Gemfibrozil for Nicotine Smoking Cessation: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Gemfibrozil for Nicotine Smoking Cessation (NCT02638597), a randomized phase 2 study. The primary outcome is Exhaled Carbon Monoxide (CO).

2. Clinical Question

3. Trial Design

This was a randomized, parallel-group Phase 2 trial sponsored by the University of Texas Southwestern Medical Center. The registry lists an enrollment of 16 and describes two arms: Gemfibrozil and Waitlist. Each arm has 8 participants in the posted outcome data. The study is marked completed.

Participants in both arms received smoking cessation counseling. The Gemfibrozil arm also received gemfibrozil 600 mg twice daily by mouth for 9 weeks, beginning one week before the target quit date. The Waitlist arm received no medication during the trial. The registry says that after completing the trial without medication, participants who continued to smoke and wished to quit could choose to enter the gemfibrozil arm.

The registry lists masking as none. It does not report details of the randomization procedure, such as how the allocation sequence was generated or concealed. The record gives a start date of 2015-02 and a primary completion date of 2016-12-23. The study status is completed.

The primary outcome was exhaled carbon monoxide, measured as change from baseline to the last available visit, with a timeframe of 8 weeks after the target quit date. Heaviness of Smoking Index is listed as a secondary outcome. The registry does not describe the enrolled participants’ baseline characteristics, the counseling protocol, or additional operational details of outcome collection.

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

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 Exhaled Carbon Monoxide (CO), measured over 8 weeks after target quit date.

The primary endpoint is change in exhaled carbon monoxide (CO) from baseline to the last available visit. The registry gives the timeframe as 8 weeks after the target quit date and reports the measure in parts per million. Exhaled CO is an objective measure related to recent exposure to cigarette smoke; unlike a participant’s report of smoking, it is obtained by measuring a substance in exhaled breath.

The registry describes the endpoint as a mean, with standard deviation used to describe spread among participants. The posted means are 10.88 for Gemfibrozil and 21.63 for Waitlist; the corresponding standard deviations are 12.63 and 22.04. These are reported as outcome values for the change measure. The record does not state the sign convention used to define change, so the values alone do not establish whether a positive value represents an increase or a decrease from baseline.

Using the last available visit allows an outcome to be recorded when a participant’s assessment is not available at a common scheduled visit, but it can leave participants measured at different times. The registry does not report the actual visit timing for each participant or the method used to handle missing assessments. The endpoint is a measure of CO change, not by itself a complete measure of smoking cessation, cravings, or desire to smoke.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The posted primary outcome is continuous: each participant’s exhaled CO change is represented numerically, and the registry summarizes the arm results with a mean and standard deviation. For this type of outcome, the mean describes the group’s average value. The standard deviation describes how much participant values vary around that average. It is not an estimate of the treatment difference and should not be confused with a standard error or confidence interval.

In general, a comparison of two randomized groups can estimate a difference between their means. An interval around that estimate can indicate the range of values reasonably compatible with the observed data under the analysis assumptions. A p-value, when reported, addresses the compatibility of the data with a specified null hypothesis under a statistical model; it is not a measure of the size or clinical importance of an effect. The registry record does not report a two-arm comparison, confidence interval, or p-value for this continuous endpoint, so none of those inferential interpretations can be made from the posted outcome summaries.

The record reports values missing or not estimable for a two-arm comparison and lists zero analyses. This distinction matters: group-level summaries are present, but the registered results do not include a formal comparison of the arms. No model, test, covariate adjustment, or variance estimator for a primary analysis is described. The statistical plan, including whether a comparison was planned and how it was to be conducted, is not reported in the registry record.

The endpoint uses change from baseline to the last available visit. In general, a change score compares a follow-up measurement with a participant’s baseline measurement. Interpreting the sign requires knowing which subtraction order was used. The record does not state that convention. Last available measurements may also be taken at different times if follow-up varies, and the record does not give participant-level visit timing or explain how missing follow-up values were treated.

In general, missing outcome data can affect a comparison if the likelihood of missingness differs between groups or is related to the unobserved outcome. Analyses can use different assumptions and methods to address missing values, but the registry does not report such a method for this endpoint. It also does not describe an analysis population, such as whether the reported results include everyone as randomized or only participants with an available measurement. Those details cannot be inferred from the arm summaries.

The registry lists a secondary outcome, Heaviness of Smoking Index, but does not post its results in the registry record for this analysis. It reports zero analyses. The number of outcomes and the presence of a secondary outcome do not by themselves reveal how multiple testing was handled. In general, evaluating multiple outcomes or time points can increase the chance of at least one apparently notable result; researchers may address that issue through prespecified outcome hierarchies or statistical adjustment. Neither a multiplicity strategy nor a complete statistical analysis plan is reported in the registry record.

The sample-size assumptions describe planning illustrations based on the observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. In general, such calculations estimate the group size that would be needed to detect a specified effect under stated assumptions. They are planning exercises, not evidence about the probability that this completed trial detected an effect. They are not observed power. The registry does not report the trial’s own sample-size justification or protocol assumptions, and those should not be inferred from an illustration based on observed data.

In general, over-dispersion means that observations vary more than a particular model expects. That concern is relevant when a model assumes a specific distribution or variance structure; ignoring excess variation can make uncertainty estimates too narrow. The posted summaries use means and standard deviations, but the registry does not report a model-based analysis or an over-dispersion assessment. There is therefore no basis for attributing the absence of a comparison to any particular distributional issue.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Gemfibrozil", "Waitlist")
n   <- c(8, 8)
m   <- c(10.88, 21.63)
sp  <- c(12.63, 22.04)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Gemfibrozil  8  10.880  12.630  0.321  21.439
CARM  Waitlist  8  21.630  22.040  3.204  40.056

11. Multiplicity, Missing Data and Analysis Populations

The registry lists Heaviness of Smoking Index as a secondary outcome, in addition to the primary exhaled CO outcome. It reports zero analyses, and no result for the secondary outcome is posted in the registry record. A multiplicity strategy—such as a prespecified testing order or adjustment across outcomes—is not reported. Without that information, the record does not establish how any potential multiple comparisons were to be interpreted.

For the primary endpoint, the registry describes change from baseline to the last available visit. It does not explain how missing baseline or follow-up measurements were handled, whether participants with incomplete measurements were excluded, or whether any imputation or sensitivity analysis was used. The analysis population is also not reported in the registry record. Thus, the posted arm counts should not be treated as proof that every randomized participant contributed an endpoint measurement under a particular analysis rule.

The record gives the primary-outcome values for 8 participants in each arm but says that values were missing or not estimable for a two-arm comparison. It lists zero analyses. The reason the comparison was unavailable is not reported in the registry record. A specific missing-data mechanism or analytic explanation cannot be inferred from that status.

12. 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 5% reporting threshold.

Most frequent non-serious adverse event terms

The adverse-event figures list 8 participants at risk in each arm. The serious adverse event count is 0 in Gemfibrozil and 0 in Waitlist. The registry lists 1 other adverse event in each arm. These are counts as posted; the record does not provide detailed event descriptions or a statistical comparison of safety outcomes.

The deaths fields are null, so deaths are not reported in the registry record. No serious adverse event terms are listed. A zero count in these posted figures means that no serious adverse events are recorded for the listed groups in this result entry; it does not establish that an event could not occur, or describe the precision of any safety comparison. With a small study and no reported inferential safety analysis, these counts are descriptive and should not be treated as a comprehensive assessment of risk.

The registry does not provide further details about event severity beyond the serious versus other categories, timing, attribution, or how events were collected. Those details should not be inferred from the counts alone.

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

The posted data describe a randomized Phase 2 study comparing gemfibrozil plus smoking cessation counseling with counseling and a waitlist comparator. The primary outcome is mean change in exhaled CO from baseline to the last available visit, assessed 8 weeks after the target quit date. The registry reports arm means and standard deviations, but it does not report a two-arm statistical comparison for this outcome.

Accordingly, the record does not provide an estimated treatment contrast with a confidence interval or p-value. The reported means are descriptive, and their interpretation is further limited because the registry does not state the sign convention for the change score. The values do not directly show how many participants quit smoking, and they are not results for cravings or desire to smoke. Heaviness of Smoking Index is listed as a secondary outcome, but its results are not reported in the registry record.

The result entry also does not report a statistical analysis plan, analysis population, missing-data method, or multiplicity procedure. These absences limit the ability to assess how the posted summaries relate to the trial’s intended analyses. The safety entry reports no serious adverse events and one other adverse event in each arm, while deaths are not reported in the registry record. These small descriptive counts do not constitute a comprehensive safety evaluation.

Overall, the registry supports a description of the recorded group summaries and adverse-event counts. It does not provide the inferential evidence needed to quantify the precision of a between-arm effect on the primary endpoint. The absence of a reported comparison should not be taken as evidence of either benefit or lack of benefit; it means that such a conclusion cannot be drawn from the posted analysis.

14. Why This Trial Matters Statistically

This study raises a useful statistical distinction between reporting group summaries and reporting a comparative analysis. Means and standard deviations describe the observed data in each arm, but a clinical trial question generally concerns the difference between groups and the uncertainty around that difference. The registry record includes the former and does not include the latter for the primary outcome.

The endpoint also illustrates why outcome definitions matter. A change score needs a stated direction convention to show what positive and negative values mean. Its timing matters as well: the record defines the endpoint using the last available visit and gives a timeframe of 8 weeks after the target quit date, but does not describe how visit timing varied or how missing measurements were handled. Those details affect how readers understand the estimand and the population represented by the result.

For biostatisticians and clinical researchers, the record is a reminder to distinguish prespecified design features from analyses that are actually posted. Randomized allocation and a completed status do not substitute for a reported treatment contrast, confidence interval, or analysis method. Likewise, planning illustrations based on observed effects are not observed power and do not replace the trial’s own design justification.

Finally, the trial shows why descriptive adverse-event counts should be read within their scope. The registry reports the listed counts, but does not include the detail or precision needed for a broad safety comparison. Careful interpretation depends not only on the numbers present, but also on identifying which questions the registry results do not answer.

15. 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 posted primary endpoint is based on change from baseline to the last available visit, but the registry does not define the direction convention or give the participant-level timing of those visits. It is therefore difficult to interpret the direction and comparability of the reported change values. Missing-data handling and the analysis population are not reported.

The record provides arm-level means and standard deviations but no estimable two-arm comparison, confidence interval, or p-value. The reason that a comparison is missing is not reported in the registry record. The trial is listed as randomized and has 8 participants in each outcome arm, but details of sequence generation and allocation concealment are not reported. Masking is listed as none.

Other trial details relevant to interpretation are not reported in the registry record, including participant characteristics, eligibility criteria, the counseling protocol, and the trial’s statistical analysis plan or sample-size justification. Heaviness of Smoking Index is listed as a secondary outcome, but no result is posted. The registry does not report a multiplicity approach.

The adverse-event entry is limited to counts: no serious adverse events are recorded, and one other adverse event is listed in each arm. Deaths are not reported in the registry record, and event descriptions, timing, attribution, and collection methods are not given. These limitations mean the available registry results support only a narrow descriptive reading, not a comprehensive assessment of efficacy or safety.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Gemfibrozil for Nicotine Smoking Cessation — NCT02638597.
• Registry record last updated 2019-02-01; status last verified 2019-01.
• Results first posted 2019-02-01.
• 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.

19. Record Summary

The registry record describes a completed, randomized, parallel-group Phase 2 trial of gemfibrozil for nicotine smoking cessation. The Gemfibrozil arm received counseling plus gemfibrozil 600 mg twice daily for 9 weeks; the Waitlist arm received counseling without medication during the trial. Masking is listed as none.

The primary outcome was mean change in exhaled CO from baseline to the last available visit, with a timeframe of 8 weeks after the target quit date. Posted means are 10.88 for Gemfibrozil and 21.63 for Waitlist, with standard deviations of 12.63 and 22.04. A two-arm comparison is not reported as estimable, and the registry lists zero analyses. Heaviness of Smoking Index is listed as a secondary outcome without posted results. Serious adverse event counts are 0 in both arms; other adverse event counts are 1 in each arm. Deaths are not reported in the registry record.