Babies Living Safe and Smokefree: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Babies Living Safe and Smokefree (NCT02602288), a randomized na study. The primary outcome is Child Urine Cotinine.

2. Clinical Question

The study also identified maternal smoking cessation as a secondary aim. The listed secondary outcome was parent-reported, cotinine-verified 7-day point prevalence abstinence. The registry gives the outcome name but does not report its numerical results or a statistical comparison. Thus, the record describes the planned questions and interventions, but it does not provide the results needed to judge the size or precision of either outcome contrast.

3. Trial Design

Babies Living Safe and Smokefree was a randomized, double-masked, parallel-group trial. The registry lists enrollment of 396 and describes mothers screened as eligible, consented, and randomized to an experimental behavioral intervention or an attention control condition. The record does not identify which participants or study personnel were masked, or explain how masking was maintained.

The intervention operated at more than one level. WIC clinic staff used an Ask, Advise, Refer approach to ask about children's secondhand smoke exposure, advise about exposure harms, and refer mothers to smoking cessation resources. The experimental condition added telebased tobacco counseling, a smoking cessation mobile application, and nicotine replacement therapy use. The control condition added telebased nutrition counseling and a nutrition mobile application. Both conditions therefore included the clinic-level approach, while the randomized contrast concerned the additional experimental tobacco-focused program versus nutrition-focused attention control.

The study was conducted through community clinics serving families with low incomes. Recruitment was described as taking place through WIC clinics. The registry lists the status as completed, a start date of 2016-02, and primary completion on 2019-10-23. These administrative details do not establish how many participants completed each follow-up or contributed data to each endpoint; those outcome-specific numbers are not reported in the registry record.

The registry does not report a sample-size justification, the randomization procedure, allocation concealment, detailed masking procedures, or a statistical analysis plan. It also does not report interim analyses. Those omissions limit assessment of how design choices were planned and implemented. The listed design supports a randomized comparison in principle, but the available record is not enough to evaluate every operational feature or estimate the treatment effect.

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: A total of 2846 women were referred to the trial: 788 were not eligible, 647 were never reached for screening, and 709 declined to be screened. Of 702 that screened eligible, 104 refused consent and 202 could not be reached for consent or baseline. A total of 396 participants were randomized between the two arms of the study.

End of Treatment/3 Month Follow-up

Reasons for not completing this period:

12 Month Follow-up

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: At 12 month follow-up the greater number of units analyzed compared to participants analyzed in the treatment group relates to increased participant compliance with providing a urine sample. At all timepoints the fewer number of cotinines collected compared to self-report data reflects non-compliance among some participants to provide a urine sample following the telephone self-report assessments.

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 Child Urine Cotinine, measured over 3 months and 12 months.

The listed primary endpoint is child urine cotinine, expressed as log transformed ng/mL, with assessments at 3 months and 12 months. Cotinine is described in the registry as a biomarker for assessing children's secondhand smoke exposure. Unlike a report of household smoking or exposure, a biological measurement provides an objective indicator of exposure during the period reflected by the specimen, although the registry does not describe the precise collection or laboratory procedures.

The outcome description says cotinine values were log transformed to normalize their distributions. General explanation: a logarithmic transformation can make a strongly skewed continuous measure more compatible with statistical methods that work better when residuals are reasonably well behaved. It changes the scale of analysis, so a mean on the transformed scale is not directly the same as an arithmetic mean of the original cotinine concentrations. The registry identifies the endpoint unit as log transformed ng/mL and the summary parameter as a mean with standard deviation.

The investigators anticipated a greater reduction over time in the experimental group than in the control group. However, numerical endpoint values, variability estimates, and a between-group analysis are not reported in the registry record. The endpoint's purpose and measurement scale are described, but its observed results and precision cannot be assessed from the posted results.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The statistical information recorded for this trial is limited. The registry describes a randomized parallel-group comparison and a continuous primary outcome summarized as a mean with standard deviation. It does not report the actual outcome summaries or a treatment-effect analysis. The following explains the methods and concepts relevant to interpreting the recorded design, without implying that any unreported analysis was performed.

What does randomization contribute?

General explanation: randomization assigns participants to study conditions using a chance-based process. Its purpose is to make groups comparable, on average, with respect to both measured and unmeasured factors at the time of assignment. It does not guarantee identical groups, especially in any particular realized trial. The registry describes the study as randomized, but it does not report the allocation sequence, how assignments were concealed before enrollment, or the method used to generate assignments. The adequacy of those procedures therefore cannot be evaluated from the registry record.

The parallel design means the registry describes participants as assigned to one of the two conditions, rather than crossing through both conditions in sequence. The stated comparator is an attention control focused on nutrition, and both arms received the clinic-level Ask, Advise, Refer approach. Accordingly, the intended contrast is not the full program versus no contact; it is the experimental tobacco-focused additions compared with nutrition-focused additions, in the context of the shared clinic intervention. The record does not provide a formal estimand specifying how this contrast should be interpreted for participants with incomplete intervention attendance or missing outcomes.

Why use a log-transformed cotinine measure?

Child urine cotinine is continuous, and the registry specifies a mean and standard deviation as its summary. Cotinine values were log transformed to normalize distributions. General explanation: concentration measurements can have a long right tail, where a small number of relatively high values influence the mean. A logarithmic transformation compresses larger values and can reduce skewness, which may make some model assumptions more plausible. Transformation does not remove all concerns about model fit; it changes the scale on which means and differences are analyzed. The record does not specify the statistical model, how repeated measurements were incorporated, or how estimates on the transformed scale were translated for interpretation.

General explanation: a standard deviation describes the spread of individual observations around a mean on the scale being summarized. It is not the same as the uncertainty in the mean or the uncertainty in a group contrast. A confidence interval for a contrast would require an estimate and its standard error, along with the analysis details. The registry provides no numerical cotinine means, standard deviations, contrasts, or confidence intervals, so none can be interpreted.

How should repeated assessments be considered?

The endpoint timeframe lists 3 months and 12 months, and its description refers to change over time. General explanation: repeated observations from the same child are usually statistically related, so an analysis should account for that within-participant dependence rather than treating every observation as unrelated. A repeated-measures model is one possible general approach, but the registry does not identify the model used. It also does not say whether the primary test was a between-group contrast at a particular follow-up, a contrast in change over time, or an overall group-by-time comparison. Those details are not reported in the registry record.

The record's note about the number of units analyzed exceeding participants analyzed in the treatment group at 12 months suggests that the unit counted in that note may not always be a unique participant. It relates this to increased compliance with urine-sample provision. The record does not give enough detail to determine how multiple units were handled, whether repeated samples were linked within participant, or which analysis population was used.

What do the sample-size assumptions mean?

The registry describes a planning illustration based on the observed effect, with a two-sided significance level of 0.05, equal allocation between the arms, and a normal approximation. The effect to detect is expressed as a stated fraction of the observed effect. For non-time-to-event outcomes, the resulting planning quantity is participants per arm for the specified power level; time-to-event calculations would instead concern total events. No numerical sample-size results or observed-effect estimate are included in the registry record.

General explanation: such sample-size calculations ask how much information would be needed to detect a target effect under chosen assumptions. Because this illustration is based on an observed effect and scaled fractions of it, it should not be mistaken for the trial's original design justification. It is not observed power and does not show the probability that the trial detected an effect. The registry does not report the original sample-size justification, its target effect, or whether the planning assumptions used for the illustration match the trial's design.

What can be learned from the absence of analysis results?

The record lists 0 analyses. This means that the posted registry information does not contain a reported statistical analysis for the listed outcomes. It does not mean that no analyses were conducted outside the registry. Without estimates, uncertainty measures, model details, and analysis-population definitions, readers cannot verify the magnitude or precision of the treatment comparison or assess whether the prespecified objective was met.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 3 outcome measures, including child urine cotinine as the primary outcome and parent-reported, cotinine-verified 7-day point prevalence abstinence as a secondary outcome. The listed cotinine timeframe includes 3 months and 12 months. Multiple outcomes and assessment times can create multiplicity: when several comparisons are examined, the chance of at least one apparently unusual result can increase unless the analysis plan addresses that issue. General explanation: common approaches include identifying a primary comparison in advance or adjusting inference across a defined family of tests. The registry does not report a multiplicity strategy or enough analysis detail to determine which contrasts were tested.

The record lists 0 analyses and does not provide numerical results for the primary or secondary outcomes. It does not report whether the primary outcome was analyzed separately at each follow-up, as a repeated-measures contrast, or by another method. It also does not state whether any secondary outcome analyses were confirmatory or exploratory. These details are not reported in the registry record, so the risk of selective emphasis across outcomes or time points cannot be assessed.

Missing outcome information is also relevant. The registry says that fewer cotinine samples than self-report data were collected at all time points, reflecting non-compliance with providing a urine sample. It also notes that at 12 months the number of units analyzed in the treatment group exceeded the number of participants analyzed, attributing this to increased compliance with providing a urine sample. The record does not report the missing-sample counts, reasons by arm, or methods used to address missing data. It does not identify whether an analysis included all randomized participants, only those with observed measurements, or another population.

General explanation: if availability of a measurement is related to exposure, participant circumstances, or intervention participation, an analysis restricted to observed samples may not represent the randomized groups in the same way as an analysis of all randomized participants. Missing-data assumptions and sensitivity analyses help show how robust an estimate may be to such uncertainty. Those assumptions and analyses are not reported in the registry record. The absence of those details prevents assessment of the influence of incomplete specimen collection on the primary comparison.

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.

The registry lists two arms for adverse-event reporting: AAR+Behavioral Intervention (EXP) and AAR+Attention Control Intervention (CTL). For the experimental arm, 199 participants are listed at risk for serious adverse events and 199 at risk for other adverse events; the recorded counts affected are 0 in each category, with 0 deaths. For the control arm, 197 are listed at risk for serious adverse events and 197 at risk for other adverse events; the recorded counts affected are 0 in each category, with 0 deaths. No serious adverse-event terms are listed.

These are registry entries, not estimates of comparative safety. General explanation: an event count of zero means no events in that category were recorded for the listed group; it does not prove that no event occurred, that all possible harms were captured, or that the risks are identical between conditions. The record does not provide event definitions, surveillance procedures, follow-up completeness, or detail about how adverse events were attributed. It also does not report a formal statistical comparison of safety outcomes. The counts should therefore be read narrowly as the events recorded in the registry, rather than as evidence that either condition has no risk.

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

The trial record identifies a structured randomized comparison focused on reducing children's secondhand smoke exposure and promoting maternal smoking cessation. It specifies a biomarker endpoint, child urine cotinine, and describes the intervention components and attention-control condition. It also records an enrollment of 396 and safety entries for both arms. These registry entries clarify what the trial set out to evaluate and the broad form of its design.

What the posted results do not establish is whether the experimental condition led to lower cotinine, how large any difference was, or how precisely that difference was estimated. Numerical outcome summaries and statistical comparisons are not reported in the registry record. The anticipated direction of an effect is part of the endpoint description, not evidence that the effect was observed. The secondary abstinence outcome is named, but its numerical result is also not reported.

General explanation: a randomized design can support a causal interpretation when assignment, follow-up, outcome measurement, and analysis are implemented and reported appropriately. Randomization alone does not provide the missing outcome estimate, and it does not address uncertainty about missing measurements or the analysis choices. The record does not report enough detail to assess these features fully.

The registry's notes about urine-sample availability matter because cotinine is the primary endpoint. Fewer cotinine samples than self-reports were collected at all time points, and the record attributes this to non-compliance with providing urine samples. Without counts by arm, analysis methods, or sensitivity analyses, the extent to which incomplete specimen collection may affect the comparison cannot be judged.

The safety entries show zero recorded serious adverse events, other adverse events, and deaths in each arm. They are useful descriptive information, but they do not provide a complete safety evaluation or establish absence of risk. Overall, the record documents the study's question, approach, and some operational information, while leaving the central efficacy result and its uncertainty unavailable for statistical interpretation.

13. Why This Trial Matters Statistically

This trial is statistically notable for combining a clinic-level approach with additional randomized interventions delivered through counseling and mobile applications. Because both arms received Ask, Advise, Refer at the clinic level, the main randomized contrast concerns the experimental tobacco-focused program against nutrition-focused attention control, rather than intervention versus no intervention. That distinction is essential when defining what a treatment-effect estimate would represent.

The primary endpoint also illustrates a common measurement issue in exposure research: the trial considered both maternal reports and a biological measure, while identifying child urine cotinine as the primary outcome. A biomarker and a report may capture different aspects of exposure and may have different patterns of missingness. The registry notes that fewer cotinine samples than self-report data were collected at all time points. This makes completeness and handling of specimens especially relevant to interpreting any future reported comparison.

The record also shows why a stated hypothesis must be separated from an estimated effect. Investigators anticipated a greater reduction in the experimental group, but the registry does not report the numerical results needed to test that expectation. A randomized label and a completed status cannot substitute for an outcome estimate, uncertainty interval, or analysis description.

Finally, the registry's planning illustration is explicitly based on the observed effect, rather than being identified as the trial's original sample-size justification. Such illustrations can help explain the relationship between an assumed target effect and the amount of information needed, but they should not be read as observed power or evidence that an effect was established. Since the numerical illustration and outcome analyses are not reported in the registry record, the main statistical contribution available for interpretation is the design and measurement context, not a quantitative conclusion about intervention effects.

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 main limitation of the available record is that it names the primary endpoint but does not report numerical results for child urine cotinine. There are no listed group means or standard deviations, effect estimates, confidence intervals, or p-values. The secondary abstinence outcome is also named without numerical results. Consequently, the central treatment comparisons cannot be quantified or evaluated for precision.

Outcome availability may be a further concern. The registry notes that fewer cotinine samples than self-report data were collected at all time points because of non-compliance with providing a urine sample. It also reports that at 12 months more units were analyzed than participants in the treatment group, relating this to increased compliance with providing a urine sample. No counts, arm-specific missingness information, or statistical handling of these data are reported. The potential effect of missing specimens on the comparisons is therefore unclear.

Important design and analysis details are not reported in the registry record, including the randomization procedure, allocation concealment, identities of masked parties, repeated-measures model, analysis population, and multiplicity approach. The record does not report interim analyses or a sample-size justification. These omissions do not show that procedures were absent; they mean that readers cannot assess them from the registry.

The registry describes the interventions at a broad level but does not give complete details about counseling delivery, adherence, or uptake of the mobile applications and nicotine replacement therapy. It also does not provide participant characteristics or outcome-specific follow-up counts. Those gaps limit assessment of intervention implementation, population comparability, and the extent to which the analyzed data represent randomized participants.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Babies Living Safe and Smokefree — NCT02602288.
• Registry record last updated 2022-03-15; status last verified 2022-02.
• Results first posted 2022-03-15.
• 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

The registry identifies NCT02602288, titled Babies Living Safe and Smokefree, as a completed, randomized, double-masked parallel trial with enrollment of 396. It compared a multilevel tobacco-focused behavioral intervention with an attention control focused on nutrition among low-income mothers who smoke recruited through WIC clinics. Both conditions included the clinic-level Ask, Advise, Refer approach.

The primary endpoint was child urine cotinine, reported on a log transformed ng/mL scale, at 3 months and 12 months. The secondary outcome named was parent-reported, cotinine-verified 7-day point prevalence abstinence. The registry describes incomplete urine-sample collection relative to self-report data. It records zero serious adverse events, zero other adverse events, and zero deaths in each listed arm.

Numerical results for the primary and secondary outcomes, statistical comparisons, and analysis methods are not reported in the registry record. The available information therefore describes the trial design and measurement context but does not allow estimation of the intervention effect.