The Effectiveness of Smoking Cessation in Prediabetic Smokers: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Effectiveness of Smoking Cessation in Prediabetic Smokers (NCT01926041), a non-randomized na study. The primary outcome is Number of Participants With New-onset Type 2 Diabetes Mellitus (DM).

2. Clinical Question

The study addresses a clinical and public-health question described in its rationale: whether a program that combines smoking cessation support with weight-control coaching is associated with long-term glycemic and diabetes-related outcomes in people with prediabetes who smoke. The rationale notes that existing literature on smoking cessation and new-onset diabetes risk is conflicting. The intervention is designed to address smoking cessation and post-cessation weight gain together, rather than treating either as the sole focus.

The statistical question is narrower than the overall rationale. It concerns the recorded occurrence of new-onset type 2 diabetes under the study’s stated definition and within the stated follow-up horizon. The available record gives the outcome definition and names intention-to-treat as the primary population, but does not report the primary outcome results. Therefore, no group-specific primary event frequency, relative or absolute comparison, uncertainty interval, or test result can be described.

Because participants were not randomized, any reported association would require cautious interpretation even if outcome estimates were available. Non-random allocation can leave the groups different in ways that affect both participation in the program and diabetes risk. The registry record does not describe adjustment methods or provide participant characteristics needed to assess such differences. The comparison is consequently best understood as an observational contrast between intervention and usual-care groups, not as a randomized estimate of the program’s causal effect.

3. Trial Design

The study is registered as a parallel, non-randomized intervention study with no masking. Its title is “The Effectiveness of Smoking Cessation in Prediabetic Smokers,” and its listed sponsor is National Taiwan University Hospital. The registry lists enrollment of 589. The recorded start date is 2013-08-01 and the primary completion date is 2020-12-31; the status is active, not recruiting. The phase is listed as NA.

The intervention arm is described as receiving a 16-week FIT2 program. That program combines smoking cessation therapy with individualized behavioral coaching in diet and physical activity, with the stated aim of restricting post-cessation weight gain. The interventions listed include varenicline for tobacco smoking cessation and individualized counseling about smoking cessation and weight-control techniques. The comparator arm is described as receiving usual care.

The parallel structure means the intervention and usual-care groups are followed as separate arms. However, assignment was non-randomized. The registry explicitly cautions that the arms are not a like-for-like control comparison. Without random assignment, differences in baseline characteristics, clinical circumstances, motivation, access, or other factors may be associated with both group membership and the outcome. The record does not report details of allocation procedures or adjustment methods, so their role cannot be assessed.

The primary outcome is the number of participants with new-onset type 2 diabetes mellitus, assessed up to 5 years. It is defined using repeated fulfillment of at least one of the listed glucose or A1C criteria, or treatment with medications for physician-diagnosed type 2 diabetes. The primary population is labeled intention-to-treat. The record also lists secondary outcomes that include regression to normoglycemia, major adverse cardiac events, chronic kidney disease progression, NAFLD progression, malignancy incidence, all-cause mortality, and HbA1c change between baseline and 6 months.

The registry record does not report a detailed statistical analysis plan, a sample-size justification, interim analyses, or how non-random allocation was addressed analytically. Nor does it give the primary outcome counts or effect estimates. These omissions limit evaluation of both the intended analysis and the results that would be needed to answer the study question.

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

Analysis population for the primary outcome, as defined in the registry: Intention-to-treat analysis

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 New-onset Type 2 Diabetes Mellitus (DM), measured over Up to 5 years.

The primary endpoint is the number of participants with new-onset type 2 diabetes mellitus (DM), with assessment up to 5 years. The registry defines the endpoint as repeated evidence of at least one of several diagnostic criteria: fasting plasma glucose of at least 126 mg/dL (7.0 mmol/L); random plasma glucose of at least 200 mg/dL (11.1 mmol/L) with hyperglycemic symptoms, or the same threshold two hours after a 75-g oral glucose load; A1C of at least 6.5%; or use of medications for physician-diagnosed type 2 DM. The record specifies an intention-to-treat population for this outcome.

Using a defined clinical outcome makes it possible to count participants who meet the study’s stated criteria during follow-up. Repeated fulfillment is part of the recorded definition and distinguishes the endpoint from a single isolated test result. The inclusion of medication for physician-diagnosed type 2 diabetes also means the definition is not based solely on laboratory values.

As a statistical endpoint, this is a binary participant-level outcome summarized as a count: a participant either meets the recorded definition or does not. The registry does not report how many participants in either arm met the definition, the proportion with the outcome, or a comparative estimate. It therefore does not support a numerical conclusion about the observed primary endpoint. The intended follow-up horizon is up to 5 years, but the record does not provide the timing or completeness of individual follow-up.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a participant count represent?

The primary outcome is recorded as a count of participants who meet the definition of new-onset type 2 diabetes. This kind of outcome is often described as binary at the participant level: each participant is classified as meeting or not meeting the endpoint. A count can be informative, but interpretation usually also depends on the number of participants observed in each group and on the duration and completeness of follow-up. The registry record gives an outcome horizon of up to 5 years but does not report the primary event counts or comparative estimates.

For a comparison, analysts may report the event frequency in each group and an effect measure that expresses the difference or relative contrast between groups. A confidence interval communicates the range of effect values reasonably compatible with the data and the analysis assumptions. A narrower interval indicates greater precision than a wider interval. A p-value addresses compatibility with a specified statistical null model; it does not measure the size or clinical importance of an effect. In this registry record, no primary-outcome confidence interval or p-value is reported, so these ideas cannot be applied to a particular diabetes estimate.

Why does non-random allocation matter?

Random assignment is used in clinical trials to make group membership independent, on average, of participant characteristics before treatment. That helps support a causal interpretation of a between-group contrast. Here, allocation is explicitly non-randomized, and the registry warns that the arms are not a like-for-like control comparison. Participants entering the program may differ from those receiving usual care in characteristics that also relate to diabetes risk or follow-up. This can produce confounding: an apparent association between group and outcome may partly represent those pre-existing or concurrent differences.

Adjustment methods can account for measured variables when appropriately selected and implemented. They cannot automatically remove confounding due to variables that were not measured, measured poorly, or handled inadequately. The registry record does not describe baseline adjustment, propensity methods, stratification, or another approach to confounding control. It also does not report participant characteristics by arm. The adjusted nature and credibility of any estimate therefore cannot be evaluated from the record.

What does intention-to-treat mean in this record?

The primary analysis population is described as intention-to-treat. In general, an intention-to-treat approach seeks to analyze participants according to their original study-group assignment, rather than regrouping them according to adherence or later treatment received. This can help preserve the meaning of an assigned-group comparison in randomized trials. Because allocation was non-randomized, the registry label alone does not resolve the comparability issue. The record does not explain how group membership was defined, whether participants who changed exposure remained in their initial group, or how departures from the planned intervention were handled.

The record also does not state how missing outcome data were handled. Missingness matters if participants without observed outcomes differ from those with observed outcomes, particularly if that pattern differs between groups. Complete-case analysis, imputation, and sensitivity analyses make different assumptions; the registry record does not indicate which, if any, were used. Follow-up is stated as up to 5 years, but the record does not report individual observation time, censoring, or loss to follow-up.

How should safety counts be understood?

Adverse-event counts are descriptive summaries of participants recorded with events. The registry lists serious adverse events and deaths separately from other adverse events. A zero serious-event count means none were recorded in the listed group during the reported period; it does not establish that the underlying risk is zero. The counts also do not convey event severity beyond the serious-event category, event timing, recurrence, or the relationship of events to the intervention. Without a specified comparative analysis, raw counts should not be treated as evidence that one arm is safer.

How do planning illustrations differ from trial results?

Sample-size calculations are planning exercises that show how many participants may be needed under stated assumptions to detect an effect with a specified level of statistical power. They are not results, and they are not observed power. The registry’s planning description says the illustrations use a two-sided significance level of 0.05, equal allocation, and a normal approximation, with the effect to detect expressed as a fraction of the observed effect. For time-to-event outcomes, the description refers to total events; for other outcomes, it refers to participants per arm.

These assumptions describe planning illustrations, not necessarily the original trial design. The record does not report a trial-specific sample-size justification or indicate that these assumptions governed enrollment. Because the primary result itself is not reported, a planning illustration based on an observed effect cannot be used to reconstruct the trial’s outcome or infer its precision. It must not be interpreted as evidence that the trial had a particular level of power to detect a true effect.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Intervention (FIT2 Program)", "Usual Care")
n      <- c(279, 310)
events <- c(83, 134)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Intervention (FIT2 Program)  279  83  29.7  24.4  35.5  24.7  35.4  24.7  35.4
ARM  Usual Care  310  134  43.2  37.6  48.9  37.8  48.8  37.8  48.8

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 11 outcome measures and 3 analyses. It names secondary outcomes that include regression to normoglycemia, major adverse cardiac events, chronic kidney disease progression, NAFLD progression, malignancy incidence, all-cause mortality, and HbA1c change between baseline and 6 months. The record does not explain how the listed outcomes relate to the analysis count, which secondary outcomes were tested, or whether any were designated as key secondary outcomes.

When multiple outcomes or analyses are examined, the chance of finding at least one apparently notable result can increase. Statistical approaches such as prespecified outcome hierarchies or adjustments for multiple comparisons can address aspects of this issue, but the registry record does not report a multiplicity strategy. It also does not report which analyses were prespecified, whether any analyses were exploratory, or whether an analysis plan was amended. Thus, no claim about control of multiplicity can be made.

Missing-data methods are likewise not reported in the registry record. The entry identifies an intention-to-treat population for the primary outcome, but does not say how participants with incomplete outcome ascertainment were treated, whether follow-up differed by arm, or whether sensitivity analyses were conducted. The stated outcome horizon is up to 5 years; that does not establish that all participants were followed for the same duration or that outcomes were observed for everyone.

These reporting gaps matter because missingness and selective analysis can affect both the estimated result and the confidence placed in it. The primary outcome counts and estimates are not reported, so it is not possible to assess precision, missing-data impact, or multiplicity in relation to an actual result. The listed analysis population is useful context, but it is not a substitute for a description of the analysis procedures.

12. 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 5% reporting threshold.

Most frequent non-serious adverse event terms

The registry lists serious adverse events, other adverse events, and deaths separately for the intervention and usual-care groups. For the FIT2 intervention group, 0 serious adverse events were recorded among 279 participants at risk, 50 participants were listed with other adverse events among 279 at risk, and 0 deaths were recorded. For usual care, the corresponding entries are 0 serious adverse events among 310 at risk, 65 participants with other adverse events among 310 at risk, and 0 deaths.

These are reported counts, not adjusted comparisons. The registry does not provide a statistical test, confidence interval, event descriptions, timing, duration, or information about whether events were judged related to the intervention. The “other adverse events” category should not be read as a specific diagnosis or as an assessment of severity beyond the distinction from serious adverse events. The figures also do not show whether any participant experienced more than one event.

Zero recorded serious adverse events or deaths does not prove that such events could not occur; it means none are listed for the reported groups. Differences in the other-adverse-event counts should not be interpreted as a causal safety difference because allocation was non-randomized and the groups are not a like-for-like control comparison. The record does not describe how adverse events were collected or whether reporting was complete.

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

The registry record establishes that the study examined a combined smoking-cessation and weight-control program for prediabetic smokers, compared with usual care. It identifies the intervention as a 16-week FIT2 program and sets new-onset type 2 diabetes as the primary outcome, assessed up to 5 years. The endpoint definition includes repeated glucose or A1C criteria, or medication for physician-diagnosed type 2 diabetes.

Those design details do not answer whether the program was associated with a different diabetes outcome. The registry record does not report primary event counts, a between-group effect estimate, a confidence interval, or a p-value. It therefore cannot show the direction, magnitude, or precision of the primary result. Nor can the absence of those results be interpreted as a finding of no effect; it is a lack of a reported result in this record.

Even if a comparative result were available, its interpretation would need to account for non-random allocation. The registry specifically notes that the arms are not a like-for-like comparison. Differences in participant characteristics or other factors could influence both group membership and diabetes outcomes. The record does not report the methods used to address such differences, so a causal interpretation cannot be assessed.

The listed safety counts describe events recorded in each arm, but they are not a causal safety comparison. They do not provide details about event type, timing, or attribution. Similarly, the secondary outcome list indicates what outcomes were included in the registry, not that results for each outcome are reported or that a particular pattern was observed.

Accordingly, the record supports a description of the study question, intervention, comparison, primary endpoint, and some adverse-event counts. It does not support a conclusion that FIT2 increases, reduces, or has no association with new-onset type 2 diabetes. The results needed to answer that question are not reported in the registry record.

14. Why This Trial Matters Statistically

This trial is statistically noteworthy because its question combines a behavioral program, smoking cessation therapy, weight control, and a long-term glycemic outcome. The intervention description makes clear that the program targets smoking cessation and post-cessation weight gain together. The primary endpoint then focuses on new-onset type 2 diabetes in a population described as prediabetic smokers. That combination makes the study question relevant to how an intervention package is evaluated, rather than isolating the effect of one component.

The non-randomized allocation is central to the interpretation. A parallel comparison can describe outcomes across arms, but group membership is not exchangeable merely because one arm received FIT2 and the other usual care. The registry itself cautions that the arms are not a like-for-like control comparison. Any statistical comparison would therefore need to address confounding, and readers would need enough information about participant characteristics and analytic methods to judge what has been addressed. That information is not reported in the record.

Outcome definition also matters. The primary endpoint uses repeated fulfillment of diagnostic criteria or treatment for physician-diagnosed type 2 diabetes, rather than a single laboratory result alone. The registry specifies an intention-to-treat population and an assessment horizon of up to 5 years. These details tell readers what the study intended to count, but not how completely outcomes were observed or how participants with missing information were handled.

Finally, the record illustrates why methods and results need to be read together. It lists a primary question, secondary outcomes, and adverse-event counts, but does not report the primary effect estimate or its precision. Without the outcome results and the analysis details, the statistical evidence for the central question cannot be evaluated. The distinction between a well-defined research question and a reported answer is especially important in non-randomized studies.

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 principal limitation in interpreting this study record is the absence of reported primary outcome results. There are no event counts for new-onset type 2 diabetes by arm, no effect estimate, and no uncertainty interval or test result. As a result, the direction and precision of the primary comparison cannot be assessed. This is a limitation of what the registry record reports, not evidence that an effect was absent.

Non-random allocation limits causal interpretation. The registry warns that the arms are not a like-for-like control comparison, and it does not describe the allocation process or methods used to address confounding. It also does not provide baseline characteristics by arm. Thus, readers cannot judge the extent of observed group differences or whether statistical adjustment was adequate.

The record gives the primary outcome horizon as up to 5 years but does not report participant-level follow-up, loss to follow-up, censoring, or outcome ascertainment completeness. Missing-data handling and sensitivity analyses are not reported. These gaps matter for an outcome measured over time, because incomplete observation could affect the apparent number of participants meeting the endpoint.

The registry lists multiple outcomes and analyses but does not explain the analysis plan, multiplicity approach, or which analyses were prespecified. It also does not report a trial-specific sample-size justification or interim analyses. The adverse-event entry gives aggregate counts without event details, collection procedures, or attribution. These limitations prevent a full assessment of outcome quality, analysis choices, and safety interpretation.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: The Effectiveness of Smoking Cessation in Prediabetic Smokers — NCT01926041.
• Registry record last updated 2026-07-24; status last verified 2026-07.
• Results first posted 2023-02-22.
• 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 parallel, non-randomized study of a 16-week FIT2 program versus usual care among prediabetic smokers. The program combines smoking cessation therapy with individualized coaching in diet and physical activity. The registry lists enrollment of 589, sponsor National Taiwan University Hospital, start date 2013-08-01, primary completion date 2020-12-31, and status active, not recruiting.

The primary outcome is new-onset type 2 diabetes assessed up to 5 years, using repeated diagnostic criteria or medication for physician-diagnosed diabetes. The primary population is described as intention-to-treat. The primary outcome counts and comparative results are not reported in the registry record.

The adverse-event entry lists zero serious adverse events and zero deaths in both arms, alongside other adverse-event counts of 50 among 279 at risk in the intervention group and 65 among 310 at risk in usual care. Because allocation was non-randomized, these figures do not establish causal differences between groups. Details of the statistical analysis plan, missing-data methods, multiplicity handling, and confounding adjustment are not reported.