Evaluation of a Portable Oxygen Concentrator During Ambulation for Patients Who Require Supplemental Oxygen (POC-LEAN): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Evaluation of a Portable Oxygen Concentrator During Ambulation for Patients Who Require Supplemental Oxygen (POC-LEAN) (NCT04107493), a randomized na study. The primary outcome is Mean SpO2 (Oxygen Saturation) During Six Minute Walk Tests (6MWTs).

2. Clinical Question

The registry identifies mean SpO2 during six-minute walk tests as the primary endpoint. Its description says each subject’s SpO2 is measured during the test with each device. That framing makes the comparison about oxygen saturation recorded while walking under the two device conditions, rather than a comparison of longer-term outcomes.

The study is recorded as randomized and crossover. A crossover design generally means that participants receive or use more than one condition, so the comparison may involve measurements from the same participants under different conditions. The registry does not report the sequence, timing, or other details needed to describe precisely how the device conditions were administered. It also does not report whether the analysis used the within-participant structure. Those details should not be inferred from the design label alone.

3. Trial Design

The registry records POC-LEAN as a completed, prospective randomized study with a crossover design. The study status is completed, and the record lists an enrollment of 33. It identifies chronic obstructive pulmonary disease as the condition and names ResMed as the sponsor. The recorded start date is 2019-11-21, and the primary completion date is 2020-03-09.

The comparison is between a portable oxygen cylinder delivering continuous flow oxygen and the Mobi™ Portable Oxygen Concentrator. The registry describes the purpose as comparing Mobi™ with a continuous flow oxygen cylinder, using SpO2 as the primary endpoint. The outcome is mean SpO2 measured during a six-minute walk test. The record lists 33 participants for each device arm in the posted outcome summaries; because the design is crossover, those arm entries should not be interpreted as separate groups of participants without further information.

Randomized allocation is recorded, while masking is recorded as none. The registry does not report the randomization sequence, whether device order was balanced, the length of any interval between device conditions, or whether a washout period was used. It also does not report details of the test procedures, oxygen settings, or the conditions under which the walk tests were conducted. Such information could matter to interpretation, particularly if order, learning, fatigue, or carryover affected measurements.

The registry lists one outcome measure and no secondary outcome measures posted. It lists no analyses in its analysis count. Nonetheless, the primary outcome entry includes group means, standard errors, and a mean-difference estimate. The statistical procedures behind that contrast are not described in the registry record. The original protocol and sample-size assumptions are not reported in the registry record.

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: Participants acted as their own controls. Participants were randomised as to the order they used the devices during the 6-minute walking test. There was a one hour wash out period between tests

First Intervention (1 Hour)

Washout (One Hour)

Second Intervention

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: COPD adult patients with long term oxygen therapy history were included. They were all stable (at least 4 weeks since last exacerbation episode).

6. Primary Endpoint

The registry lists the primary outcome as Mean SpO2 (Oxygen Saturation) During Six Minute Walk Tests (6MWTs), measured over Mean Sp02, measured during 6 minute walk test.

The primary endpoint is mean SpO2, or peripheral oxygen saturation, measured during a six-minute walk test. SpO2 is expressed in the registry as a percentage of oxygen saturation. The outcome description says that each subject’s SpO2 is measured while taking the walk test under each device condition. The registry labels the summary as a mean and reports standard errors for the device groups.

As a continuous measure, mean SpO2 summarizes the average recorded saturation during the specified activity. Looking at the mean provides a concise way to compare the central level of the recorded measurements under the two devices. The standard error describes the statistical precision of an estimated mean; it is not a measure of the range of individual readings. Neither the mean nor its standard error, by itself, describes how readings varied from person to person or over the course of a test.

Using a walk test makes the endpoint relevant to the study’s stated focus on oxygen use during ambulation. It gives the comparison a defined activity context, rather than measuring saturation only at rest. The endpoint is still limited to the recorded oxygen saturation during the test. It does not, on its own, measure symptoms, comfort, mobility, sustained use, or longer-term outcomes. The registry does not report the sampling schedule for SpO2 during the walk test or how the measurements were combined into each subject’s mean. Those measurement details are not reported in the registry record.

7. Results Posted in the Registry

• Mobi™ Portable Oxygen Concentrator: mean 90.00 versus 91.20 on control; difference -1.20 (95% CI -3.14 to 0.74), standardized effect d = -0.30; z-test p = 0.225.

8. Statistical Interpretation

9. Statistical Methods Explained

The outcome is continuous: mean SpO2 during a six-minute walk test. For a continuous outcome, the group mean describes the average observed value, while a standard error describes the precision of that estimated mean. The standard error is not the standard deviation and should not be read as showing the spread of individual observations. The registry reports a mean and standard error for each device condition.

What does the mean difference represent?

The comparison is stated as Mobi™ minus the portable oxygen cylinder. A mean difference is the difference between the two reported means, expressed in the outcome’s units. The posted estimate is -1.2. Its negative direction reflects the lower posted mean for Mobi™ compared with the cylinder. The contrast communicates the estimated size and direction of the difference; it does not by itself indicate whether that difference is clinically important.

The interval around a mean difference represents a range of values compatible with the data and the statistical procedure used, under that procedure’s assumptions. A narrower interval indicates greater precision, while a wider interval indicates more uncertainty about the size of the difference. The registry reports bounds of -3.14 and 0.740. In interpretation, the fact that the interval extends across zero matters: zero is the value representing no mean difference. The record does not state the confidence level or provide enough methodological detail to identify all assumptions used to form the interval.

What does the p-value contribute?

The unadjusted p-value is 0.225. A p-value summarizes how compatible the observed result is with a specified null model, assuming the model and its test assumptions are appropriate. It is not the probability that the null hypothesis is true, and it does not measure the chance that the observed difference occurred “by chance.” It also does not convey the magnitude or practical importance of the estimate; the mean difference and interval are needed for those aspects of interpretation.

The word “unadjusted” indicates that the reported p-value is not presented as adjusted for other comparisons or covariates. The registry does not report whether any adjustment was planned or performed elsewhere. Since no secondary outcome measures are posted, the record does not establish the full set of analyses that may have been considered. Multiplicity handling is not reported in the registry record.

Why does crossover design matter?

In general, a crossover design can allow comparison of conditions within the same participant. Such comparisons can account for stable differences between participants, but valid analysis depends on the design and analysis details. The order of conditions, changes over time, period effects, and possible carryover from one condition to another may need consideration. These are general statistical concerns, not evidence that any such effect occurred in this study. The registry identifies the design as crossover but does not report the treatment sequence, timing, washout, or analysis model.

The posted outcome entries give means and standard errors by device, and the comparison entry gives a mean difference and interval. The registry does not say whether the contrast was estimated with a paired method, whether it accounts for within-participant correlation, or whether the standard errors reflect the crossover structure. It is therefore not possible to evaluate those analytic choices from the record alone. The result should be described using the posted statistics without attributing an unreported method to the investigators.

How should the estimates be read together?

The two group means describe the observed average SpO2 under the device conditions. The mean difference gives the estimated contrast on the same scale. The interval conveys uncertainty in that contrast, and the p-value gives a related test result. These statistics answer related but distinct questions. A p-value alone does not show precision; an interval alone does not establish clinical importance; and group means alone do not show how much individual readings varied.

The record does not report a clinically meaningful threshold for SpO2 differences in this setting. Without such a threshold, the statistical result cannot be translated into a judgment about practical importance. The record also does not report distributional checks, handling of outliers, missing-data methods, or a prespecified statistical analysis plan. Those are limitations in the available methodological description, not proof that the investigators did not consider them.

10. Confidence Intervals and Precision

The comparison estimate is a mean difference of -1.2 for Mobi™ relative to the portable oxygen cylinder. The registry reports an interval with a lower bound of -3.14 and an upper bound above zero. Since the interval spans zero, the data do not pin down the direction of the underlying mean difference with high precision. Values consistent with the interval include a lower mean under Mobi™ and a higher mean under Mobi™ relative to the cylinder.

The interval is more informative about uncertainty than the point estimate alone. The estimate of -1.2 is one central summary of the comparison, but it should not be treated as the exact underlying difference. The interval indicates that the observed data leave room for a range of possible mean differences under the method used. The registry does not report the confidence level for this interval, and the analysis method is not described in enough detail to assess its assumptions.

The standard errors for the posted means are 0.7 in each device condition. A standard error measures the precision of an estimated mean, not how far apart individual participants’ measurements may be. The individual-level distribution is not reported. In a crossover design, the precision of the comparison can depend on how paired observations relate to one another. The record does not state whether this dependence was used in calculating the interval.

The p-value of 0.225 is consistent with uncertainty in the estimated contrast, but it is not a substitute for the interval. Neither statistic establishes equivalence or rules out a difference that could matter. The record does not define an equivalence margin, a noninferiority margin, or a threshold for clinical importance. Thus, the result supports a cautious reading of the estimate and its uncertainty rather than a definitive claim about the devices’ comparative effects.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total events. This is a continuous-outcome comparison, rather than a time-to-event analysis. The illustrations use the observed effect as their reference and show planning for 100% of that effect, 75% of the observed effect, and 50% of the observed effect. For each assumed effect, the display gives the number of participants per arm for 80% power and for 90% power.

In plain language, the 80% power column gives an illustrative per-arm sample size for a design that would have an 80% chance of detecting the specified effect under the stated assumptions, if that effect were the true one. The 90% column gives the corresponding planning target for 90% power. The listed values are 177 and 236 for planning for 100% of the observed effect; 314 and 420 for planning for 75% of the observed effect; and 706 and 944 for planning for 50% of the observed effect.

These figures are based on a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is the stated fraction of the observed effect. As the effect assumed for planning becomes smaller, more participants are needed to detect it at the stated power levels. These are illustrative planning calculations based on the observed effect, not the trial’s original design assumptions. The original sample-size justification and assumptions are not reported in the registry record. This is not observed power.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -1.200; pooled standard deviation σ = 4.021.
2. n = 2 × (1.96 + 0.842)² × 4.021² / -1.200² = 176.3, rounded up to 177 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- -1.2                      # observed difference in means
sigma <- 4.02119385257662                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(4107493)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 177 (80% power), 236 (90% power)
 75% of observed effect: n per arm = 314 (80% power), 420 (90% power)
 50% of observed effect: n per arm = 706 (80% power), 944 (90% power)
power.t.test: 177.2 
Simulated power at n = 177 per arm: 0.800 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Multiplicity, Missing Data and Analysis Populations

The registry lists one outcome measure and no secondary outcome measures posted. It does not describe a multiplicity adjustment, a hierarchy of outcomes, or a prespecified approach to multiple testing. The reported p-value is labeled unadjusted. As a general statistical matter, when several outcomes or analyses are examined, the chance of obtaining a small p-value somewhere among them can increase unless the analysis plan accounts for the multiplicity. The registry record does not establish whether additional analyses were conducted beyond those posted.

Missing-data methods are not reported in the registry record. The outcome entry does not state whether all participants completed a walk test under both device conditions, how incomplete tests were handled, or whether any measurements were excluded. The record does not give the number of participants contributing to the outcome analysis beyond the arm entries. It also does not report sensitivity analyses for missing measurements. Consequently, the posted summaries do not show whether missingness could have influenced the contrast.

The analysis population is not defined. The record does not say whether the comparison used all enrolled participants, only those with measurements under both conditions, or another population. Although the registry reports an enrollment of 33 and lists 33 for each device condition, the crossover design means those entries should not be combined or treated as separate participant groups. The record does not explain exclusions, protocol deviations, or the handling of participants who may not have completed both device conditions.

The record identifies randomized allocation and a crossover model, but it does not report the statistical analysis plan, treatment sequence, period effects, or carryover assessment. These omissions limit assessment of multiplicity, missingness, and the relationship between the design and analysis. They do not establish that problems occurred; they indicate that the registry record does not provide the information needed to evaluate them.

14. 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 no serious adverse events and no other adverse events in either listed safety group. It also reports no deaths in either group. Each group entry lists 33 at risk for serious adverse events and 33 at risk for other adverse events. The safety groups are named Standard Oxygen Cylinder and Mobi.

These are counts as recorded in the registry. They indicate that no events in the reported categories were posted for the listed groups; they do not prove that the devices carry no risk. The registry does not provide event definitions, a safety observation period, details about how events were collected, or a narrative describing the safety assessment. It also does not explain whether participants contributed to both device conditions in the safety summaries or how any exposure time was handled.

The absence of reported events should therefore be interpreted in the context of the study size and available reporting detail. The registry’s safety entries do not characterize event rates beyond the posted counts, and they cannot address uncommon events or outcomes not included in the record. No medical recommendation follows from these safety counts.

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

The registry’s primary result is a comparison of mean SpO2 during six-minute walk tests under Mobi™ and portable continuous flow oxygen cylinder conditions. The posted means are 90.0 for Mobi™ and 91.2 for the cylinder. The mean difference for Mobi™ relative to the cylinder is -1.2, and the unadjusted p-value is 0.225. The interval extends from -3.14 to a value above zero, indicating uncertainty about the direction and size of the underlying mean difference.

This result does not establish that the devices are equivalent. Equivalence requires a defined margin and an analysis designed to evaluate whether the difference lies within that margin; neither is reported in the registry record. Nor does the result establish a clinically important difference, because the record does not report a threshold for clinical importance. A nonsignificant p-value should not be interpreted as proof that there is no difference.

The endpoint is also specific. It concerns mean SpO2 during a six-minute walk test and does not directly describe other aspects of device use, such as ease of carrying, comfort, symptoms, adherence, or longer-term experience. The registry does not post secondary outcomes that could address those questions. The result therefore should not be generalized to outcomes that were not reported.

The trial is recorded as randomized and crossover, but important details about the implementation and statistical analysis are absent. The record does not explain sequence, timing, carryover handling, or the analysis population. Those omissions limit assessment of how well the posted comparison accounts for the design. They do not invalidate the recorded values, but they constrain the strength of conclusions that can be drawn from them.

Overall, the posted data offer an estimate of the mean SpO2 contrast and show that its precision is limited. They do not provide a definitive answer about equivalence, clinical importance, or broader comparative performance. The interpretation should remain tied to the specified outcome, activity, study population, and registry reporting.

16. Why This Trial Matters Statistically

This trial illustrates why the point estimate, its uncertainty, and the study design need to be read together. The posted mean difference is -1.2, but the interval extends across zero. The point estimate gives a direction and magnitude for the observed contrast, while the interval shows that the underlying difference remains uncertain. Reporting only the means or only the p-value would leave out important information about precision.

The crossover label also highlights the importance of matching the analysis to the design. When participants experience more than one condition, within-participant measurements may be related. That relationship can affect the uncertainty of the comparison. The registry does not state whether the analysis accounted for paired observations or how it addressed possible period or carryover effects. This makes the record a useful example of how a design label, outcome summaries, and analysis details are all needed to evaluate a treatment contrast fully.

Planning figures further demonstrate that sample-size calculations depend on the effect researchers want to detect. The planning illustrations show larger per-arm requirements when the assumed effect is a smaller fraction of the observed effect. These values are not a reconstruction of the original design and do not show the study’s observed power. The original sample-size justification is not reported in the registry record.

Finally, registry results should be interpreted within their reporting boundaries. The primary endpoint is posted, but analysis populations, missing-data handling, multiplicity, and several measurement details are not. Recognizing these gaps helps distinguish what the data directly describe from questions that remain unanswered.

17. 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 registry record leaves important details of the crossover implementation unspecified. It does not report the order in which participants used the devices, the interval between conditions, whether a washout was used, or whether the walk-test procedure was standardized in a way that could be assessed from the record. These details could influence interpretation of measurements taken under sequential conditions, but the record does not establish that any influence occurred.

The description of the endpoint says SpO2 was measured during each subject’s six-minute walk test, but the measurement schedule and method for deriving each subject’s mean are not reported. The record does not state whether the reported means reflect repeated readings, a specific time point, or another summary of measurements across the test. Further participant characteristics, including details beyond the condition of COPD and the need for supplemental oxygen, are not reported in the outcome entry.

The registry provides means, standard errors, a mean difference, an interval, and an unadjusted p-value, but does not describe the analysis method. In particular, it does not state whether the mean-difference analysis used paired data or accounted for within-participant correlation. It also does not report handling of missing observations, exclusions, protocol deviations, or the analysis population. The analysis count is listed as zero even though outcome statistics and a comparison are posted, and the record does not explain that discrepancy in how analyses are represented.

The record does not report a clinically meaningful threshold, an equivalence or noninferiority margin, the trial’s original sample-size assumptions, or results for secondary outcomes. Safety reporting is limited to the posted adverse-event counts, without a stated observation period or event-collection details. These limitations restrict conclusions to the recorded primary outcome and the information available in the registry.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Evaluation of a Portable Oxygen Concentrator During Ambulation for Patients Who Require Supplemental Oxygen (POC-LEAN) — NCT04107493.
• Registry record last updated 2021-05-26; status last verified 2021-05.
• Results first posted 2021-05-26.
• 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.

21. Record Summary

POC-LEAN is recorded as a completed, prospective randomized crossover study sponsored by ResMed. The registry identifies chronic obstructive pulmonary disease as the condition and lists an enrollment of 33. It compares a portable oxygen cylinder delivering continuous flow oxygen with Mobi™ Portable Oxygen Concentrator.

The primary outcome is mean SpO2 during six-minute walk tests. The posted means are 91.2 for the cylinder and 90.0 for Mobi™, with a mean difference of -1.2 for Mobi™ relative to the cylinder. The reported interval extends from -3.14 to a value above zero, and the unadjusted p-value is 0.225.

The registry reports no serious adverse events, other adverse events, or deaths in either listed safety group. It does not report the original sample-size justification, detailed statistical methods, missing-data procedures, or further crossover implementation details.