A Pilot Randomized Controlled Trial of Financial Incentives, Text Messaging, and Usual Care for Homeless Smokers: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Pilot Randomized Controlled Trial of Financial Incentives, Text Messaging, and Usual Care for Homeless Smokers (NCT02565381), a randomized na study. The primary outcome is Number of Participants With Biochemically-verified Smoking Abstinence, Assessed 14 Times Over 8 Weeks.

2. Clinical Question

3. Trial Design

The QUIT Smoking Study is described as a pilot randomized controlled trial with three parallel groups. Its title identifies financial incentives, text messaging, and usual care as the approaches under study. The registry lists the allocation as randomized and masking as none. The record does not describe the randomization sequence, how assignments were concealed, or any other allocation procedures; those details are not reported in the registry record.

All participants were to receive free transdermal nicotine patches and weekly in-person smoking-cessation counseling. The control group received those components alone. The financial-rewards group received the same components plus rewards contingent on biochemically verified smoking abstinence. The text-messaging group received the same components plus messages intended to support abstinence. This shared background care matters when interpreting the question: the groups differ in the added support, not in whether the listed background cessation care was offered.

The record lists overall enrollment as 83. Each of the three arm descriptions lists N=25. The registry record does not explain the relationship between the overall enrollment figure and the arm counts, so they should be reported as listed rather than reconciled by assumption. The study is marked completed. The listed start is 2015-10 and the primary completion is 2016-06.

The primary outcome was assessed repeatedly over an 8-week period. Its schedule was more frequent early in follow-up and less frequent later. This is a short-term pilot design; longer-term abstinence outcomes are not described as the primary endpoint. The record does not report a planned sample-size justification, a detailed analysis plan, or the specific procedures used to deliver or monitor each intervention.

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.

Before assignment: Some participants (N=8) enrolled in the study but did not return for randomization.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Participants with missing data at a given time point were assumed non-abstinent at that time point.

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 Biochemically-verified Smoking Abstinence, Assessed 14 Times Over 8 Weeks, measured over Point-in-time abstinence assessed in a repeated fashion 14 times over the 8-week study period.

The primary endpoint concerns participants whose smoking abstinence was verified by an exhaled carbon monoxide measurement below the stated threshold, <8ppm. The registry describes point-in-time abstinence assessed 14 times over the 8-week study period: 3 times/week for the first 2 weeks, 2 times/week for the next 2 weeks, and once every week for the last 4 weeks. The endpoint is therefore repeated across visits rather than a single assessment at the end of follow-up.

Biochemical verification gives the outcome a defined measurement criterion beyond a participant’s report of abstinence. Repeated assessment can describe whether abstinence is recorded at different points during follow-up, rather than relying only on a final visit. In general, repeated measurements also require careful interpretation: a participant can contribute observations at multiple visits, and those observations may be related to one another. They should not automatically be treated as independent pieces of evidence.

The registry specifies that missing data at a given time point were assumed to indicate non-abstinence at that time point. This is part of the endpoint’s operational definition in the record. The record does not report the number of participants meeting the criterion at each assessment, a single overall summary, or a comparison among groups. Those outcome results are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does randomization contribute?

In general, random allocation is used to make intervention groups comparable, on average, with respect to factors measured and unmeasured before assignment. That makes a between-group comparison more informative than comparing people who selected different approaches for themselves. Randomization does not guarantee identical groups in a pilot, and it does not eliminate uncertainty. The registry identifies the study as randomized, but does not report the sequence-generation or allocation-concealment methods. The record also identifies masking as none. It does not describe whether outcome assessors were masked or whether any specific steps were taken to reduce measurement or reporting bias.

What is a repeated binary endpoint?

At each assessment, the primary outcome classifies a participant as abstinent or not abstinent according to the stated exhaled carbon monoxide criterion. That is a binary outcome at a particular time point. The same participant was assessed repeatedly across the 8-week period, so the data structure includes multiple observations per participant. In general, a method that treats all those observations as independent may understate or otherwise misrepresent uncertainty when within-participant observations are associated. Statistical methods for repeated binary outcomes can account for this structure, but the registry record does not say which method, if any, was used for the primary analysis.

The endpoint title refers to the number of participants with biochemically verified abstinence, while the description specifies repeated point-in-time assessments. Those details should be read together: the record describes an abstinence count at repeated assessments, not a cumulative count of distinct people who ever abstained. It does not provide an aggregate rule for combining the repeated observations into one result.

How should missing assessments be understood?

The record states that a participant with missing data at a particular time point was assumed non-abstinent at that time point. This rule makes missingness part of the outcome classification: a missed assessment does not disappear from the endpoint definition but is treated as a non-abstinent observation for that occasion. In general, such a rule can make estimates sensitive to differences in missed visits between groups. The registry does not report the number or pattern of missing observations, nor does it describe sensitivity analyses using alternative assumptions. The stated rule should not be confused with evidence that every participant attended every assessment.

What statistical results would support interpretation?

For a between-group comparison, an effect estimate would describe the contrast being evaluated, while a confidence interval would show the range of values compatible with the data under the chosen method. In general, a confidence interval communicates precision as well as direction; a wide interval indicates greater uncertainty than a narrow one. A p-value addresses compatibility with a specified null hypothesis under assumptions of the analysis, but does not by itself describe the size or practical meaning of an effect. The registry record does not report a primary effect estimate, confidence interval, or p-value, so these interpretations cannot be applied to the trial’s primary comparison.

The registry lists 11 outcome measures, and the primary outcome itself was assessed repeatedly. In general, evaluating many outcomes or time points can increase the chance of apparently notable results arising by chance if all comparisons are treated as confirmatory. Methods may control or otherwise address this multiplicity, or investigators may distinguish primary from exploratory analyses. The registry record does not report a multiplicity strategy or enough analysis detail to determine how the repeated assessments and secondary outcomes were handled.

What can be inferred about sample size and analysis choices?

The registry record lists enrollment as 83 and gives arm descriptions with N=25 for each group, but it does not explain how those figures relate. It does not report a sample-size justification for the primary endpoint, a statistical model, covariate adjustment, an analysis population, or an interim-analysis plan. These details should not be filled in by assumption. In general, a sample-size calculation is a planning exercise based on assumptions about the outcome, effect to detect, variability, allocation, and error rates. It is not a result, and it does not establish the precision of the observed treatment contrast. A pilot study’s enrollment figure alone cannot show whether a particular effect was detectable or whether a nonsignificant result occurred.

Because the primary endpoint is repeated and binary, a single count or a simple comparison at one visit would not necessarily answer the same question as an analysis of the full series of assessments. The registry record does not identify the estimand—the precise treatment contrast intended—or specify whether the analysis focused on each time point, an average pattern, or another summary. Without reported results and methods, readers can describe the measurement design but cannot reconstruct the inferential analysis.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 11 outcome measures. The primary abstinence outcome was assessed at 14 time points, and the record also lists secondary outcomes addressing abstinence at the end of the study, cigarette consumption, behavioral health, study and counseling attendance, and nicotine patch use. Examining multiple outcomes or time points raises a general multiplicity issue: the more comparisons considered, the more important it becomes to distinguish confirmatory questions from exploratory ones and to describe any adjustment strategy. The registry record does not report a multiplicity plan or explain how repeated assessments were combined or compared.

The registry record does not report statistical analyses or results for the primary endpoint. It also does not report an analysis population, such as whether analyses were based on all randomized participants or on a subset with available data. That population definition is important because it tells readers who contributes to an estimate and how participants with incomplete follow-up are handled.

One missing-data rule is reported: missing data at a given time point were assumed non-abstinent at that time point. This is a specific classification rule, not a complete description of the missing-data pattern. The number of missing assessments, reasons for missingness, and sensitivity analyses are not reported in the registry record. In general, conclusions can depend on how missing outcomes are treated, especially if missingness differs across groups or relates to abstinence. No further assumptions should be attributed to the study from the posted record.

The protocol’s sample-size justification, any interim analyses, and the detailed statistical plan are not reported in the registry record. Consequently, the available information does not establish how the investigators intended to handle the multiple outcomes, time points, missing observations, or analysis populations.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent non-serious adverse event terms

The posted adverse-event figures list 25 participants at risk in each of the three groups. Serious adverse events affected 0 participants in the control group, 0 in the financial-rewards group, and 0 in this discussion-messaging group. Deaths are listed as 0 in all three groups. For other adverse events, the record lists 1 affected participant in the control group, 0 in the financial-rewards group, and 5 in this discussion-messaging group.

These are participant counts, not event rates, and the record does not provide event descriptions for the other adverse events. The serious-adverse-event section lists no serious-event terms. The figures therefore describe what was recorded in these summaries, but do not identify the nature, timing, severity beyond the category, or relatedness of the other events. Those details are not reported in the registry record.

In general, zero observed serious events in a trial does not establish that an event is impossible or that the underlying risk is zero. Safety counts are interpreted in light of the number of participants observed and the duration and completeness of follow-up. The registry describes an 8-week study period for the primary endpoint, but does not provide a detailed adverse-event collection schedule or further safety-analysis methods. These counts should be read as descriptive summaries, not as a definitive comparison of safety between groups.

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

The registry record describes a pilot comparison of two added support strategies against a control condition in which participants received nicotine patches and in-person counseling. It gives a clear operational definition for the primary outcome: point-in-time smoking abstinence assessed with an exhaled carbon monoxide threshold of <8ppm, repeatedly over the 8-week study period. It also states how missing data at an assessment were classified.

That design information is not a report of comparative efficacy. The primary abstinence counts by group, the between-group estimates, and their uncertainty are not reported in the registry record. Without those results, the direction and size of any observed difference cannot be described. The record therefore cannot support a claim that either added approach increased or decreased abstinence relative to the control condition.

Nor does the absence of a reported analysis mean that the groups were identical or that there was no effect. In general, a finding of no statistically detectable difference, if reported, would not itself prove equivalence; interpretation would depend on the estimate, its precision, and the prespecified question. None of those primary-comparison statistics appears in the registry record.

The study is explicitly identified as a pilot. Its arm descriptions list N=25 per group, while the record lists enrollment as 83 and does not reconcile the figures. The available record also does not provide a sample-size justification, analysis population, or detailed statistical plan. These limits constrain how much can be concluded from the design description and adverse-event summaries. The posted data support a description of the intended comparison and measurement approach, but not an estimate of comparative abstinence outcomes.

13. Why This Trial Matters Statistically

This trial is statistically notable because it evaluates added cessation-support approaches against a shared background of nicotine patches and weekly in-person counseling. That design frames the comparisons around the added financial rewards or text messages, rather than the effect of receiving cessation support versus receiving none. The distinction is important when stating what the trial was designed to compare.

The primary outcome was measured repeatedly, with a schedule that changed over the course of the 8-week study period. Repeated data can provide information about patterns over time, but they also create analytic choices: the relationship between measurements from the same participant, the handling of missed visits, and the summary used for the group comparison all matter. The registry documents the abstinence definition and a missing-data rule, but does not report the statistical method or primary results.

The record also illustrates why a trial’s design description and its outcome evidence must be kept separate. Randomization and a specified biochemical measure describe how the comparison was structured. They do not, without reported group results and uncertainty, establish the direction or precision of an intervention effect. Similarly, adverse-event counts are useful descriptive information but do not substitute for the missing primary outcome analysis.

As a pilot, the study can be understood as an investigation of three approaches in a particular population and setting. The registry record does not report a sample-size rationale or analysis results that would permit a quantitative assessment of the primary comparison. Its statistical contribution in the posted record is therefore principally the documented design, outcome definition, assessment schedule, and missing-data rule.

14. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The registry record’s most consequential limitation for statistical interpretation is that it does not report primary outcome counts, estimates, confidence intervals, or p-values. The repeated endpoint is defined, but the group-specific abstinence findings are absent. The record also does not report results for the listed secondary outcomes, so those outcomes cannot be used to supplement the primary comparison.

The study is a pilot, and the arm descriptions list N=25 in each group. Overall enrollment is listed as 83, but the registry does not explain how that figure relates to the arm counts. The number of participants contributing observations at each assessment is not reported. Accordingly, neither the exact analyzed sample nor the completeness of repeated follow-up can be established from the record.

Masking is listed as none. The registry does not describe whether biochemical outcome assessors were masked, and it does not provide other procedures for limiting bias. It also does not report the randomization method, allocation concealment, analysis population, statistical model, multiplicity approach, or sample-size justification. These omissions prevent assessment of important design and analysis decisions; they do not show what procedures may have been used outside the registry record.

The primary follow-up period is 8 weeks, and the record does not describe longer-term abstinence assessment. The missing-data rule treats a missed time point as non-abstinent, but the missingness pattern and any sensitivity analyses are not reported. The safety summaries provide participant counts but no event descriptions for other adverse events. Together, these limits restrict interpretation to the design and reporting details that the registry documents.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: A Pilot Randomized Controlled Trial of Financial Incentives, Text Messaging, and Usual Care for Homeless Smokers — NCT02565381.
• Registry record last updated 2017-07-14; status last verified 2017-06.
• Results first posted 2017-07-14.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

18. Record Summary

NCT02565381 is the completed QUIT Smoking Study, a pilot randomized controlled trial with three parallel groups and no masking listed. It studied homeless cigarette smokers and compared usual care consisting of transdermal nicotine patches and in-person counseling with the same care plus contingent financial rewards or text messages. The primary endpoint was biochemically verified point-in-time smoking abstinence assessed 14 times over the 8-week study period, using an exhaled carbon monoxide threshold of <8ppm. Missing data at a time point were assumed non-abstinent.

The registry lists enrollment as 83 and gives N=25 for each arm; it does not explain the relationship between those figures. Serious adverse events and deaths are listed as 0 in all groups. The primary abstinence results, statistical analyses, and detailed analysis plan are not reported in the registry record, so comparative outcome estimates and their precision cannot be assessed from the posted information.