or patient benefit.

The registry identifies the outcome as a continuous measure summarized by a mean and standard deviation. In general, a mean describes the central value of a set of measurements, while a standard deviation describes how dispersed the measurements are around that mean. Reporting both can help readers understand typical performance and variability. However, neither the mean nor the standard deviation is reported in the registry record, and no confidence interval is given. The numeric endpoint value and its precision therefore cannot be assessed from the posted information.

The analysis population is stated in terms of dressing applications. The registry reports that 85 dressings were applied and 71 were analyzed, after exclusions for specified reasons. These counts indicate the scope of the endpoint data, but they do not reveal the distribution of measured hours or whether multiple dressings from the same participant were statistically handled as related observations. The registry record does not report that analytic detail.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes the primary outcome as a continuous measure, with a mean and standard deviation as the intended summary. In general, a continuous outcome can take values across a measurement scale rather than being limited to categories. Here, the scale is hours of negative pressure maintenance. A mean can give a compact description of the measured durations, while a standard deviation conveys how much the observed durations vary. These summaries are most informative when the number of observations and the analyzed population are also clear. The record gives the number of analyzed dressings, but does not give the mean or standard deviation.

What the endpoint definition contributes

The endpoint is defined by a threshold relative to the starting pressure: delivery within 75% of the starting amount. The pressure was measured daily for 3 days, and the endpoint is expressed in hours. In general, a defined threshold makes a performance criterion more explicit than an unqualified description such as “maintained pressure.” It does not, by itself, show how the measured values were converted into duration, how measurements between daily assessments were treated, or how missing measurements were handled. Those details are not reported in the registry record.

How to read the study structure

This is a single-group study, with no masking and no allocation to a control group. In general, a single-group design can describe measurements observed after an intervention, but it cannot isolate the intervention's effect from other explanations as directly as a controlled comparison can. The registry's stated equivalence hypothesis concerns commercially available devices, yet the record does not describe a concurrent comparison with such devices. No equivalence margin or comparative statistical procedure is reported.

The unit counted for the primary endpoint is the dressing application, while enrollment is recorded as 41 participants. The registry says 85 dressings were applied and 71 were analyzed. In general, when several observations may come from the same participant, those observations can be statistically related rather than independent. Treating related observations as though they were independent can make uncertainty appear smaller than it is. The record does not say how many dressings came from each participant or what method, if any, accounted for within-participant dependence. This is a question about analytic detail, not proof that the analysis was incorrect.

Precision and uncertainty

A confidence interval is a general way to express uncertainty around an estimate: it gives a range of values compatible with the data and the specified statistical method. Its width depends on factors such as the amount of information and variability. The registry does not report a confidence interval for the primary endpoint, and it does not provide the underlying mean or standard deviation. Consequently, the precision of the endpoint estimate cannot be evaluated from the record. A point estimate without uncertainty would also be incomplete for judging how stable an observed result might be.

Over-dispersion is a general concern when data vary more than a chosen statistical model expects. It can arise, for example, when measurements differ substantially across participants or when observations are clustered. Recognizing such variation may affect the choice of model and the uncertainty estimate. The registry does not report a model for the primary endpoint, a diagnostic assessment, or information that would establish whether over-dispersion was considered. No claim about its presence or absence can be made from the posted record.

Planning calculations and observed evidence

Sample-size calculations are planning illustrations: they describe how many observations might be needed under specified assumptions to target a chosen level of statistical power for a particular effect. They are not observed results and do not show that a completed study had a given probability of finding an effect. The described planning assumptions refer to a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect defined as a fraction of the observed effect. However, this trial is single-group, and the registry does not provide a numerical observed effect or the resulting planning figures. The record does not report the trial's own sample-size justification. Any planning illustration based on an observed effect should not be mistaken for a prespecified design rationale or for a finding from this study.

The registry reports 0 analyses. This means the record does not list a statistical analysis for the outcomes. It does not provide a hypothesis test, a p-value, an adjusted estimate, or a model specification for the primary outcome. In general, a p-value measures how compatible data are with a specified null model under stated assumptions; it does not express the probability that a treatment works. No such inference can be evaluated for the primary endpoint from the record because no analysis result is reported.

For safety, the registry gives event counts and numbers at risk. These are descriptive summaries. General methods for comparing adverse-event rates would require a clearly defined comparison and sufficient information about event definitions and follow-up; no comparative safety analysis is reported. The counts should therefore be read within the limits of the single group and the brief registry detail, not as a formal comparative test.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Simplified Negative Pressure Wound Therapy")
n   <- c(37)
m   <- c(22.2)
sp  <- c(27)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Simplified Negative Pressure Wound Therapy  37  22.200  27.000  13.198  31.202

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 2 outcome measures and names maintenance of negative pressure as the primary outcome, with serious adverse events as a secondary outcome. It reports 0 analyses. The record does not describe a statistical analysis plan, specify which outcome analyses were prespecified, or state whether any adjustment for multiple testing was intended.

Multiplicity arises in general when several outcomes, groups, time points, or statistical tests are examined. Testing many questions can increase the chance that at least one appears noteworthy by chance if the analyses are interpreted without accounting for that multiplicity. Whether an adjustment is needed depends on the scientific questions and the analysis plan. Since the registry record does not report outcome-level analyses or an adjustment strategy, it is not possible to assess how multiplicity was handled. This absence does not establish that an adjustment was either required or omitted in a separate analysis.

The record says that 85 dressings were applied and 71 were analyzed. It attributes the exclusions to a change in patient condition unrelated to the device and to drainage-tube occlusion. It does not report an imputation method, a sensitivity analysis, or an analysis of all applied dressings. In general, missing-data methods depend on why observations are absent and on assumptions about the relationship between missingness and the unobserved measurement. The registry does not provide enough information to assess those assumptions.

Enrollment of 41 participants and analysis of 71 dressings describe different units. The registry does not specify the analysis population in terms of participants beyond the reported dressing count, nor does it describe how repeated observations within participants were treated. These details, along with the absence of a numerical endpoint estimate and analytic plan, limit assessment of the statistical handling of the outcome.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry records 0 serious adverse events among 41 participants at risk in the simplified negative pressure wound therapy group. It also records 1 other adverse event among 41 participants at risk. These are counts from the single study group, not a comparison between devices or treatments. The registry does not list serious adverse-event terms, and it does not provide detail about the other event. A death count is not reported in the registry record.

In general, an observed count is a description of what was recorded during the study, not proof that an event cannot occur. A zero count can coexist with uncertainty about the underlying event risk, particularly when the record does not provide a confidence interval, detailed follow-up information, or a comparison group. Conversely, the single other adverse event cannot by itself establish a causal relationship with the device. The registry's brief summary does not state whether that event was considered related.

The counts should be interpreted alongside the study's size and single-group design, without converting them into a comparative claim. The record does not report a formal safety analysis, time-to-event assessment, or detailed definitions for the events. These omissions limit what can be inferred about safety from the posted figures.

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

The posted record shows that the study evaluated a simplified negative pressure wound therapy device in a single group and defined maintenance of negative pressure as delivery within 75% of the starting amount. Pressure was measured daily for 3 days. The primary-outcome population is described as 71 analyzed dressings from 85 applications, with exclusions attributed to a change in patient condition unrelated to the device and to drainage-tube occlusion. The record also reports 0 serious adverse events and 1 other adverse event among 41 participants at risk.

Those details describe the study's structure and recorded observations, but the central numerical primary-outcome result is not reported in the registry record. There is no mean maintenance duration, standard deviation, confidence interval, or comparative estimate in the posted information. Therefore, readers cannot assess the observed level or precision of the device-performance measure from this record.

The study description states an intention to assess equivalence to commercially available devices, but does not describe a concurrent comparator, an equivalence margin, or an analysis testing equivalence. A stated objective or hypothesis is not a demonstrated result. The posted information also does not establish comparative safety, since the adverse-event counts are from one group.

In general, a study's findings are interpreted in light of its design, outcomes, analysis, and uncertainty. Here, the single-group structure, the difference between participant and dressing counts, the reported exclusions, and the lack of numerical endpoint results constrain interpretation. The results do not establish that the device is equivalent to other devices, nor do the available safety counts prove the absence of risk. Equally, the missing numerical endpoint estimate does not show that performance was poor. The defensible reading is that the registry describes the evaluation and its outcome definitions but leaves key efficacy and precision information unreported.

14. Why This Trial Matters Statistically

This trial is statistically informative as an example of why outcome definitions, analysis units, and numerical estimates all matter. The registry defines a mechanical-performance endpoint in terms of a pressure threshold and reports the number of dressing applications analyzed. That provides useful context about what was intended to be measured, but without the observed mean and its variability, the degree of performance and its uncertainty cannot be judged.

The distinction between participants and dressings is important. The record reports enrollment of 41 participants and analysis of 71 dressings. In general, multiple measurements from one participant may be correlated. Statistical methods need to reflect the actual structure of the data so that uncertainty is not understated. The registry does not describe how dressings were distributed across participants or how such dependence was handled. That makes the analytic unit a key consideration for interpreting any separate results.

The study also illustrates the distinction between a research hypothesis and a design capable of testing it. The registry states an equivalence hypothesis, while describing a single-group study without a concurrent control. Equivalence is a comparative claim; evaluating it typically depends on an appropriate comparison and a prespecified margin. Those details are not reported in the registry record, so the stated hypothesis cannot be read as an established conclusion.

Finally, the adverse-event counts are useful descriptive information but do not substitute for a comparative safety analysis or detailed event reporting. The record's missing primary estimate, uncertainty measures, and analysis plan show why clear reporting is essential: readers need enough information to distinguish a study objective from an observed finding and to understand how precisely that finding is estimated.

15. 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 direct limitation of the registry record is that it does not report a numerical primary-outcome result. Although the outcome definition, unit, timeframe, and analysis count are given, the mean and standard deviation are absent. No confidence interval or other precision measure is reported. The primary performance finding therefore cannot be evaluated from the posted information.

The design is single-group, with no concurrent comparator, and the registry lists no masking. This structure does not provide a direct comparison with commercially available devices. Although the study description states a hypothesis of at least equivalent performance, the record does not report an equivalence margin or comparative analysis. The study description also does not permit a conclusion that the hypothesis was confirmed.

The primary outcome is described in dressing applications, while enrollment is reported in participants. The record does not report how the 71 analyzed dressings were distributed across participants or how possible within-participant dependence was handled. It reports exclusions among the 85 applications, but does not describe imputation, sensitivity analyses, or analyses that included excluded applications. The reasons are stated, but the effect of those exclusions on the estimate cannot be assessed without the outcome data.

Statistical reporting is limited: the registry reports 0 analyses and does not provide a detailed analysis plan, sample-size justification, interim-analysis information, model specification, or multiplicity strategy. It does not provide detailed descriptions of adverse events or a death count. These are limitations of what the registry record reports; they do not establish what may or may not have been conducted outside the posted record.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Simplified Negative Pressure Wound Therapy — NCT01339429.
• Registry record last updated 2015-05-20; status last verified 2015-05.
• Results first posted 2015-05-20.
• 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.

19. Record Summary

NCT01339429 was a completed phase 1, single-group study of a simplified negative pressure wound therapy device, with enrollment of 41 participants. The study aimed to implement the device in a low resource setting and assess mechanical properties and adverse events. Its primary outcome was maintenance of negative pressure, defined as delivery within 75% of the starting amount and measured daily for 3 days.

The registry reports 85 dressing applications and 71 analyzed dressings, with exclusions attributed to a change in patient condition unrelated to the device and to drainage-tube occlusion. The numerical primary-outcome result is not reported in the registry record. The safety record lists 0 serious adverse events and 1 other adverse event among 41 participants at risk. No concurrent comparator or numerical comparative analysis is reported, so the stated equivalence hypothesis is not established by the posted information.