Assessing the Effectiveness of a Pharmacist-delivered Smoking Cessation Program in the State of Qatar: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Assessing the Effectiveness of a Pharmacist-delivered Smoking Cessation Program in the State of Qatar (NCT02123329), a randomized na study. The primary outcome is Self-reported 7-day Point Prevalence Abstinence.

2. Clinical Question

3. Trial Design

The registry describes a completed, randomized, double-masked, parallel-group trial sponsored by Qatar University. Enrollment is listed as 314. The study took place at 8 ambulatory pharmacies in Qatar, according to the brief summary. The record lists the phase as NA. The trial began in 2013-02, with primary completion in 2015-12.

The intervention was a structured program delivered face to face by a pharmacist. Its arm description specifies four sessions at the pharmacy, scheduled at two-to-four-week intervals over eight weeks. The control arm received 5-10 minutes of unstructured brief advice and educational materials. Nicotine replacement therapy was offered in the control description; the intervention description says it was used alongside the program. The brief summary says both groups would be offered nicotine therapy if feasible. The registry does not explain how feasibility was determined.

The masking label is double, but the registry record does not report which people were masked or how masking was maintained. It also does not report details of allocation concealment or the randomization procedure. These omissions limit assessment of those design features from the record alone. The posted primary outcome is self-reported 7-day point prevalence abstinence at 3 months. Separately, the brief summary describes an intended primary outcome confirmed by exhaled carbon monoxide at 12 months. The registry record does not reconcile this difference in measure and timeframe.

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.

3 Month Outcome Measure

6 Month Outcome Measure

12 Month Outcome Measure

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 Self-reported 7-day Point Prevalence Abstinence, measured over 3 months.

The posted primary endpoint is self-reported 7-day point prevalence abstinence, measured as a count of participants. A participant meets the stated definition by reporting that they smoked no cigarettes during the previous 7 days. The outcome timeframe is 3 months. The posted counts are 26 in the control arm and 31 in the intervention arm, with denominators of 98 and 101, respectively.

As a binary outcome, the measure classifies each participant according to whether the stated recent-abstinence definition is met. Counting participants who meet the definition gives a direct summary of how many in each arm reported recent abstinence. The measure captures a short, specified period of smoking behavior at follow-up; it does not by itself describe abstinence over the entire period since enrollment.

The brief summary describes a different planned measure: smoking cessation confirmed by an exhaled carbon monoxide test at 12 months. The posted primary-outcome record instead names self-report at 3 months. The registry record does not explain whether the measure or timeframe changed, or how the two descriptions relate. Interpretation should therefore stay anchored to the outcome as actually posted: self-reported abstinence at 3 months.

7. Results Posted in the Registry

• Intervention Arm: 30.7% (31/101) versus 26.5% (26/98) on control; risk difference 4.2 percentage points (95% CI -8.4 to 16.7), risk ratio 1.16 (0.74–1.80); unadjusted two-proportion z-test p = 0.516.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is recorded as a count of participants meeting a binary definition. For each arm, the registry reports a count and a denominator. The comparison is expressed as a risk difference, and the record also lists a risk ratio and an odds ratio. These are alternative ways to describe the contrast between the arms; each has a different scale and interpretation.

What does the risk difference describe?

In general, a risk difference subtracts the outcome proportion in one group from the outcome proportion in the other. A value of zero represents no difference on this scale. Positive or negative values indicate the direction of the contrast according to the stated arm ordering. The posted estimate is 0.042 for intervention versus control. Its confidence interval ranges from -0.084 to 0.167, crossing zero. That range indicates that the data are compatible with differences on either side of no difference, while also allowing a positive difference larger than the point estimate.

How do the relative measures differ?

In general, a risk ratio compares the outcome proportions by division; a value of one represents equal proportions. An odds ratio compares the odds of the outcome between groups, also with one as its no-difference value. Their interpretation depends on the outcome and the scale, and an odds ratio should not be read as though it were a risk difference. The posted risk ratio is 1.157, with a confidence interval from 0.744 to 1.798. The posted odds ratio is 1.226, with a confidence interval from 0.662 to 2.271. Both intervals include one, so neither relative measure excludes no difference within its reported interval.

What does the p-value say?

In general, a p-value summarizes how unusual data at least as discrepant as those observed would be under a specified null model and its assumptions. It is not the probability that the null model is true, and it does not measure the probability that a result will replicate. The posted unadjusted p-value is 0.516. The registry record does not identify the test, its assumptions, or any adjustment used in obtaining that value. The p-value should therefore be read as a reported unadjusted result rather than as a fully documented analysis procedure.

What does a confidence interval contribute?

In general, a confidence interval conveys the uncertainty around an estimate under a statistical procedure. It gives a range of values compatible with the data and that procedure; it is not a guarantee that the true effect lies within the particular interval. Here, the risk-difference interval includes negative and positive values. The relative-measure intervals include their no-difference value. These features communicate uncertainty that cannot be conveyed by the point estimates alone.

What analysis details are absent?

The registry reports 11 outcome measures and one posted secondary outcome, Health Related Quality of Life. It lists zero posted analysis records. No inferential test, confidence-interval method, covariate-adjustment strategy, missing-data method, or analysis-population definition is reported in the registry record. The record also does not say whether the posted comparison follows the original analysis plan or whether any outcomes or analyses were changed. Those details matter when evaluating how the estimates were produced and how broadly they can be interpreted.

For a binary outcome, the analysis can be sensitive to which participants contribute data and how unavailable outcomes are handled. In general, excluding participants with missing outcome information can affect the comparison if missingness differs between arms or is related to outcome status. The registry does not report missing outcome counts or the handling approach, so the impact of missing data cannot be assessed from this record. This is a limitation of the available statistical documentation, not evidence that a particular handling choice was made.

10. Confidence Intervals and Precision

The risk-difference estimate is 0.042, and its confidence interval runs from -0.084 to 0.167. The interval crosses zero, the no-difference value for this measure. It therefore leaves room for a difference favoring either arm. Its breadth also means that the point estimate should not be treated as a precise estimate of the underlying group contrast.

The risk-ratio estimate is 1.157, with an interval from 0.744 to 1.798. The odds-ratio estimate is 1.226, with an interval from 0.662 to 2.271. For both relative measures, the interval crosses one, their no-difference value. The point estimates lean toward higher abstinence in the intervention arm, but the intervals allow relative effects in the other direction as well.

Confidence intervals describe uncertainty under the methods used to calculate them. The registry record does not report those methods, so the assumptions behind the interval estimates cannot be checked from the posted information. The intervals do not establish that the true effect is equally likely to be any value within their bounds, and they do not resolve the difference between the 3-month self-reported outcome and the 12-month carbon-monoxide-confirmed outcome described in the brief summary.

Overall, the posted estimates are not highly precise about the direction or magnitude of the group difference. The confidence intervals are more informative than the point estimates alone because they show that results compatible with the data include both no difference and effects in either direction.

11. 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 participants per arm, not total events. They are illustrations based on the observed effect, rather than the trial's original design assumptions. The listed assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set as a stated fraction of the observed effect. The registry record does not report the trial's own original sample-size assumptions or justification.

For planning for 100% of the observed effect, the figures are 1,850 participants per arm for 80% power and 2,476 participants per arm for 90% power. For planning for 75% of the observed effect, they are 3,253 participants per arm for 80% power and 4,354 participants per arm for 90% power. For planning for 50% of the observed effect, they are 7,236 participants per arm for 80% power and 9,687 participants per arm for 90% power.

In general, the 80% and 90% power columns describe the planned chance of detecting the specified effect under the stated assumptions if that effect were present. The higher power target requires more participants per arm for each effect fraction. Smaller effects also require more participants per arm to detect, which is why the figures increase as the assumed fraction of the observed effect becomes smaller. These are planning illustrations, not observed power; they do not measure the probability that this completed trial detected an effect.

12. 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 = 0.265; treatment proportion p₁ = 0.307; average p̄ = 0.286.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.6391 = 1.2527.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.6385 = 0.5373.
4. n = (1.2527 + 0.5373)² / (0.0416)² = 1,849.4, rounded up to 1,850 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 <- 0.26530612244898                          # control proportion
p1 <- 0.306930693069307                          # 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(2123329)
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 = 1,850 (80% power), 2,476 (90% power)
 75% of observed effect: n per arm = 3,253 (80% power), 4,354 (90% power)
 50% of observed effect: n per arm = 7,236 (80% power), 9,687 (90% power)
power.prop.test: 1849.4 
Simulated power at n = 1,850 per arm: 0.801 (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.

13. Multiplicity, Missing Data and Analysis Populations

The registry lists 11 outcome measures and identifies Health Related Quality of Life as a secondary outcome. It reports zero posted analysis records. The record does not describe a prespecified hierarchy among outcomes, identify a primary inferential test beyond naming the primary outcome, or report an adjustment for multiple comparisons. It is therefore not possible to determine from the registry record whether multiplicity was addressed in the analysis or how the primary result was selected and interpreted alongside other outcomes.

Multiplicity matters when several outcomes or analyses are considered because repeated testing can increase the chance of a seemingly notable result arising by chance. This is a general statistical concern, not evidence that such an effect occurred in this trial. The registry record does not provide enough analysis detail to assess the issue for the posted results.

Missing-data handling is also not reported in the registry record. The primary-outcome denominators are 98 in the control arm and 101 in the intervention arm, while enrollment is listed as 314. The record does not explain the relationship between these figures, report missing primary outcomes, or describe how missing values were treated. It would be inappropriate to infer a reason for the denominator differences from the posted data alone.

The analysis populations are not reported in the registry record. It does not state whether the primary comparison was based on all randomized participants, participants with observed outcomes, or another defined population. The record also does not describe exclusions after randomization or departures from assigned intervention. Without these details, the analysis cannot be classified confidently as intention-to-treat, per-protocol, or another approach.

These omissions restrict reproducibility and make it harder to assess how robust the comparison is to analytic choices. They do not establish that any specific choice was inappropriate; they mean that the relevant information is not reported in the registry record.

14. 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 non-serious adverse event terms

The adverse-event record lists zero serious adverse events in the control arm and zero in the intervention arm. It also lists zero deaths in each arm. For other adverse events, the record lists zero in the control arm and two in the intervention arm. No serious adverse event terms are listed.

The adverse-event risk sets are listed as 147 for the control arm and 167 for the intervention arm. These figures differ from the denominators in the posted primary outcome record. The registry record does not explain the different counts or describe the period and procedures used to collect adverse events. They should not be treated as interchangeable denominators.

These entries describe the events recorded in the registry; they do not establish whether events were caused by an intervention, whether all events were captured, or whether the groups had equivalent safety experience. The record does not provide event descriptions for the two other adverse events or further detail on severity, timing, or attribution. The counts should therefore be read as registry entries, not as a complete account of safety.

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

The posted primary-outcome comparison shows more participants meeting the self-reported 7-day abstinence definition in the intervention arm than in the control arm, based on the listed counts of 31 of 101 and 26 of 98. The reported risk-difference estimate is 0.042. Its confidence interval includes values below and above zero, and the unadjusted p-value is 0.516. The relative-measure intervals also include their no-difference values. Taken together, these results leave substantial uncertainty about the direction and magnitude of the group contrast.

This finding applies to the outcome as recorded: self-reported abstinence during the previous 7 days at 3 months. It does not directly establish sustained abstinence over a longer period. The brief summary describes carbon-monoxide-confirmed cessation at 12 months, but the registry record does not reconcile that description with the posted primary outcome. The result should not be represented as biochemical confirmation at 12 months.

The comparison also cannot explain why the outcome denominators differ from enrollment. Missing-data handling, analysis populations, and the statistical test are not reported in the registry record. Those limitations leave uncertainty about the analytic details in addition to the uncertainty shown by the confidence intervals.

The estimates do not establish that the program works or does not work. They describe the posted trial results and the range of group differences compatible with the reported analysis. Nor do they show that the result would be the same in settings or populations not described in the registry. The planning figures are separate illustrations and do not change the interpretation of the observed comparison.

16. Why This Trial Matters Statistically

This trial addresses a question about delivering smoking-cessation support through pharmacists in ambulatory pharmacies in Qatar. Statistically, it is useful to distinguish the intervention contrast from the outcome definition and measurement timeframe. The posted comparison concerns self-reported abstinence over the previous 7 days at 3 months, while the brief summary describes carbon-monoxide confirmation at 12 months. Those are not interchangeable descriptions, and the registry record does not explain the difference.

The example also illustrates why an estimate should be read alongside its uncertainty. The point estimate favors the intervention on the reported risk-difference scale, but its confidence interval crosses zero. The relative-measure intervals cross their no-difference value as well. A directionally favorable point estimate is not enough to establish a clear group difference when the uncertainty range includes both directions.

For clinical researchers, the record highlights the importance of complete reporting of analysis populations, missing outcomes, statistical tests, and multiplicity decisions. Those details help readers assess whether the comparison matches the intended trial question and whether the result is sensitive to analytic choices. Their absence does not prove a flaw, but it limits independent evaluation and reproducibility.

The planning illustrations further show how assumptions shape sample-size requirements. Under the stated planning approach, targeting a smaller fraction of the observed effect requires more participants per arm. These illustrations are not evidence about the trial's original design or its observed power. Keeping planning calculations separate from observed results helps prevent a design exercise from being mistaken for an outcome finding.

17. 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 limitations are specific to the registry information for this trial. The primary outcome record reports self-reported abstinence at 3 months, whereas the brief summary describes exhaled carbon monoxide confirmation at 12 months. The registry record does not explain whether the outcome definition or timeframe changed, or how these two descriptions should be reconciled.

The primary-outcome denominators are 98 for control and 101 for intervention, while enrollment is listed as 314. The adverse-event risk sets are listed as 147 and 167. The record does not explain how these counts relate to each other, report the number of missing primary outcomes, or describe participant flow. No reason for these differences can be inferred from the record.

Eligibility criteria and detailed characteristics of the enrolled participants are not reported in the registry record. The masking label is double, but the masked roles and procedures are not described. Allocation concealment and the randomization procedure are also not reported. These omissions limit evaluation of how the design was implemented and to whom the findings may apply.

The registry does not report the analysis population, missing-data method, inferential test, confidence-interval method, covariate adjustment, or multiplicity strategy. It lists 11 outcome measures, one posted secondary outcome, and zero posted analysis records. These gaps prevent a full audit of the statistical analysis and of the relation between the stated outcomes and the reported comparison. They are reporting limitations; the record alone does not establish what procedures were or were not used outside the registry.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Assessing the Effectiveness of a Pharmacist-delivered Smoking Cessation Program in the State of Qatar — NCT02123329.
• Registry record last updated 2018-01-02; status last verified 2017-06.
• Results first posted 2018-01-02.
• 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.

21. Record Summary

The registry record describes a completed, randomized, double-masked, parallel-group trial sponsored by Qatar University, with enrollment of 314. It compares a pharmacist-delivered structured smoking-cessation program with brief, unstructured pharmacist advice in ambulatory pharmacies in Qatar. The intervention description includes four face-to-face sessions, and the descriptions address nicotine replacement therapy in both arms.

The posted primary outcome is self-reported 7-day point prevalence abstinence at 3 months. The registry reports 26 of 98 in control and 31 of 101 in intervention, with a risk difference of 0.042 and an unadjusted p-value of 0.516. The confidence interval for the risk difference extends from -0.084 to 0.167.

The brief summary describes a 12-month, carbon-monoxide-confirmed outcome, but this is not reconciled with the posted primary outcome. Analysis populations, missing-data handling, and several statistical methods are not reported in the registry record.