N-Acetylcysteine for Patients With COPD and Chronic Bronchitis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for N-Acetylcysteine for Patients With COPD and Chronic Bronchitis (NCT01739790), a randomized na study. The primary outcome is Changes in the Saint George's Respiratory Questionnaire.

2. Clinical Question

3. Trial Design

This was a randomized, placebo-controlled, parallel-group trial with triple masking. The registry lists an enrollment of 51 and identifies the University of Minnesota as sponsor. The recorded start was 2013-01, the primary completion was 2015-12, and the current status is terminated. The reason for termination and the timing or circumstances of that decision are not reported in the registry record.

Random allocation is intended to make treatment groups comparable on average, including for characteristics that were not measured. It does not guarantee that groups will be identical, particularly in a small trial. The record does not describe the randomization sequence, allocation concealment, or the method used to maintain masking. Triple masking indicates that masking was used across multiple roles, but the specific roles are not reported in the registry record.

The intervention arm received N-acetylcysteine at 1800 mg twice daily for 8 weeks. The comparator arm received placebo pills described as identical in appearance and prescribed with the same frequency and duration. The record does not report whether participants could receive other care during the trial or how treatment adherence was assessed.

The primary outcome was change in Saint George’s Respiratory Questionnaire score from baseline to 8 weeks. The registry describes the outcome as a mean with standard deviation, but does not give the observed results or an analysis comparing the arms. Enrollment should not be read as the number of participants who completed treatment or contributed to the primary analysis; those analysis-population details 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

Reasons for not completing this period:

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 Changes in the Saint George's Respiratory Questionnaire, measured over Baseline to 8 weeks.

The primary endpoint was change in the Saint George’s Respiratory Questionnaire (SGRQ) from baseline to 8 weeks. The SGRQ is a self-administered measure of respiratory health status, scored from 1 to 100, with 100 representing the worst respiratory health status. Because higher scores indicate worse status on this scale, a lower score corresponds to better reported respiratory health status. The registry describes the outcome using a mean and standard deviation.

A questionnaire endpoint can capture how participants report the impact of respiratory symptoms and limitations, complementing measures focused only on clinical events or physiological function. A change score compares a participant’s later score with their baseline score; a comparison between randomized groups can then estimate whether average change differed by assigned treatment. General statistical interpretation depends on the direction convention used for change, the analysis population, and how missing questionnaires are handled. The direction convention and those analysis details are not reported in the registry record.

The record states the intended comparison in its brief summary, but the posted registry information does not include group means, an estimated between-group contrast, a confidence interval, or a test result for this endpoint. The size, direction, and precision of the observed primary-outcome effect therefore are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes randomization, a parallel-group comparison, triple masking, and a continuous primary outcome reported in terms of means and standard deviations. It does not report a detailed statistical analysis plan, a model for the primary comparison, the method for handling missing observations, or numerical primary-outcome results. The explanations below are general statistical context, not a description of methods confirmed for this trial unless explicitly stated.

What does randomization contribute?

In general, randomization assigns participants to treatment groups by chance. Its purpose is to reduce systematic differences between groups at the outset, so that a later contrast can be interpreted as an estimate of the effect of assignment, subject to adherence, missing data, and other features of the trial. Randomization does not ensure that every measured or unmeasured characteristic will be balanced in a small study. The registry does not describe how the random sequence was generated or concealed before assignment.

A parallel-group design assigns participants to a study arm and compares outcomes across arms. Here, the listed arms are N-acetylcysteine and placebo, and the treatment period is 8 weeks. The registry says the study was triple masked but does not identify which people or roles were masked, how masking was maintained, or whether masking was assessed. In general, masking can reduce the risk that expectations affect care, reporting, or assessment; it cannot remove every source of bias.

What do the mean and standard deviation describe?

For a continuous measure such as SGRQ score, the mean is a summary of the group’s average value or average change. The standard deviation describes how spread out individual values are around that mean. It is not the same as a confidence interval: a standard deviation describes variation among observations, while a confidence interval expresses uncertainty about an estimated quantity. The registry identifies mean and standard deviation as the outcome summary, but does not report their values for either arm.

A treatment comparison generally focuses on the difference between groups, rather than asking only whether change within one arm differs from baseline. The between-group estimate and its confidence interval would convey the estimated size and uncertainty of the contrast. The registry does not report such an estimate or interval, nor does it state whether the primary analysis compared endpoint scores, changes from baseline, or used an adjustment for baseline score. The named outcome is change from baseline, but the detailed calculation and model are not reported in the registry record.

Why does uncertainty matter?

In general, a confidence interval gives a range of values compatible with the data and the statistical model at a stated confidence level. A narrow interval indicates greater precision than a wide interval, while an interval spanning values in different directions may leave the direction of the effect uncertain. An interval should be interpreted alongside the size and clinical meaning of the estimated effect; statistical compatibility alone does not establish clinical importance. No confidence interval or stated confidence level for the primary outcome is reported in the registry record.

A p-value, when reported, measures how unusual data at least as incompatible with a null hypothesis would be under specified assumptions. It does not give the probability that the null hypothesis is true, nor does it measure the size or importance of an effect. No primary-outcome p-value or test procedure is reported in the registry record. The record also does not report a prespecified significance threshold for the primary analysis.

How should over-dispersion be understood?

General explanation: over-dispersion occurs when observed variability is greater than a statistical model expects. It matters especially for count outcomes, where a model assuming a fixed mean-variance relationship may understate uncertainty when counts vary more than expected. The primary outcome in this trial is described as a continuous questionnaire score summarized by a mean and standard deviation, not as a count outcome. The record does not report an over-dispersion assessment or a model that would require one.

For continuous outcomes, analysts still need to consider the distribution of scores, outliers, and whether model assumptions are reasonable. The standard deviation can help describe observed spread, but it does not by itself establish that a particular model is suitable. The registry does not provide outcome distributions, diagnostic checks, or a specified modeling approach, so these aspects cannot be evaluated from the registry record.

What do the planning illustrations represent?

The registry’s stated planning assumptions describe a two-sided significance level of 0.05, equal allocation, a normal approximation, and effects defined as a stated fraction of the observed effect. Such calculations are planning illustrations: they describe hypothetical participants per arm under assumptions, rather than the trial’s observed power. They do not show that an effect occurred, and they do not substitute for an observed estimate with an uncertainty interval.

The registry record does not report the primary-outcome effect used for these illustrations or provide numerical planning results in the information available for interpretation. Any such illustration is conditional on the effect assumption and analysis conditions; it should not be treated as a forecast of what a future trial will achieve. In particular, no conclusion about the adequacy of the original enrollment target or the reason for termination can be drawn from those assumptions.

10. Multiplicity, Missing Data and Analysis Populations

The registry indicates that the primary outcome has several categories or time points and is not reduced to one comparison. It does not specify which category or time-point comparisons were conducted, which were prespecified as primary, or whether any multiplicity adjustment was planned or used. When multiple outcomes or comparisons are examined, general statistical practice recognizes that the chance of at least one apparently unusual result can increase. Adjustment methods or a clearly defined hierarchy can address that issue, but the registry record does not report such a strategy.

The record does not report a statistical analysis plan or explain how the primary endpoint was selected for analysis. It also does not state whether analyses were based on assignment as randomized, treatment received, or another analysis population. These choices affect interpretation, particularly if participants discontinue, deviate from treatment, or have unavailable questionnaire assessments.

Missing outcome data can reduce precision and may bias a comparison if availability is related to treatment or health status. General approaches include assumptions about the missingness process, imputation, or sensitivity analyses; each requires methods and assumptions to be described. The registry record does not report the amount or pattern of missing SGRQ data, the method for handling missing observations, or sensitivity analyses. It is therefore not possible to assess how missing data may have affected the primary result.

The record does not report interim analyses, stopping rules, or a sample-size justification. These details should not be inferred from the terminated status. Nor does the registry information establish whether the outcome analysis followed a prespecified plan. The reported planning assumptions do not answer these questions.

11. 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.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: copd exacerbation (9.1%), pneumonia (4.3%).

The registry reports serious adverse events in the placebo arm among 22 participants at risk, with 2 affected, and in the N-acetylcysteine arm among 23 participants at risk, with 3 affected. It reports other adverse events among 22 participants at risk in the placebo arm, with 9 affected, and among 23 participants at risk in the N-acetylcysteine arm, with 13 affected. Deaths are recorded as 0 in each arm.

The registry lists COPD Exacerbation at 9.1% and Pneumonia at 4.3% among its top serious adverse-event terms. It does not specify in this record which arm or denominator these percentages refer to, so they should not be assigned to an arm or converted into a comparison. The record also does not provide event timing, severity detail beyond the serious-event classification, or individual event narratives.

These are descriptive counts, not evidence that treatment caused or prevented an event. The numbers at risk indicate the group sizes used for the adverse-event reporting, but do not establish the analysis population for the primary endpoint. The registry does not report a statistical comparison of adverse events or enough detail to evaluate differences in exposure or follow-up.

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

The registry record establishes the trial’s question, design, treatment schedule, primary measure, and selected adverse-event counts. It does not report the numerical primary-outcome findings. The central missing information is the comparison of SGRQ change between N-acetylcysteine and placebo, together with an uncertainty measure. Without those results, the direction, size, and precision of the treatment effect cannot be described from this record.

The stated hypothesis that N-acetylcysteine would improve SGRQ scores is not evidence that improvement occurred. Likewise, absence of a posted result is not evidence that the treatments had the same effect. A statistically non-significant result, if one existed, would not by itself demonstrate equivalence; an equivalence or non-inferiority claim requires a design and analysis suited to that question. The registry does not report such an analysis.

The safety entries provide counts of affected participants and named serious-event terms, but do not establish why events occurred or whether any difference was caused by treatment. A numerical imbalance in descriptive counts, by itself, is not a causal conclusion. The lack of reported event narratives and comparative analysis limits further interpretation.

The trial’s terminated status should also be kept separate from its results. The registry does not report the reason for termination, so it cannot be attributed to the intervention, safety, recruitment, or the observed outcome. The planned duration of 8 weeks and listed enrollment do not reveal how many participants posted primary-outcome data or how much follow-up was completed.

Overall, the record documents a randomized comparison and an outcome intended to reflect respiratory health status, but the outcome estimate needed to answer the efficacy question is not reported in the registry record. The available information supports describing the design and reported safety counts, not a conclusion that treatment works or does not work.

13. Why This Trial Matters Statistically

This trial raises a central issue in clinical-trial interpretation: a clear research question and randomized design are not enough to evaluate the treatment effect without the outcome estimate and its uncertainty. The registry specifies an SGRQ change from baseline to 8 weeks and identifies mean and standard deviation as summaries. Yet it does not report the arm-level results or a between-group contrast. Readers therefore cannot judge either the estimated difference or how precisely it was measured.

The distinction between a planned objective and an observed result is especially important. The registry’s description that high-dose NAC will improve scores states the hypothesis being tested. It does not establish that scores improved, that one arm performed better, or that any difference was clinically meaningful. Transparent reporting of estimates and uncertainty is necessary for those judgments.

The record also illustrates why outcome definition and multiplicity matter. It indicates that the primary outcome has several categories or time points without reducing them to one comparison. Without clarification of the comparisons and any analysis plan, it is difficult to identify which result was intended to carry the primary inferential weight. The registry does not report whether multiplicity was addressed.

Finally, a terminated status and planning assumptions can easily be overinterpreted. Neither explains the study’s outcome or reason for termination. Planning calculations are conditional illustrations, not observed power and not evidence that a treatment effect exists. Statistical reporting is most useful when it connects the design, analysis population, effect estimate, uncertainty, missingness, and safety observations in a way that allows readers to distinguish what was measured from what remains unknown.

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 in interpretation arise from what the registry does not report. It gives no group-level SGRQ changes, treatment contrast, confidence interval, or primary-outcome test result. The effect’s direction, magnitude, and precision therefore cannot be evaluated. Although the endpoint is defined as change from baseline to 8 weeks, the detailed calculation and statistical model are not described.

The registry does not report participant characteristics beyond COPD and chronic bronchitis, eligibility criteria, or baseline comparability. It also does not describe the random sequence, allocation concealment, masking roles, adherence, withdrawals, or protocol deviations. These omissions prevent assessment of how the planned design was implemented and how representative the enrolled group may have been.

Analysis-population definitions and missing-data information are absent. The number of participants with available primary-outcome data, the reasons for missing questionnaires, and any sensitivity analyses are not reported in the registry record. The entry for enrollment cannot substitute for these details. The record also does not specify which of the several outcome categories or time points were analyzed or how multiplicity was handled.

For safety, event counts are reported, but the registry does not describe event timing, follow-up completeness, or event-level detail. The listed serious-event percentages are not linked to an arm or denominator in the record. The reason for termination, interim monitoring, stopping rules, and sample-size justification are also not reported. These limits do not establish that a particular bias or problem occurred; they restrict what can be concluded from the registry information.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: N-Acetylcysteine for Patients With COPD and Chronic Bronchitis — NCT01739790.
• Registry record last updated 2017-09-13; status last verified 2017-08.
• Results first posted 2017-09-13.
• 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

NCT01739790 is a randomized, triple-masked, parallel-group, placebo-controlled trial sponsored by the University of Minnesota. It enrolled 51 people and is listed as terminated. The recorded start was 2013-01 and primary completion was 2015-12. The planned treatment was N-acetylcysteine at 1800 mg twice daily for 8 weeks, compared with matching placebo taken twice daily for 8 weeks.

The primary outcome was change in SGRQ score from baseline to 8 weeks. The scale ranges from 1 to 100, with 100 indicating the worst respiratory health status. The registry does not report a numerical primary-outcome comparison or explain why the trial was terminated. It records serious and other adverse-event counts by arm, and lists COPD Exacerbation and Pneumonia among the top serious terms. The posted information supports a description of the design and reported safety entries, but not a conclusion about the primary treatment effect.