Airway Limitation Study: Study In Primary Care Centers Of Chronic Bronchitis In Long-Term Cigarette Smokers Of At Least 40 Years Of Age With Symptoms Of Cough And Shortness Of Breath: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Airway Limitation Study: Study In Primary Care Centers Of Chronic Bronchitis In Long-Term Cigarette Smokers Of At Least 40 Years Of Age With Symptoms Of Cough And Shortness Of Breath (NCT00442468), a registered phase not stated study. The primary outcome is Number of Participants With a Post-bronchodilator FEV1/FVC <=70% Versus Participants With a Postbronchodilator FEV1/FVC >70%.

2. Clinical Question

3. Trial Design

NCT00442468, titled the Airway Limitation Study, was a completed, cross-sectional, non-interventional study sponsored by GlaxoSmithKline. The registry describes a study in primary care centers of long-term cigarette smokers aged 40 years and older who had symptoms of chronic bronchitis. Its stated purpose was to assess how often airflow obstruction was present in this setting and whether participants had spirometric findings consistent with COPD.

The study did not test a drug or other treatment. All enrolled participants were asked to complete a questionnaire and pulmonary function testing. The registry describes the primary outcome as post-bronchodilator FEV1/FVC categories. Spirometry was assessed before and 15-30 minutes after albuterol, which participants self-administered under supervision of trained site staff. The primary outcome population is specified as participants who completed both pre- and post-bronchodilator spirometry.

Enrollment was 1283. The recorded start was 2007-04, and primary completion was 2007-09; the study status is COMPLETED. The registry lists 25 outcome measures, including the primary spirometry outcome and secondary measures based on dyspnea, respiratory symptoms, general health, physical limitations, and emotional or activity-related responses. It lists no analysis entries. These record details describe the intended study and its listed outcomes, but do not supply the primary outcome counts or results for the secondary measures.

Because the study was cross-sectional and had no treatment intervention, it does not provide a randomized treatment-versus-control comparison. The registry record does not report further details about recruitment procedures, participant flow, or how many enrolled participants completed the spirometry required for the primary outcome.

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

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: All enrolled participants who completed pre- and post-bronchodilator spirometry

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 Number of Participants With a Post-bronchodilator FEV1/FVC <=70% Versus Participants With a Postbronchodilator FEV1/FVC >70%, measured over Day 1 of a 1-day Study; before and 15-30 min after albuterol (self-administered under supervision of trained site staff).

The primary endpoint counts participants in two categories defined by post-bronchodilator FEV1/FVC: a value <=70% and a value >70%. FEV1 is the volume of air expelled from the lungs in one second; FVC is the volume that can be forcibly exhaled after a full inspiration. Their ratio is a spirometric measure of airflow. The registry description identifies FEV1/FVC <=0.7 as a measure used to demonstrate airway obstruction characteristic of COPD.

The measurement was taken after bronchodilator administration, with spirometry also performed before albuterol. The recorded timeframe is Day 1 of a 1-day study, before and 15-30 minutes after albuterol, self-administered under supervision of trained site staff. The registry defines the primary analysis population as all enrolled participants who completed pre- and post-bronchodilator spirometry.

In a cross-sectional study, this endpoint is intended to describe how many participants in the studied group fall into each spirometric category. It is not a measure of change caused by a study treatment, since no treatment was tested. Although the endpoint definition is recorded, the numbers of participants in the two categories are not reported in the registry record. The proportion classified in either group, and the precision of such an estimate, therefore cannot be read from the posted results.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a cross-sectional outcome describe?

General statistical context. A cross-sectional study describes measurements collected in a defined study population rather than assigning participants to treatment groups and following them to compare treatment outcomes. Its results can characterize the measured group at the time of assessment. They do not, by themselves, establish that one exposure caused an outcome or that a treatment changed it.

For this study, the listed primary outcome assigns participants to one of two groups using post-bronchodilator FEV1/FVC. A count in each group would describe the observed distribution among participants with the required measurements. To interpret those counts as a prevalence estimate, the denominator must also be clear. The registry identifies the relevant population as participants who completed pre- and post-bronchodilator spirometry, but the number in that population and the two counts are not reported in the registry record.

Why define the spirometric threshold?

General statistical context. A threshold turns a continuous measurement into a category. This can make a result easier to report as counts, but it also means that the classification depends on the chosen cutoff and on how the measurement was obtained. The registry describes FEV1/FVC <=0.7 as a measure used to demonstrate airway obstruction characteristic of COPD. The primary outcome title uses categories of <=70% and >70%.

Using a categorical endpoint does not show the full distribution of the underlying ratio. Participants with different values can fall into the same category, while values on opposite sides of the cutoff are classified separately. The registry record does not report the distribution of continuous FEV1/FVC values, the number of participants near the threshold, or further information about how borderline or technically incomplete measurements were handled.

What would a confidence interval add?

General statistical context. An estimate from a sample is subject to sampling variability. A confidence interval is a way to express the uncertainty around an estimate under a specified method and its assumptions. For a proportion, an interval would help readers judge how precisely the study estimates the frequency of a finding in the population represented by the sample. It does not correct selection bias, measurement error, or missing data, and it does not mean that every value inside the interval is equally likely.

No primary outcome confidence interval is reported in the registry record. Because the outcome counts and the relevant denominator are also absent, the posted record does not allow a reader to assess the numerical estimate or its precision.

How should the planning illustrations be read?

General statistical context. A sample-size calculation asks how many observations might be needed to detect an effect under stated assumptions. The number depends on the assumed effect, significance level, allocation, and statistical method. If the assumed effect is smaller, a larger study may generally be needed to detect it under otherwise unchanged assumptions; this is a general property of study planning, not a result from this study.

The registry describes its illustrations as based on the observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and effects expressed as stated fractions of the observed effect. It also states that the illustrations are not the trial’s own design. The record does not report the illustration values or the effect estimate used for them. Because the actual study is non-interventional and does not have two randomized arms, these planning assumptions should not be read as a description of the study’s enrollment plan. A planning sample size is not observed power, and it cannot recover missing outcome results.

What does over-dispersion mean in general?

General statistical context. Over-dispersion occurs when observed variability is greater than a statistical model expects. When a model assumes less variation than the data contain, standard errors can be too small and confidence intervals too narrow. It can also affect tests of statistical significance. Whether over-dispersion is relevant depends on the outcome and the model being used; it is not an automatic feature of every count or proportion.

The registry record does not report a statistical model for the primary outcome, a dispersion assessment, or analyses that would permit judging over-dispersion. The endpoint is described as participant counts in categories, but no model-based estimates are presented. It would therefore be inappropriate to infer that a particular adjustment was necessary or applied.

What does the analysis record establish?

The registry lists 25 outcome measures and zero analysis entries. This indicates that outcome topics are listed while analysis details and results are not available in the record. The record does not report the statistical methods used to produce primary or secondary estimates, any covariate adjustment, hypothesis tests, or confidence intervals. These omissions prevent readers from checking how the endpoint was analyzed or whether analyses followed a prespecified plan.

For an interpretable report of this endpoint, readers would need the number eligible for the primary outcome, the counts in both spirometric categories, and the method used to quantify uncertainty. Additional information about incomplete tests and the handling of missing measurements would help assess whether the analyzed participants differ from those enrolled. Those details are not reported in the registry record. The available design description and endpoint definition can explain what was intended to be measured, but they cannot substitute for the missing analysis and numerical findings.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 25 outcome measures, including the primary spirometric classification and secondary questionnaire outcomes. When a study examines multiple outcomes or makes multiple statistical comparisons, the chance of at least one apparently notable result can increase. Statistical approaches to multiplicity can address that issue, but the appropriate approach depends on the planned questions and analyses. The registry record does not report whether multiplicity was considered, whether any outcome was designated as a formal primary analysis beyond the listed endpoint, or whether any adjustment was used.

The record lists zero analysis entries. It does not report an analysis plan, test results, confidence intervals, or details of any secondary analyses. The listed secondary outcomes cover dyspnea, respiratory questionnaire responses, general health, activity limitations, and emotional or work-related limitations. Their numerical results and the methods used to analyze them are not reported in the registry record.

The primary outcome population is defined as enrolled participants who completed both pre- and post-bronchodilator spirometry. The registry reports enrollment of 1283, but does not report how many completed the required testing or how missing or unusable measurements were handled. It also does not report whether participants with incomplete questionnaires were included in secondary outcome analyses, or how missing questionnaire responses were treated.

The registry record does not report whether analyses used all enrolled participants, only participants with complete measurements, or another analysis population for each outcome. It does not report interim analyses, a missing-data strategy, or sensitivity analyses. Without those details and the outcome counts, the impact of missing measurements on the estimates cannot be assessed. The primary population definition should therefore not be mistaken for a complete account of participant flow or analytic methods.

11. 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 1% reporting threshold.

Most frequent non-serious adverse event terms

The registry lists 1283 participants at risk for serious adverse events and records zero serious adverse events. It also lists 1283 participants at risk for other adverse events and records 18 other adverse events. These are the posted counts; they should be read as separate registry categories rather than combined into a single measure.

The study is described as non-interventional and did not test a drug treatment. The record does not establish that the listed other adverse events were caused by a study procedure or by any treatment. It also does not report event descriptions in the available safety summary, the number of participants with each event, or further information about collection and classification procedures. Deaths are not reported in the registry record.

A count of zero serious adverse events is a statement about the events recorded in the registry, not proof that no event could occur or that every participant had complete safety follow-up. The record does not report additional follow-up details that would allow that interpretation. The 18 other adverse events likewise cannot be interpreted as a risk estimate without further information about their definitions and ascertainment. Since this was not a treatment comparison, the safety counts do not compare intervention and control groups.

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

The study’s documented aim was to assess airflow obstruction consistent with COPD among people with a history of cigarette smoking and symptoms of chronic bronchitis in a primary care setting. Its primary outcome used post-bronchodilator FEV1/FVC categories, and its other listed outcomes included questionnaire measures of respiratory symptoms, dyspnea, health, and limitations in activities.

The registry record does not report the counts for the primary outcome or numerical results for the secondary outcomes. As a result, it does not establish how common the spirometric classification was in the enrolled group. Enrollment of 1283 does not fill that gap: the primary analysis population was those who completed pre- and post-bronchodilator spirometry, and that denominator is not reported. Nor does the record provide a confidence interval or other numerical measure of uncertainty for the primary outcome.

The study was observational and cross-sectional, with no treatment intervention and no randomized comparison. Its design can describe measurements in the participants assessed, but cannot establish that smoking history or symptoms caused an individual spirometric finding, or that a treatment changed that finding. Generalization beyond the participants studied would also depend on how participants were selected and how representative they were; recruitment and representativeness details are not reported in the registry record.

The listed endpoint definition is useful for understanding what the study intended to count. It is not itself a finding. The posted information also does not report individual diagnoses, continuous lung-function distributions, or clinical outcomes. Accordingly, the record supports understanding the study’s design and measurement framework, but not a numerical conclusion about prevalence, precision, subgroup patterns, or causal effects.

13. Why This Trial Matters Statistically

This study is statistically notable for asking a descriptive question in a primary care population rather than testing an intervention. That distinction affects what an estimate would mean. A cross-sectional count of participants meeting a spirometric threshold can describe the measured group, while a randomized treatment comparison is designed to estimate differences attributable to assigned interventions. The record describes the former, not the latter.

The endpoint also illustrates the difference between a measurement and a classification. FEV1/FVC is a continuous ratio, while the primary outcome places participants into categories using a stated threshold. Categorical results may be straightforward to communicate, but their interpretation depends on the cutoff and on the completeness and quality of measurement. The registry gives the threshold and measurement timing, but does not report the category counts, distribution of the underlying ratio, or details of measurement completeness.

For a prevalence question, the denominator is as important as the numerator. The registry reports enrollment of 1283 but defines the primary outcome population as participants completing pre- and post-bronchodilator spirometry. Because the number in that outcome population is not reported, neither the observed frequency nor its precision can be determined from the record.

The study also lists a range of questionnaire outcomes. This underscores why analysis details matter: multiple measures can address different dimensions of symptoms and health, but readers need results and a clear account of analyses to interpret them. The registry lists 25 outcomes and zero analysis entries. Its record therefore identifies what was to be assessed without presenting the numerical evidence needed to evaluate the findings.

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 most immediate limitation of the registry record is the absence of numerical primary outcome results. It does not report the count with post-bronchodilator FEV1/FVC <=70%, the count with values >70%, or the number completing the spirometry needed for the primary outcome. Without these quantities, the main descriptive estimate and its precision cannot be assessed.

The record does not report participant flow, reasons for non-completion, or how incomplete or unusable spirometry was handled. Because the primary outcome population is restricted to participants completing pre- and post-bronchodilator testing, the difference between total enrollment and the analyzed population is important, but not quantified. The record also does not provide the numerical results for the listed questionnaire outcomes.

Further statistical details are not reported in the registry record, including the analysis methods, confidence intervals, any adjustment for multiple outcomes, and any sensitivity analyses. Interim analyses, a missing-data strategy, and the statistical analysis plan are also not reported in the registry record. These absences make it impossible to evaluate the choices underlying the estimates or to compare the posted outcome definitions with a fuller analysis plan.

Finally, the study is described as cross-sectional and non-interventional. Its design does not provide a randomized treatment comparison or establish causal effects. The registry record does not report additional recruitment or representativeness details that would support judging how closely the participants reflect other populations. These limitations concern what can be concluded from the recorded information; they do not supply an alternative result.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Airway Limitation Study: Study In Primary Care Centers Of Chronic Bronchitis In Long-Term Cigarette Smokers Of At Least 40 Years Of Age With Symptoms Of Cough And Shortness Of Breath — NCT00442468.
• Registry record last updated 2013-01-10; status last verified 2012-10.
• Results first posted 2010-01-07.
• 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.

18. Record Summary

NCT00442468 was a completed, cross-sectional, non-interventional study sponsored by GlaxoSmithKline. It enrolled 1283 people with a history of cigarette smoking and symptoms of chronic bronchitis in a primary care setting. Participants were asked to complete a questionnaire and pulmonary function testing; no drug treatment was tested.

The primary outcome classified participants by post-bronchodilator FEV1/FVC, using categories of <=70% and >70%. The primary outcome population was defined as enrolled participants completing pre- and post-bronchodilator spirometry. The registry lists 25 outcome measures and zero analysis entries. It records zero serious adverse events and 18 other adverse events among 1283 participants at risk for each category.

The primary outcome counts, secondary outcome results, analysis methods, and missing-data procedures are not reported in the registry record. The record therefore describes the study design and intended measures, but does not provide the numerical findings needed to assess the study’s primary prevalence estimate or its precision.