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 Effects of Different Support Surfaces on the Properties Skin After Loading (NCT02930590), a randomized na study. The primary outcome is Transepidermal Water Loss (TEWL) in g/m2/h on Sacrum, at Baseline.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT02930590 |
| Phase | NA |
| Condition | Pressure Ulcers |
| Allocation | Randomized |
| Design model | Crossover |
| Masking | None (open label) |
| Enrollment | 15 |
| Arms in the primary outcome | 3 |
| Lead sponsor | Charite University, Berlin, Germany |
| Results posted | Yes |
2. Clinical Question
Population
The study included 15 female participants between 60 and 80 years of age. Each participant lay on each of the three mattress types in this crossover trial. The registry lists pressure ulcers as the condition of interest, but the posted primary measure is a skin-function measurement rather than a count of pressure ulcers.
Intervention
One surface was an alternating low-pressure mattress with a low-air-loss function. The registry describes this as an alternating low-pressure mattress and identifies the product as IsoAir. The study aim was to measure skin responses after two hours of loading.
Comparator
The other surfaces were a reactive support surface, described as a gel mattress, and a standard mattress made of basic foam. The study therefore exposed each participant to all three types of surface rather than assigning separate groups to remain on just one surface.
Primary question
The registered primary outcome is transepidermal water loss (TEWL) on the sacrum at baseline, measured in g/m2/h. The broader study aim concerned skin responses at the heel and sacrum after two hours on the different surfaces, with the sternum as a control area. However, the primary endpoint named in the record is a baseline measurement; a primary post-loading contrast between surfaces is not reported in the registry record.
3. Trial Design
This was a randomized, unmasked crossover study with a registry enrollment of 15. The primary-outcome description specifies 15 female participants aged 60 to 80 years, each of whom lay on each of the three types of mattress. In a crossover design, participants receive or experience multiple conditions, so measurements from the same person are related. That feature matters when comparing conditions: an analysis should account for the within-person structure rather than treat every measurement as if it came from a different participant. Whether and how that structure was handled in the trial’s analysis is not reported in the registry record.
The three surfaces were an alternating low-pressure mattress with low-air-loss function, a gel mattress identified as a reactive support surface, and a standard basic-foam mattress. The study description states that the intended loading period was two hours. Skin responses were of interest at the heel and sacrum, with the sternum included as a control area. The registry outcome list includes measurements at baseline, after loading, and after off-loading for some skin-temperature outcomes, along with erythema measurements. The primary outcome, however, is sacral TEWL at baseline.
Allocation is recorded as randomized and masking as none. The order of surface exposure, the method used to randomize the order, any washout or recovery period between exposures, and any procedures used to limit carryover are not reported in the registry record. Those details are relevant in crossover research because an earlier exposure could affect measurements during a later condition. The record identifies the study as completed, with start and primary-completion dates of 2016-09 and 2017-03. A phase is listed as not applicable.
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.
First Intervention (2 Hours)
| Stage | Low Pressure, Reactive Support, Than Standard Mattress | Low Pressure, Standard Mattress, Than Reactive Support | Reactive Support, Low Pressure, Than Standard Mattress | Reactive Support, Standard Mattress, Than Low Pressure | Standard Mattress, Low Pressure, Than Reactive Support | Standard Mattress, Reactive Support, Than Low Pressure |
|---|---|---|---|---|---|---|
| STARTED | 3 | 3 | 3 | 2 | 2 | 2 |
| COMPLETED | 3 | 3 | 3 | 2 | 2 | 2 |
| NOT COMPLETED | 0 | 0 | 0 | 0 | 0 | 0 |
Second Intervention (2 Hours)
| Stage | Low Pressure, Reactive Support, Than Standard Mattress | Low Pressure, Standard Mattress, Than Reactive Support | Reactive Support, Low Pressure, Than Standard Mattress | Reactive Support, Standard Mattress, Than Low Pressure | Standard Mattress, Low Pressure, Than Reactive Support | Standard Mattress, Reactive Support, Than Low Pressure |
|---|---|---|---|---|---|---|
| STARTED | 3 | 3 | 3 | 2 | 2 | 2 |
| COMPLETED | 3 | 3 | 3 | 2 | 2 | 2 |
| NOT COMPLETED | 0 | 0 | 0 | 0 | 0 | 0 |
Third Intervention (2 Hours)
| Stage | Low Pressure, Reactive Support, Than Standard Mattress | Low Pressure, Standard Mattress, Than Reactive Support | Reactive Support, Low Pressure, Than Standard Mattress | Reactive Support, Standard Mattress, Than Low Pressure | Standard Mattress, Low Pressure, Than Reactive Support | Standard Mattress, Reactive Support, Than Low Pressure |
|---|---|---|---|---|---|---|
| STARTED | 3 | 3 | 3 | 2 | 2 | 2 |
| COMPLETED | 3 | 3 | 3 | 2 | 2 | 2 |
| NOT COMPLETED | 0 | 0 | 0 | 0 | 0 | 0 |
Analysis population for the primary outcome, as defined in the registry: Cross-over trial with 15 female participants between 60 and 80 years, each of them lied on every of the three types of mattress.
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.
Population: Cross-over trial. In total 15 participants, each of them lied on every of the three types of mattress.
| Characteristic | Unit | AlternatingLow Pressure Mattress,Reactive Mattress,Basic Foam |
|---|---|---|
| Participants analysed | 15 | |
| Age, Continuous | years | 66 (63 to 69) |
| Sex: Female, Male: Female | Participants | 15 |
| Sex: Female, Male: Male | Participants | 0 |
| Race and Ethnicity Not Collected | Participants | — |
| Region of Enrollment: Germany | participants | 15 |
| Body Mass Index (BMI) | kg/m2 | 24.5 (23.7 to 26.0) |
| Body temperature | °C | 36.3 (36.3 to 36.6) |
| Heart rate | beats per minute | 78 (66 to 80) |
| Systolic blood pressure | mmHg | 125 (115 to 140) |
| Diastolic blood pressure | mmHg | 75 (70 to 85) |
| Skin phototype: Skin phototype I | Participants | 3 |
| Skin phototype: Skin phototype II | Participants | 9 |
| Skin phototype: Skin phototype III | Participants | 3 |
6. Primary Endpoint
The registry lists the primary outcome as Transepidermal Water Loss (TEWL) in g/m2/h on Sacrum, at Baseline, measured over at baseline.
| Element | Registry entry |
|---|---|
| Result type | Median |
| Measure of spread | Inter-Quartile Range |
| Unit | g/m2/h |
| Endpoint classification | not reduced to a single comparison |
Transepidermal water loss (TEWL) measures water vapor passing from the body through the skin to the surrounding air. It is reported in g/m2/h and was measured with a Tewameter TM300. The registered primary outcome concerns the sacrum at baseline. The registry describes the summary measure as a median and the dispersion as an inter-quartile range.
General statistical and physiological context: TEWL is used as an indicator of skin barrier function. A higher or lower TEWL value can reflect differences in water movement across the skin, but interpretation depends on measurement conditions and the context of the study. TEWL is not itself a count of pressure ulcers, a diagnosis of tissue injury, or a direct measurement of later clinical events. It is a skin-property measure, which can help characterize a response to loading or a support surface when the relevant measurements and comparisons are reported.
The baseline values listed for the alternating low-pressure mattress, reactive support surface, and standard mattress are 7.8, 7.7, and 7.1, respectively. The registry also lists lower and upper values for each: 6.7 and 8.8; 6.7 and 8.2; and 6.8 and 8.8, respectively. These accompanying values are not identified as confidence intervals in the registry record. Because the named endpoint is baseline TEWL, these summaries alone do not describe a change after loading or an effect of one surface relative to another.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry reports a median baseline sacral TEWL of 7.8 for the alternating low-pressure mattress, 7.7 for the reactive support surface, and 7.1 for the standard mattress. Each surface is associated with 15 participants in the outcome record. The accompanying lower and upper values are also listed, but the record does not identify them as confidence intervals or explain their precise interpretation beyond describing the dispersion as an inter-quartile range. No separate spread value is listed.
These are descriptive summaries, not a reported treatment-effect estimate. In particular, the primary outcome is explicitly measured at baseline, before the loading period described in the study aim. The registry does not post a numerical comparison of post-loading TEWL between surfaces, a within-person change from baseline, or an estimate of a difference between any pair of surfaces. It therefore does not establish whether the surfaces produced different post-loading skin responses.
The three values are close in scale, but describing their numerical proximity is not equivalent to a statistical test. No standard error, confidence interval for a contrast, test statistic, or p-value for the primary outcome is reported in the registry record. Without a defined contrast and an inferential analysis, the precision of a surface-to-surface difference cannot be evaluated from these summaries. The listed lower and upper entries should not be treated as uncertainty bounds for a treatment effect.
The crossover structure also affects interpretation. Since each participant was measured on each surface, a comparison would ordinarily use paired or repeated measurements, with the participant serving as a basis for within-person comparison. The arm-level summaries do not show how each participant’s measurements varied across surfaces, and the registry does not report the analysis method used to account for the repeated observations. Separate medians do not preserve the pairing needed to reconstruct a within-person contrast.
The study’s broader aim was exploratory and concerned skin responses at two pressure-ulcer predilection sites, the heel and sacrum, following two hours of loading. The primary endpoint as posted is narrower: sacral TEWL at baseline. Other registered outcomes include skin-surface temperature at the sacrum and heel at several time points and erythema at the sacrum. Outcome listings indicate the scope of measurement, but they do not by themselves establish that results or statistical comparisons were posted for every listed measure. No inferential analysis entry is listed.
The appropriate reading is therefore limited to the recorded baseline distributions and the stated study design. They describe TEWL values in this small crossover sample; they are not evidence of a post-loading benefit or harm, a clinical pressure-ulcer outcome, or a causal difference among the surfaces. The registry record does not report results for a primary comparison after loading, and the baseline summaries do not substitute for such a comparison.
9. Statistical Methods Explained
The statistical interpretation starts with the measurement scale and the study structure. TEWL is a quantitative skin measurement reported in g/m2/h. The primary endpoint is summarized using a median, with the registry identifying the inter-quartile range as its dispersion measure. A median gives the middle value after observations are ordered. An inter-quartile range describes the spread of the central half of the observations. Those summaries can be useful when a distribution is skewed or when the mean and standard deviation would not represent a typical value and spread well. The registry does not give a separate inter-quartile range value in the posted primary summaries, so the dispersion cannot be fully read from those entries.
What do the baseline summaries say?
The listed medians are 7.8 for the alternating low-pressure mattress, 7.7 for the reactive support surface, and 7.1 for the standard mattress. Each is a summary of baseline observations associated with a surface. The registry also gives a lower and upper value for each surface. It does not label those entries as confidence intervals, and they should not be interpreted as such without that specification. A confidence interval has a particular inferential meaning: it expresses uncertainty about an estimated quantity under a statistical model and sampling procedure. A range of reported values, a quartile interval, and a confidence interval are not interchangeable.
These summaries do not provide a contrast estimate. A contrast would define which measurements are being compared, such as a within-participant change or a difference between two surfaces at a specified time. It would then quantify that comparison and, where appropriate, its uncertainty. Because the primary endpoint is at baseline and no contrast is posted, there is no primary treatment-effect estimate to interpret. The median values alone cannot answer whether loading on one surface led to a different response from loading on another.
Why does the crossover design matter?
General statistical explanation: In a crossover study, the same participant contributes measurements under multiple conditions. Measurements from one participant tend to be related because they share that person’s characteristics. A paired analysis uses the within-person relationship; a repeated-measures model can also represent that correlation and accommodate more complex measurement patterns. Such methods can be more appropriate than treating every observation as independent. The exact method depends on the design, endpoint, data completeness, and assumptions.
The registry says that each of the 15 participants lay on all three mattress types. That makes the individual-level pairing important for surface comparisons. Marginal summaries such as a median for each surface do not reveal the participant-level pattern. They do not show whether participants with higher values on one surface also tended to have higher values on another, nor do they permit reconstruction of a paired treatment contrast. The analysis method, participant-level data, exposure order, and any handling of carryover are not reported in the registry record.
General explanation of over-dispersion: Over-dispersion occurs when observed variability is greater than a statistical model assumes. It is most commonly discussed for count outcomes, where an overly restrictive variance assumption can make standard errors too small and apparent precision too high. The primary outcome is a continuous TEWL measurement, and the registry does not report a fitted model or a dispersion assessment. Over-dispersion is therefore not something that can be diagnosed from the posted median summaries. The broader lesson is that model assumptions should match the outcome and the dependence structure; whether any such checks were performed is not reported in the registry record.
What would uncertainty estimates mean?
General statistical explanation: A confidence interval for a treatment contrast describes the range of values compatible with the data and the specified statistical procedure, subject to its assumptions. It communicates precision as well as the direction and magnitude of an estimated contrast. It is not a probability statement that the true value lies in a particular interval after the data have been observed. A p-value, when reported, addresses compatibility with a specified null model and does not measure the size or clinical importance of an effect.
No confidence interval for a surface contrast and no p-value for the primary endpoint are reported in the registry record. The lower and upper values listed beside each median cannot fill that role because their inferential interpretation is not specified. Nor can an apparent difference between separate medians be treated as a tested difference, especially in a paired crossover design.
What can planning calculations establish?
General statistical explanation: A sample-size planning calculation asks how many participants or observations might be needed to detect a prespecified effect under stated assumptions about variability, significance level, allocation, and analysis. A calculation based on an effect observed in the same study is only an illustration of the implications of that estimate; it does not indicate the probability that the completed study detected a real effect. A study’s design justification and its analysis are separate matters.
The registry record does not report the trial’s sample-size justification, a target effect, or a power calculation used to plan enrollment. It also does not report a primary contrast from which a planning illustration could be meaningfully assessed. Thus, the enrollment of 15 is a recorded study characteristic, not evidence that the study was adequately powered or that it had a particular probability of detecting a surface difference. The intended statistical model, significance threshold, and planned handling of repeated measurements are not reported in the registry record.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists 94 outcome measures and 88 posted secondary outcomes. The listed secondary outcomes include skin-surface temperature at the sacrum and heel at baseline, after two hours of loading, and after off-loading, as well as sacral erythema measurements. The breadth of outcomes and time points makes it important to distinguish the registered primary endpoint from the other measurements. The primary endpoint is sacral TEWL at baseline; the registry record does not report a multiplicity-adjustment plan or explain how conclusions across multiple outcomes and time points were to be controlled.
Multiplicity arises when many hypotheses or outcomes are examined: the chance of at least one apparently notable finding can increase if each is assessed separately without an appropriate plan. General approaches can include prespecifying a hierarchy, adjusting inference, or clearly treating analyses as exploratory. Which approach was used in this trial is not reported in the registry record. The study description calls the overall aim exploratory, but that does not specify a particular multiplicity procedure.
Missing-data methods and the number of participants contributing to each outcome at each time point are not reported in the registry record. The primary summaries list 15 for each surface, but those entries do not establish completeness for every secondary outcome or time point. The record does not describe imputation, exclusions, or sensitivity analyses.
The analysis populations are also not defined in the registry record. Although the trial is randomized and crossover, the record does not say whether the analyses included all enrolled participants, only participants with complete measurements, or another set. The sequence allocation, carryover handling, and statistical model are not reported. These omissions limit assessment of how the posted outcome summaries relate to the intended crossover design.
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 |
|---|---|---|---|
| Alternating Low Pressure Mattress | 0 | 15 | 0.0% |
| Reactive Support Surface | 0 | 15 | 0.0% |
| Standard Mattress | 0 | 15 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Alternating Low Pressure Mattress | 0 of 15 |
| Reactive Support Surface | 0 of 15 |
| Standard Mattress | 0 of 15 |
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 |
|---|---|
| Alternating Low Pressure Mattress | 0 of 15 |
| Reactive Support Surface | 0 of 15 |
| Standard Mattress | 0 of 15 |
For each of the three surface groups, the registry lists 15 participants at risk for serious adverse events and zero affected by a serious adverse event. It also lists 15 at risk for other adverse events and zero affected by another adverse event in each group. The recorded death count is zero for each surface group. These are the adverse-event figures posted in the registry record.
A zero count means that no event in the listed category was recorded for the participants represented in that entry. It does not demonstrate that an event is impossible or that the surface has no risk. With a small study population, uncommon events may not occur during observation even if they could occur in other settings. The registry record does not provide further information about adverse-event definitions, ascertainment procedures, observation time for safety, or whether the same participants contributed to each surface entry as separate exposure periods.
These counts should be read as descriptive safety reporting, not as a comparative safety analysis. No statistical comparison of event rates is reported, and the crossover structure means the surface entries should not automatically be treated as independent groups. The zero counts do not establish equivalence among surfaces or rule out harms that were not captured or reported.
12. What the Result Does, and Does Not, Mean
The posted data establish that a randomized, unmasked crossover study enrolled 15 participants and assessed three support surfaces. The primary endpoint was sacral TEWL at baseline. Its listed medians were 7.8 for the alternating low-pressure mattress, 7.7 for the reactive support surface, and 7.1 for the standard mattress. The registry also identifies heel and sacral skin responses after two hours of loading as part of the broader study aim, with the sternum as a control area.
Those details do not amount to a finding that one surface changed skin function more than another. The primary endpoint is a baseline measure, and the registry record does not report a post-loading primary contrast or a within-person change. No inferential result for a surface comparison is listed. The values are descriptive summaries, and the accompanying lower and upper entries are not identified as confidence intervals. There is not enough posted information to determine the uncertainty around a treatment contrast.
The endpoint also has a specific scope. TEWL is a measure of water loss through the skin and is used as an indicator of skin barrier function. It is not a pressure-ulcer incidence outcome and cannot by itself establish whether a participant developed a pressure ulcer or whether a surface prevented one. The registry lists pressure ulcers as the condition, but the outcome described as primary is a skin-property measurement.
Likewise, the absence of recorded adverse events in the listed groups should not be read as proof of safety in all populations or settings. These counts describe events recorded among the study participants under the registry’s reporting. They do not establish that rare events cannot occur, nor do they provide a powered comparison of safety between surfaces.
The justified conclusion is bounded: the record describes the design, population, outcome scope, baseline TEWL summaries, and adverse-event counts. It does not report enough analysis to determine whether the support surfaces differed in post-loading skin response, whether any difference was clinically meaningful, or whether the study’s findings generalize beyond the participants and conditions studied. Those questions remain unresolved in the registry record.
13. Why This Trial Matters Statistically
This trial is statistically interesting because its crossover structure makes the choice of comparison especially important. Each participant lay on every surface, so measurements are repeated within people rather than drawn from three wholly separate groups. A valid surface comparison should preserve that pairing. Reporting a median for each surface describes each set of measurements, but it does not show how measurements changed within individuals or quantify the uncertainty of a paired contrast.
The endpoint also highlights the difference between a study’s broad scientific aim and its registered primary measure. The study aimed to assess skin responses at the heel and sacrum after two hours of loading, with the sternum as a control area. The primary outcome listed in the registry is instead sacral TEWL at baseline. Baseline skin function can describe the sample, but it does not itself estimate a response to loading. Clear alignment between the outcome time point and the question is necessary for readers to know what a result can answer.
The large set of registered outcome measures and secondary outcomes raises a further statistical issue: the interpretation of findings across multiple measurements and times depends on a prespecified analysis strategy. The record does not report such a strategy or an inferential analysis. Without those details, the posted summaries cannot establish which comparisons were intended to be confirmatory and which were exploratory.
These design features illustrate why transparent reporting matters alongside numerical results. Readers need to know the outcome time point, the paired-analysis method, uncertainty around contrasts, handling of missing measurements, and the approach to multiplicity. In their absence, careful interpretation should stay close to what is documented: descriptive baseline measurements and the study’s stated design, without inferring unreported comparative effects.
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 trial-specific limitations restrict interpretation of the registry results. First, the primary endpoint is sacral TEWL at baseline, while the broader study aim concerns responses after two hours of loading. The registry record does not provide a primary post-loading comparison or a change estimate. The posted baseline summaries therefore do not answer the stated question about skin response after loading.
Second, the study enrolled 15 participants, all female and aged 60 to 80 years according to the primary-outcome description. The findings, even if comparative results were available, would describe this study population and would not automatically generalize to people outside those characteristics. The registry does not report additional participant characteristics that might help assess representativeness.
Third, the crossover design depends on the order of exposure and the relationship between measurements from the same participant. The order of the three surfaces, washout or recovery procedures, and handling of potential carryover are not reported in the registry record. The analysis method is also not reported, so it is not possible to assess whether repeated measurements were handled in a way that reflects the design.
Fourth, the registry lists many outcome measures and secondary outcomes but does not report a multiplicity plan, missing-data methods, analysis populations, or inferential results for the primary measure. The primary summaries identify medians and dispersion as an inter-quartile range, but no separate dispersion value is posted and the lower and upper entries are not identified as confidence intervals. These limitations prevent assessment of the precision and robustness of a surface comparison.
Finally, the zero adverse-event counts are descriptive and arise from a small study. The registry record does not detail event definitions or ascertainment. They should not be treated as conclusive evidence about comparative safety or uncommon events.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Effects of Different Support Surfaces on the Properties Skin After Loading — NCT02930590.
- Registry record last updated 2022-06-14; status last verified 2022-05.
- Results first posted 2018-10-23.
- 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
NCT02930590 is a completed randomized, unmasked crossover study sponsored by Charite University, Berlin, Germany. The registry lists enrollment of 15 and describes 15 female participants aged 60 to 80 years, each of whom lay on an alternating low-pressure mattress with low-air-loss function, a gel mattress, and a basic-foam mattress.
The broader aim was to measure skin responses at the heel and sacrum after two hours of loading, with the sternum as a control area. The primary outcome is sacral TEWL at baseline, measured in g/m2/h with a Tewameter TM300. The listed medians are 7.8, 7.7, and 7.1 for the three surfaces, respectively. No inferential analysis entry is listed, and the registry record does not report a post-loading primary comparison.
The record lists 94 outcome measures and 88 secondary outcomes. It reports zero serious adverse events, zero other adverse events, and zero deaths in each surface group. Analysis methods, missing-data procedures, multiplicity handling, and sample-size justification are not reported in the registry record.