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 Reproducibility of 6 Minute Walk Tests for Oxygen Desaturation (NCT00740220), a registered phase not stated study. The primary outcome is Kappa Statistic for Correlation of the Oxygen Saturation Across 3 Serial 6 Minute Walk Tests (6MWT).
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00740220 |
| Phase | Phase not stated |
| Condition | Hypoxemia, Anoxia, Chronic Obstructive Pulmonary Disease |
| Allocation | Not Stated |
| Design model | Not Stated |
| Masking | Not Stated |
| Enrollment | 97 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Wake Forest University Health Sciences |
| Results posted | Yes |
2. Clinical Question
Population
The registry record lists hypoxemia, anoxia and chronic obstructive pulmonary disease as conditions. Enrollment was 97. It does not specify the characteristics used to select participants, provide a detailed participant profile, or state the primary outcome population.
Intervention
There is no treatment intervention described. Each participant was to perform three 6 minute walk tests, with all three intended to take place within 30 days. The study asks whether repeated tests yield reproducible oxygen desaturation measurements.
Comparator
The design is described as single arm, with each participant serving as their own control. The comparison is therefore among repeated tests within a participant, rather than between separate treatment groups. Allocation is not stated.
Primary question
The primary outcome is a kappa statistic for oxygen saturation across the three serial tests. In general, reproducibility concerns whether repeated measurements under comparable conditions agree sufficiently. The registry record does not state a threshold for acceptable reproducibility or report the observed kappa statistic.
3. Trial Design
This completed study is registered as a single-arm prospective observational study. The registry lists enrollment of 97 and identifies Wake Forest University Health Sciences as the sponsor. The listed start was 2006-09, and primary completion was 2009-01. The conditions named in the record are hypoxemia, anoxia and chronic obstructive pulmonary disease.
The design uses repeated measurements within the same participant: each participant was to perform three 6 minute walk tests, and each participant was to serve as their own control. The registry specifies that all three tests should take place within 30 days. This setup focuses on within-participant reproducibility rather than a treatment effect between randomized groups. Allocation is not stated, and the record does not describe a separate control arm for a like-for-like comparison.
The record identifies one outcome measure and describes it as the kappa statistic for correlation of oxygen saturation across the serial tests. It does not provide a detailed protocol for conducting the tests, the schedule between individual tests, the method of measuring or classifying oxygen saturation, or the criteria used to define desaturation. Those details are not reported in the registry record.
The registry status is completed, but completion does not establish that every enrolled participant contributed all planned measurements or that an analysis was performed. The record contains no analysis entries and does not report a result for the primary outcome. Reasons for any difference between enrollment and the number listed in the adverse-event information 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.
Overall Study
| Stage | Single Arm Prospective Observational Study |
|---|---|
| STARTED | 97 |
| COMPLETED | 88 |
| NOT COMPLETED | 9 |
Reasons for not completing this period:
| Reason | Single Arm Prospective Observational Study |
|---|---|
| screen failures (non-COPD patients) | 9 |
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 | Single Arm Prospective Observational Study |
|---|---|---|
| Participants analysed | 97 | |
| Age, Categorical: <=18 years | Participants | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 45 |
| Age, Categorical: >=65 years | Participants | 52 |
| Age, Continuous | years | 70 (SD 11) |
| Sex: Female, Male: Female | Participants | 60 |
| Sex: Female, Male: Male | Participants | 37 |
| Region of Enrollment: United States | participants | 97 |
6. Primary Endpoint
The registry lists the primary outcome as Kappa Statistic for Correlation of the Oxygen Saturation Across 3 Serial 6 Minute Walk Tests (6MWT), measured over All three 6MWTs should take place within 30 days.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | Ratio |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is titled “Kappa Statistic for Correlation of the Oxygen Saturation Across 3 Serial 6 Minute Walk Tests (6MWT).” Its unit is listed as a ratio, and the registry describes kappa as a measure of the quality of a test. The measurement is intended to summarize how consistently oxygen saturation is classified or recorded across repeated walk tests for the same participant. The planned timeframe is for all three tests to take place within 30 days.
In general, repeated-measurement reproducibility matters when a test is intended to give comparable results under comparable conditions. A summary statistic can help describe the degree of agreement across repeat assessments rather than relying on a collection of separate readings. Kappa is commonly used to summarize agreement while accounting for agreement expected by chance; its interpretation depends on how the measurements are defined and categorized.
The record does not explain how oxygen saturation was turned into the categories needed for a kappa calculation, which kappa formulation was used, or how missing or incomplete test sequences were handled. It does not provide the estimated statistic, its uncertainty, or a threshold for interpreting the result. Thus, the endpoint’s intended role is identifiable, but its numerical result and practical interpretation are not reported in the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry describes a question about measurement reproducibility, not a randomized treatment comparison. Each participant was to perform three 6 minute walk tests, with the participant serving as their own control. The stated primary outcome is a kappa statistic for oxygen saturation across those tests. This design makes within-participant agreement the central statistical issue.
The registry record does not report the kappa estimate, a confidence interval, a p-value, or any other numerical analysis result. It therefore does not establish, from the record alone, how much agreement was observed or how precise an estimate might be. The record also does not state a benchmark for acceptable agreement. A completed status and an enrollment figure are not substitutes for an outcome estimate.
In general, an estimate describes the observed pattern in the analysed data, while a confidence interval describes uncertainty around that estimate under the analysis assumptions. A narrow interval would indicate greater precision than a wide interval, but neither an interval nor an estimate is reported for this primary outcome. Without these results, no conclusion about the direction or degree of reproducibility can be drawn from the registry record.
The repeated-test structure can be useful for studying consistency because comparisons are made within participants rather than between separate groups. However, repeated assessments can still vary because of measurement conditions, participant state, test conduct, or other sources of variation. The record does not provide enough information to distinguish those sources or determine whether conditions were standardized between tests.
The record lists one outcome measure and no analysis entries. It does not report a statistical analysis plan, the handling of incomplete repeated tests, or an analysis population. Accordingly, the posted record supports describing the study question and intended endpoint, but not estimating the finding, its precision, or its robustness. It also cannot support a treatment-effect interpretation: the design described is not a randomized comparison, and no treatment contrast is reported.
9. Statistical Methods Explained
What does reproducibility mean?
In general, reproducibility concerns whether repeated measurements made under comparable conditions give sufficiently similar results. It is distinct from asking whether a measurement is associated with another variable, and it is also distinct from asking whether a treatment changes an outcome. For this study, the registry frames the question around oxygen saturation readings across repeated 6 minute walk tests in the same participant.
Repeated measurements from one participant are related rather than independent observations. In general, an analysis should account for that relationship. Treating every test result as if it came from an unrelated participant can misrepresent the information in the data and can produce misleading uncertainty. The within-participant setup is appropriate to the stated reproducibility question in concept, but the registry record does not specify the statistical model or calculation used beyond naming a kappa statistic.
What does kappa summarize?
In general, kappa summarizes agreement between classifications and adjusts the observed agreement for agreement that could occur by chance under its assumptions. It is not simply a correlation coefficient: correlation can describe whether measurements move together, while agreement asks whether they give similar classifications or values. The registry outcome title refers to correlation, while its description calls kappa a measure of test quality. The record does not clarify the exact operational definition used for this endpoint.
Kappa generally requires a defined set of categories or ratings. Its value can depend on how those categories are formed and on how frequently each category occurs. The registry record does not report the oxygen-saturation categories, the coding rules, the specific kappa method, or how the three repeated measurements entered the calculation. These omissions prevent a reader from checking the calculation or applying a detailed interpretation framework to the outcome.
Why does uncertainty matter?
In general, a point estimate gives a single summary of the observed data, but it does not show how much that estimate might vary across comparable samples. A confidence interval communicates statistical uncertainty around an estimate under a specified method and assumptions. A p-value addresses a different question, usually how compatible data are with a specified null hypothesis under a model. Neither measure replaces the estimate itself, and neither alone establishes practical importance.
No estimate, confidence interval or p-value for the primary endpoint is reported in the registry record. The record also does not identify a null hypothesis, a decision threshold for reproducibility, or a planned approach to uncertainty estimation. Interpretation is therefore limited to the endpoint’s stated purpose and the study structure.
How should the repeated-test schedule be read?
The outcome timeframe says that all three tests should take place within 30 days. In general, a bounded interval between repeated assessments can make the intended comparison more interpretable by limiting the span over which conditions may change. But the registry does not state the exact spacing between tests, whether the same procedures or equipment were used, or what circumstances could lead to postponement or exclusion. The timeframe alone does not establish that testing conditions were identical.
What do planning calculations mean?
In general, sample-size calculations are planning tools based on specified assumptions about an effect, variability, allocation and statistical method. A planning illustration is not an observed result and should not be described as observed power. The planning assumptions associated with this record describe a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and effects defined as fractions of an observed effect. They also distinguish total events for time-to-event calculations from participants per arm for other calculations.
Those assumptions do not describe the study’s stated single-arm, within-participant design. The record does not report a sample-size justification for the actual design, and no planning output should be treated as an analysis of this study. The registry record does not explain a connection between the two-arm planning assumptions and the single-arm study description.
What cannot be recovered from the registry record?
The record does not report an analysis method, missing-data rules, an analysis population, a precision estimate, or a result. It also does not explain whether the planned three tests were completed for each participant. Without those details, the endpoint can be described, but the statistical evidence for reproducibility cannot be reconstructed from the registry record.
10. Multiplicity, Missing Data and Analysis Populations
The registry record identifies one outcome measure, the kappa statistic for oxygen saturation across three serial 6 minute walk tests. It does not list analysis entries or report results for the primary outcome. No multiplicity strategy—such as a hierarchy of outcomes or adjustment for multiple statistical tests—is reported in the registry record. Because the record lists one outcome measure, it is not possible to determine whether additional analyses were planned but not included in the registry entry.
Missing-data handling is not reported in the registry record. In particular, the record does not state how an incomplete set of repeated tests would be treated, whether participants with fewer than three tests could contribute to an analysis, or how missing oxygen saturation measurements would be addressed. The reason that the adverse-event information lists 88 at risk, while enrollment is 97, is also not reported in the registry record; these figures should not be reconciled by assumption.
The analysis population is not reported in the registry record. There is no statement identifying whether the intended analysis included all enrolled participants, only those who completed all three tests, or another defined group. The record also does not report an interim-analysis plan, an analysis protocol, or a sample-size justification for the within-participant design. As a result, the completeness and selection of the data underlying any estimate cannot be assessed from the registry record.
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 |
|---|---|---|---|
| Single Arm Prospective Observational Study | 0 | 88 | 0.0% |
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 |
|---|---|
| Single Arm Prospective Observational Study | 0 of 88 |
The adverse-event information lists a single-arm prospective observational study group. It reports 88 participants at risk for serious adverse events and 0 affected. For other adverse events, it also reports 88 at risk and 0 affected. No top serious adverse-event terms are listed. The death count is null; that is not the same as a reported count of zero.
These figures are descriptive registry entries. They do not provide event definitions, the period of safety follow-up, the method for collecting events, or a narrative explaining how the figures were assembled. The record does not explain why the number at risk differs from the enrollment figure of 97, so no reason should be inferred. Nor does a zero affected count establish that no events occurred outside the reporting approach or period represented in the registry entry.
The study is described as a single-arm observational study, not as a comparison of treatment groups. These safety figures therefore do not support a comparative safety conclusion. They should be read as the reported counts in the registry, alongside the limits of the information recorded there.
12. What the Result Does, and Does Not, Mean
The study’s stated purpose is to assess whether oxygen saturation across three serial 6 minute walk tests is reproducible. The repeated-test design, with each participant serving as their own control and the tests intended to occur within 30 days, is aligned with a within-participant measurement question. The primary endpoint is identified as a kappa statistic.
What the record does not establish is the actual degree of reproducibility. It does not report the kappa estimate, its uncertainty, a hypothesis test, or a threshold for judging the result. Therefore, the registry record cannot show whether agreement was high, low, or estimated precisely. The status “completed” indicates the registered study status, not that a particular statistical conclusion was reached or posted.
The record also does not establish why any variation between tests might occur. In general, repeated measurements can differ because of the measurement process, testing conditions, participant variation, or other factors. The registry entry does not provide enough protocol detail or analysis information to separate these possibilities.
This is not a randomized treatment comparison. The single-arm design described in the record is not a basis for attributing a change to a treatment, and the reported endpoint concerns measurement consistency rather than a treatment effect. The adverse-event figures are limited registry counts, not comparative evidence. No medical conclusion should be drawn from the absence of a reported primary result.
The most defensible reading is narrow: the registry records a completed observational study with a planned repeated-measurement endpoint, but it does not report the analysis needed to judge the endpoint. A fuller interpretation would require a reported estimate, a description of its calculation, and information about the analysed participants and missing repeated tests.
13. Why This Trial Matters Statistically
Reproducibility is a statistical property of a measurement process. Before a measure can be interpreted as a stable basis for comparisons, researchers need to understand how similar results are when the same people are assessed repeatedly under comparable conditions. A study focused on repeatability therefore addresses a methodological question that is separate from whether an intervention changes a clinical outcome.
This trial’s design makes that distinction visible: each participant was intended to complete three 6 minute walk tests, serving as their own control, with the tests planned within 30 days. Such repeated observations can support a within-person assessment, but the result depends on how the measurements are defined, how the repeated data are analysed, and how incomplete test sequences are handled.
The registry’s naming of a kappa statistic also highlights the importance of matching a method to the data and question. In general, agreement statistics require clear operational definitions. A reader needs to know what counts as agreement, how measurements were categorized, and how uncertainty was quantified. Those details are not reported in the registry record, and the primary estimate is not reported either.
The statistical importance of the record is therefore partly in the question it sets out, and partly in the limits of what a registry entry can establish without results. The study is listed as completed, yet the record does not provide an analysis of its central outcome. That gap prevents evaluation of the observed reproducibility and illustrates why registration details and posted results serve different purposes.
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.
The registry record provides limited detail about the test procedures and statistical analysis. Although it identifies three repeated 6 minute walk tests within 30 days, it does not report the exact timing between tests, whether procedures were standardized, or how oxygen saturation readings were defined and recorded. The categories required for the named kappa statistic are not described.
No primary outcome estimate or uncertainty measure is reported. The record contains no analysis entries and does not identify the analysis population, the handling of incomplete test sequences, or the rules for missing measurements. It is therefore not possible to assess whether the outcome analysis, if conducted, included participants with all planned tests or a different group.
The registry does not report a sample-size justification for the single-arm repeated-measurement design. Planning assumptions describe equal allocation between two arms and a normal approximation, while the study itself is described as single arm and each participant as their own control. The record does not explain how those planning assumptions relate to the study design. Planning illustrations are not observed findings.
The enrollment figure is 97, while the adverse-event group lists 88 at risk. The registry record does not explain this difference, so it cannot be attributed to exclusions, follow-up, or incomplete testing. The record also does not report event definitions or a safety follow-up period. These are limits of what can be concluded from the registry entry, rather than evidence of a particular problem in study conduct.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Reproducibility of 6 Minute Walk Tests for Oxygen Desaturation — NCT00740220.
- Registry record last updated 2017-12-15; status last verified 2016-04.
- Results first posted 2009-04-20.
- 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.
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18. Record Summary
The registry describes a completed, single-arm prospective observational study sponsored by Wake Forest University Health Sciences. Enrollment was 97; the listed start was 2006-09, and primary completion was 2009-01. The conditions named are hypoxemia, anoxia and chronic obstructive pulmonary disease.
Each participant was to serve as their own control and perform three 6 minute walk tests within 30 days. The primary outcome is a kappa statistic for oxygen saturation across those tests. The registry record does not report the estimate, its uncertainty, or an analysis. It lists 88 at risk and 0 affected for both serious and other adverse events; the death count is null. The reason for the difference between enrollment and the safety group count is not reported in the registry record.