Web-based Smoking Cessation Program for Tribal College Students: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Web-based Smoking Cessation Program for Tribal College Students (NCT02050308), a randomized phase 3 study. The primary outcome is Number of Participants With 7-day Point Prevalence Abstinence.

2. Clinical Question

The clinical question is whether the recorded proportion achieving this specific abstinence outcome differed between participants assigned to I-ANBL and those assigned to Honoring the Gift of Heart Health. The registry record identifies random allocation, but does not report detailed eligibility criteria, allocation procedures, or the statistical plan for the primary comparison. It also does not report whether all enrolled participants completed follow-up or how missing outcome measurements were handled. Those details matter when interpreting the observed group counts: the posted results describe recorded outcomes, while the degree to which they represent outcomes for all randomized participants is not reported in the registry record.

3. Trial Design

The registry record describes a completed, randomized, parallel-group phase 3 study with no masking. Enrollment was 251. The two groups were assigned to I-ANBL or Honoring the Gift of Heart Health. The study’s stated purpose was to test a culturally tailored Internet-based program intended to help American Indian tribal college students quit smoking. The registry record does not report the exact randomization procedure, whether assignment was concealed, or the original statistical design assumptions.

I-ANBL was described as having 9 individual Internet sessions across a 12 week period, followed by an additional individual Internet session at 6 months. The sessions were described as lasting about half-an-hour and discussing topics important to quitting smoking. The comparator was also described as a culturally tailored Internet program, with sessions addressing heart health. The description of that program is incomplete in the registry record, so its full content and how closely the session schedules matched cannot be established from the record.

The registry record lists nicotine gum, patch, or lozenge, as well as Zyban® or Chantix®, among the interventions. It does not establish from the posted outcome information whether these were available in both groups, used by particular participants, or managed as part of the program comparison. Their role should therefore not be assumed when interpreting the group contrast.

The primary outcome was assessed at 6 months. It counted participants with self-reported and salivary-cotinine-verified 7-day point prevalence abstinence. Three secondary outcomes were posted: cigarettes per day, number of quit attempts, and participation in all sessions over the course of 6 months. The registry record does not report a prespecified analysis population, handling of protocol deviations, follow-up completion rates, or the trial’s original sample-size justification. Randomization supports a between-group comparison in principle, but the reporting gaps limit assessment of how the analysis was carried out.

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 Number of Participants With 7-day Point Prevalence Abstinence, measured over 6 months.

The primary endpoint counts participants who met the study’s definition of 7-day point prevalence abstinence at the 6-month follow-up. To qualify, a participant had to report no smoking during the previous 7 days and have abstinence verified biochemically using salivary cotinine. The endpoint is a count, with each participant classified according to whether the criterion was met.

This type of endpoint is used to make a group-level comparison of abstinence status at a specified follow-up. Requiring both self-report and biochemical verification gives the endpoint two sources of information about the same short-window status. It does not, however, measure continuous abstinence throughout the period since enrollment. A participant could meet the 7-day definition without having been abstinent throughout the preceding months; the registry’s stated definition is limited to the previous 7 days.

At the primary follow-up, 9 participants were recorded as meeting the endpoint in each group. The group sizes were 127 for Honoring the Gift of Heart Health and 124 for I-ANBL. The endpoint is clinically interpretable as a count of participants meeting the specified status, but its interpretation depends on complete and comparable ascertainment in both groups. The registry record does not report missing-data handling, the number of participants assessed at follow-up, or how unverified or unavailable measurements were classified. Those details are important for understanding whether the posted counts represent all randomized participants or only those with an observed outcome.

7. Results Posted in the Registry

• Internet-All Nations Breath of Life (I-ANBL): 7.3% (9/124) versus 7.1% (9/127) on control; risk difference 0.2 percentage points (95% CI -6.2 to 6.6), risk ratio 1.02 (0.42–2.49); unadjusted two-proportion z-test p = 0.958.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Cigarettes Per Day

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Honoring the Gift of Heart Health: mean 5.43 versus 4.00 on control; difference 1.43 (95% CI 0.12 to 2.74), standardized effect d = 0.27; z-test p = 0.032.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically higher for Honoring the Gift of Heart Health than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The secondary outcomes broaden the description beyond abstinence at follow-up: they include cigarettes smoked daily, quit attempts, and participation in all sessions over the course of 6 months. The posted information does not provide numerical results for every listed secondary measure. As a result, an overall pattern across all secondary outcomes cannot be established from the registry record.

The cigarettes-per-day comparison has a nominal unadjusted result that differs from the primary outcome’s statistical pattern. It should not be taken as confirmation of the primary endpoint or as an overall demonstration that one program performed better. The outcomes measure different behaviors, and the primary endpoint remains the central comparison identified in the record. In addition, the secondary arm labels appear reversed relative to the primary arm descriptions, so the direction and group attribution require caution.

Unadjusted secondary results carry less weight when several outcomes are examined because the chance of finding an apparently notable result can increase across multiple comparisons. The registry record does not report a multiplicity procedure or a prespecified hierarchy for these outcomes. This does not make secondary measures uninformative, but it means that an isolated p-value should be treated as exploratory and interpreted with the full set of outcomes and the analysis plan in mind.

The record lists three secondary outcomes and four outcome measures overall, but does not post results for quit attempts or session participation. It also does not report whether the secondary analyses were prespecified, adjusted for baseline measurements, or based on the same analysis population as the primary endpoint. These gaps prevent a complete account of whether the secondary findings are consistent with one another or with the primary comparison.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Cigarettes Per Day
• Number of Quit Attempts
• Number of Participants Who Participated in All Sessions Over the Course of 6 Months.

9. Statistical Interpretation

10. Statistical Methods Explained

Randomization is a design approach intended to make groups comparable, on average, with respect to factors that may affect an outcome. In a randomized comparison, differences in outcome can be assessed between assigned groups without relying solely on measured baseline characteristics. The registry record identifies the trial as randomized and parallel-group, but does not report the allocation sequence method, concealment procedures, or whether analyses followed initial assignment regardless of participation. Those details are not reported in the registry record.

What does the primary effect estimate represent?

The primary comparison is expressed as a risk difference: the difference between the groups’ proportions meeting the abstinence definition. A risk difference near zero means that the observed proportions are similar. A positive or negative value indicates which group has the larger observed proportion, depending on the order used to define the contrast. The estimate posted for this trial is very close to zero. Its confidence interval includes zero, so the data are compatible with no difference as well as with differences in either direction.

Other effect measures can express the same binary-outcome comparison in different ways. A risk ratio compares the groups’ event proportions as a ratio, while an odds ratio compares their odds. These measures do not have the same interpretation or scale as a risk difference. Their confidence intervals also include the value corresponding to no association. For this trial, they do not change the broad reading of the primary comparison: the observed group outcomes are similar, while the estimates remain uncertain.

How should a p-value be read?

A p-value describes how unusual data at least as incompatible with a specified null model would be if that model and the analysis assumptions were correct. It is not the probability that the null hypothesis is true, and it does not measure the size or clinical importance of a difference. The primary unadjusted p-value is 0.958, which is not evidence against the null model in this comparison. The p-value does not demonstrate equivalence or prove that the programs have the same effect.

The secondary cigarettes-per-day comparison has an unadjusted p-value of 0.032. A result below a conventional threshold may attract attention, but interpretation depends on whether the comparison was prespecified, how many outcomes were examined, and what analysis plan was followed. The registry record does not report a multiplicity adjustment or the trial’s analysis plan. The secondary result should therefore be treated as exploratory rather than as a definitive finding.

What does a confidence interval add?

A confidence interval describes the range of effect estimates reasonably compatible with the observed data under the statistical model and its assumptions. It communicates precision as well as direction. For the primary endpoint, the interval crosses zero, indicating that the posted data do not resolve whether the group difference is positive or negative. The estimate being close to zero does not make the interval unimportant: its span indicates that meaningfully different underlying effects may remain compatible with the data.

For the cigarettes-per-day comparison, the posted interval lies on one side of zero. That is consistent with the unadjusted p-value for that comparison. But the interval does not account for the uncertainty introduced by selecting among several outcome comparisons unless the analysis explicitly incorporates multiplicity. Nor does it resolve the apparent mismatch in secondary arm labels.

Why does the endpoint definition matter?

The primary endpoint combines self-report and salivary cotinine verification and applies a 7-day abstinence window at the 6-month follow-up. The result is therefore a point-prevalence measure at one follow-up, rather than a measure of abstinence maintained continuously. A count endpoint is straightforward to understand, but its reliability depends on who was assessed, whether verification was obtained, and how unavailable measurements were treated. Those operational details are not reported in the registry record.

The registry record also does not report covariate adjustment, subgroup analyses, interim analyses, or a prespecified statistical plan. The posted comparison statistics can describe the observed contrast, but they cannot establish what methods were planned before the outcomes were examined. In general, prespecified methods help distinguish confirmatory analyses from analyses selected after results are known. The record does not give enough information to assess that distinction for this trial.

11. Confidence Intervals and Precision

Precision concerns how much uncertainty surrounds an estimated effect. The primary risk-difference confidence interval extends across zero, so it is compatible with the possibility of a difference favoring either group as well as no difference. The point estimate is very close to zero, but the interval is the more informative guide to how much the data constrain the underlying comparison. It does not support a conclusion that the groups are identical.

The primary comparison is based on 9 participants meeting the endpoint in each group, with group sizes of 127 and 124. With relatively few recorded endpoint events, estimates for a binary outcome can be imprecise even when the total number enrolled is larger. The confidence interval reflects this uncertainty. Its width should be considered alongside the point estimate and the endpoint definition, rather than treating the p-value alone as a measure of certainty.

The posted risk-ratio and odds-ratio intervals likewise include their respective no-association values. Different effect measures can look different numerically because they use different scales; they do not remove the uncertainty in the underlying data. The registry record does not report adjusted confidence intervals or additional analyses that might address differences in participant characteristics or missing outcomes.

The cigarettes-per-day interval is narrower in the sense that it excludes zero, but that result is unadjusted and belongs to a secondary outcome. Its apparent arm-label inconsistency also complicates interpretation. Precision in a statistical interval does not correct possible labeling problems, selection among multiple outcomes, or incomplete reporting. The registry record does not report enough information to assess those issues fully.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are illustrations based on the observed effect, not the trial’s original design justification. For the primary binary outcome, the estimates are participants per arm. The stated assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The calculation uses the stated fraction of the observed effect as the effect to detect. The trial’s own original sample-size assumptions are not reported in the registry record.

For planning at 100% of the observed effect, the illustration gives 355,548 participants per arm for 80% power and 475,977 participants per arm for 90% power. At 75% of the observed effect, the corresponding figures are 630,343 and 843,850 participants per arm. At 50% of the observed effect, they are 1,414,348 and 1,893,410 participants per arm.

In plain language, the 80% power column represents the number of participants per arm that the stated calculation estimates would be needed to detect the selected effect with 80% power under its assumptions. The 90% power column uses a higher target probability of detecting that effect, again under the stated assumptions. Detecting a smaller effect requires more participants, which is why the planning figures increase as the effect fraction decreases.

These figures are not observed power. They are planning illustrations generated from the observed effect and should not be read as a retrospective measure of the trial’s success or as the original enrollment target. Because the observed primary effect is very close to zero, the resulting required sample estimates are very large. The registry record does not report the trial’s original sample-size justification, so these illustrations cannot be used to infer what enrollment target investigators intended before the study began.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.071; treatment proportion p₁ = 0.073; average p̄ = 0.072.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.3649 = 0.7152.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.3649 = 0.3071.
4. n = (0.7152 + 0.3071)² / (0.0017)² = 355,547.6, rounded up to 355,548 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
p0 <- 0.0708661417322835                          # control proportion
p1 <- 0.0725806451612903                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(2050308)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 355,548 (80% power), 475,977 (90% power)
 75% of observed effect: n per arm = 630,343 (80% power), 843,850 (90% power)
 50% of observed effect: n per arm = 1,414,348 (80% power), 1,893,410 (90% power)
power.prop.test: 355547.6 
Simulated power at n = 355,548 per arm: 0.799 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

Multiplicity arises when several outcomes, comparisons, subgroups, or analyses are considered. Even when each comparison is evaluated using the same statistical threshold, the chance of at least one apparently notable finding can increase as more comparisons are made. A prespecified hierarchy or adjustment procedure can help control that issue, but the registry record does not report such a procedure for this trial.

The record identifies one primary endpoint and lists three secondary outcomes. It also reports no entries under reported analyses. This absence does not establish that no analyses were performed; it means the registry record does not report a formal analysis entry or enough detail to determine the planned analysis strategy. The posted outcome summaries and comparisons do not substitute for a documented statistical analysis plan.

Missing-data handling is also not reported in the registry record. There is no posted account of how participants without a 6-month measurement were handled, whether biochemical verification was unavailable for any participants, or whether missing outcomes were classified as smoking, excluded, or handled through another method. The number assessed at follow-up and the reasons for any missing data are not reported. Without these details, it is not possible to assess the potential influence of incomplete outcome ascertainment.

The analysis population is not reported. The record does not state whether the primary comparison followed an intention-to-treat approach, included only participants who completed treatment, or used another rule. It also does not report how protocol deviations or use of other cessation aids were handled. These issues matter because excluding participants or analyzing them according to treatment received can weaken the balance created by random assignment.

Consequently, the primary comparison can be read as the posted group-level result, but its analysis assumptions and robustness cannot be fully evaluated. The secondary unadjusted result deserves particular restraint because multiplicity procedures and analysis populations are not reported. These limitations concern the documentation available in the registry record; they do not establish what procedures investigators may have used outside the record.

15. 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.

The serious adverse event figures report zero affected participants in each group: 127 participants were listed at risk in Honoring the Gift of Heart Health, and 124 in I-ANBL. The record also lists zero deaths in each group. No serious adverse event terms appear among the posted terms.

These figures describe what was recorded in the registry record; they do not establish that no adverse experiences of any kind occurred. The record reports zero serious adverse events, but does not provide event-level details, follow-up duration for safety, or an account of how events were collected and classified. The non-serious adverse event counts are also listed as zero for both groups, but the registry provides no further detail about ascertainment or reporting procedures.

Accordingly, the safety figures should be read narrowly as registry-reported counts, not as a comprehensive evaluation of safety or as proof of absence of risk. The registry record does not report whether adverse event collection was systematic across all participants or whether any events were missing from the record.

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

The primary result describes the number of participants meeting a specific abstinence definition at a specific follow-up. Both groups had 9 recorded participants meeting the endpoint, and the estimated difference was very close to zero. The confidence interval includes no difference and extends in both directions. The data therefore do not distinguish the groups on the posted primary comparison, but they also do not establish equivalence or rule out potentially meaningful differences.

The endpoint was 7-day point prevalence abstinence at 6 months, verified by self-report and salivary cotinine. It does not establish continuous abstinence since enrollment, long-term maintenance, or outcomes beyond the follow-up described in the record. Any interpretation should remain tied to that definition.

The record describes a comparison between two culturally tailored Internet programs. It does not describe a comparison against no intervention, and it does not establish how additional cessation aids listed among the interventions were used. The observed comparison should not be generalized to different programs, settings, or populations without evidence beyond this record.

The secondary cigarettes-per-day result is an unadjusted finding and should not override the primary result. The other listed secondary outcomes lack posted numerical results, and the arm labels for the cigarettes-per-day summaries appear inconsistent with the primary arm descriptions. The registry record also does not report the analysis plan, missing-data methods, or multiplicity handling. Together, these reporting limits constrain how strongly the secondary evidence can be interpreted.

These results are statistical descriptions, not medical advice. They do not determine which program an individual should use, and they do not establish that either program does or does not work. They indicate what the registry record reports for this trial’s defined outcomes and the uncertainty around the group comparison.

17. Why This Trial Matters Statistically

This trial raises several useful statistical questions for clinical and behavioral research. Its primary outcome is binary and based on a relatively small number of recorded abstinence events compared with the group sizes. That makes the confidence interval especially important: a point estimate near zero can coexist with considerable uncertainty about the underlying difference.

The comparison also illustrates why a non-significant result should not be confused with evidence of equivalence. The primary p-value is 0.958, and the confidence interval includes zero, but the interval also spans effects in either direction. Without a prespecified equivalence margin and an analysis designed to assess equivalence, the record does not support a claim that the programs have the same outcome.

The secondary outcome provides a contrasting example of why multiplicity and reporting matter. A nominal unadjusted finding can appear notable among several outcomes, yet the record does not document adjustment or a hierarchy for testing. An apparent inconsistency in the secondary arm labels further shows that clear outcome labeling is essential to interpreting even familiar statistics such as a mean difference and confidence interval.

Finally, the planning illustrations make clear that sample-size calculations depend on the effect chosen for detection. Smaller target effects require larger samples under the stated assumptions. These illustrations are based on the observed effect and are not the study’s original design rationale. Separating planning calculations from observed results, and reporting missing-data and analysis-population decisions, are important for transparent interpretation.

18. 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 leaves several trial-specific questions unresolved. It does not report detailed participant eligibility criteria, baseline characteristics, recruitment and follow-up completion, or how many participants had outcome measurements available at 6 months. These omissions make it difficult to assess representativeness and the extent of missing outcome data.

The record does not report the original sample-size justification, allocation method, allocation concealment, statistical analysis plan, or analysis population. Missing-data procedures, interim analyses, covariate adjustment, and protocol-deviation handling are also not reported. Their absence from the registry record prevents assessment of whether the posted results follow prespecified procedures.

The intervention descriptions are incomplete. The record identifies the content and schedule of I-ANBL in part and describes the comparator as a culturally tailored heart-health program, but does not give the comparator’s full program details. Although cessation medications and nicotine replacement products are listed, their use in the groups is not described in the posted outcome information.

The secondary outcome arm labels appear reversed relative to the primary arm descriptions. This creates uncertainty about the attribution and direction of the cigarettes-per-day comparison and should be resolved against the registry record or other authoritative trial documentation before drawing a substantive conclusion from that result.

Finally, numerical results are not posted for the listed quit-attempt and session-participation outcomes. The primary endpoint is limited to 7-day abstinence at the 6-month follow-up, and safety figures are reported as counts without event-level detail. These limitations restrict interpretation to the outcomes and information recorded, rather than allowing a complete assessment of trial conduct or longer-term results.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Web-based Smoking Cessation Program for Tribal College Students — NCT02050308.
• Registry record last updated 2021-12-07; status last verified 2021-11.
• Results first posted 2019-08-06.
• 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.

22. Record Summary

The registry record describes a completed, randomized, parallel-group phase 3 trial with no masking and enrollment of 251. It compared Internet-All Nations Breath of Life with Honoring the Gift of Heart Health among a study population described as American Indian tribal college students.

The primary endpoint was self-reported and salivary-cotinine-verified 7-day point prevalence abstinence at 6 months. Each group had 9 participants recorded as meeting the endpoint. The estimated risk difference was close to zero, its confidence interval included zero, and the unadjusted p-value was 0.958. The record lists three secondary outcomes, but numerical results are not posted for all of them. It reports zero serious adverse events and zero deaths in both groups.

The registry record does not report the original sample-size justification, statistical analysis plan, analysis population, missing-data methods, or multiplicity procedures. An apparent inconsistency in secondary arm labels further limits interpretation of the cigarettes-per-day comparison.