Vaping THC From Electronic Cigarettes: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Vaping THC From Electronic Cigarettes (NCT02955329), a randomized phase 3 study. The primary outcome is Mean Delivered and Retained Doses.

2. Clinical Question

3. Trial Design

This is a randomized, single-blind, phase 3 crossover study listed as completed. The registry describes three vaping conditions: cannabis leaf, tobacco containing nicotine, and cannabis leaf with tobacco containing nicotine. Participants were intended to receive all three conditions, with the order counterbalanced between subjects. The brief summary describes three outpatient visits separated by at least 48 hours. Participants were to be blinded to vaporizer contents on the study day, although the summary says they would be told during screening that they would vape cannabis alone, tobacco alone, and cannabis plus tobacco with nicotine.

The record names nicotine and cannabis as drug interventions and the PAX loose-leaf vaporizer as a device. The arm descriptions characterize the tobacco condition as vaping tobacco leaves with nicotine, the cannabis condition as vaping marijuana leaves with THC, and the combined condition as vaping flavorless 6% nicotine e-liquid followed by THC. These descriptions are the registry’s account of the conditions; the record does not give more detailed dosing or administration procedures.

The enrollment field reports 8 participants, and each of the three posted outcome arms has a sample size of 8. In contrast, the brief summary describes 14 smokers of tobacco cigarettes and cannabis. The record does not explain this difference, so the enrollment field and outcome sample sizes should not be treated as evidence that the planned and analyzed populations were identical. The study dates are listed as starting 2019-03-20, with primary completion on 2019-11-30. The registry does not report the number of participants who completed all visits or the analysis population used for the endpoint.

A crossover design allows each participant to contribute observations under multiple conditions. That feature can support within-person comparisons, but interpretation depends on how the repeated observations are analyzed and on whether order or carryover effects are addressed. Those analysis details are not reported in the registry record. The posted results give arm-level means and standard deviations, rather than paired treatment contrasts.

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 8 total participants received all 3 interventions over the course of 3 days, with the sequence of the interventions varied for each participant. The order of treatment (cannabis leaf, tobacco with nicotine, cannabis leaf \& tobacco with nicotine) will be counterbalanced between subjects

Tobacco Arm

Cannabis Arm

Combined Cannabis and Tobacco Arm

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 Mean Delivered and Retained Doses, measured over Study Day 1-3.

The primary endpoint is titled Mean Delivered and Retained Doses, uses grams (g), and is summarized as a mean with a standard deviation. Its timeframe is Study Day 1-3. The registry describes delivered THC and nicotine doses as estimates based on the change in e-cigarette weight multiplied by the THC or nicotine concentration in e-liquid. It describes systemically retained amount as delivered dose minus the amount in gas traps.

These measures are intended to characterize how much of the relevant substance is delivered during vaping and how much is estimated to remain systemically after accounting for material captured in the traps. In pharmacokinetic research, such exposure measures can help describe intake and potential variation in delivery across conditions. That is a general explanation of the role of dose measures, not evidence of a clinical effect.

The posted summaries report a mean of 0.016 g with standard deviation 0.003 for the Tobacco Arm, 0.018 g with standard deviation 0.008 for the Cannabis Arm, and 0.026 g with standard deviation 0.008 for the Combined Cannabis and Tobacco Arm. The registry record does not clarify whether each reported arm value is delivered dose, retained dose, or a particular THC or nicotine measure. It also does not report separate endpoint results for delivered and retained dose by analyte. That limits the extent to which the figures can be assigned a specific biological interpretation.

Although the endpoint description refers to both delivery and retention, the posted summary statistics alone do not show individual participant trajectories or paired differences across conditions. The registry record does not report confidence intervals or hypothesis tests for these summaries.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a mean and standard deviation describe?

The mean is a measure of the average value in a group. For this endpoint, the registry reports means in grams. The standard deviation describes how spread out observations are around that group mean. A smaller standard deviation indicates observations more tightly clustered around the mean, while a larger one indicates more variation. These summaries do not show the full distribution, and they do not indicate how precisely a mean is estimated. Precision of a mean is often conveyed with a confidence interval, but confidence intervals are not reported in the registry record.

For the posted arms, the mean and standard deviation are 0.016 g and 0.003 for tobacco, 0.018 g and 0.008 for cannabis, and 0.026 g and 0.008 for the combined condition. Those are descriptive summaries. A standard deviation is not a confidence interval, and it should not be read as a margin of error around the mean. Without participant-level observations or additional inferential statistics, the summaries cannot establish how precisely the conditions differ.

Why is the crossover structure important?

In a crossover trial, participants receive more than one study condition. Each participant can therefore act as their own comparison, which may reduce the influence of stable differences between people. A suitable analysis commonly uses paired observations, because measurements from the same person are related. The uncertainty of a paired contrast depends on the pattern of within-person differences, not just on the separate arm means and standard deviations.

The record identifies a randomized crossover model and says that the order of treatment was to be counterbalanced. It does not report the statistical method used to analyze repeated measurements, whether period or sequence effects were assessed, or how carryover was considered. The posted arm summaries do not show the within-person differences needed to reconstruct a paired contrast. As a result, they are not enough to evaluate the crossover comparison statistically.

What would a confidence interval add?

General: A confidence interval describes a range of values compatible with the data and a specified statistical procedure. For a treatment contrast, it communicates both the estimated direction and the precision of that contrast. A narrow interval indicates greater precision than a wide interval, while an interval spanning values on different sides of a null contrast can reflect substantial uncertainty. No confidence interval for an arm contrast is reported in the registry record, so the precision of differences among these conditions cannot be assessed from the posted summaries.

What does a hypothesis test add?

General: A hypothesis test evaluates how compatible the data are with a specified null hypothesis under chosen model assumptions. A p-value is not the probability that the null hypothesis is true, nor does it measure the size or importance of an effect. The registry record lists no analyses and provides no p-values for the primary endpoint. There is therefore no posted hypothesis-test result to interpret, and the descriptive differences among arm means should not be called statistically significant or nonsignificant.

How should the planning illustrations be read?

General: Sample-size planning asks how many participants would be needed under specified assumptions to detect a chosen effect with a chosen power and significance level. The registry record’s stated planning approach uses a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the target effect set as a stated fraction of an observed effect. These are planning illustrations based on the observed effect, not the trial’s own design rationale and not observed power. The registry record does not report the trial’s sample-size justification. No planning sample-size values are described in the registry results, so none should be interpreted as actual enrollment or evidence about the trial’s ability to detect an effect.

General: Over-dispersion means that observed variation is greater than a statistical model expects. When present, it can make conventional standard errors too small and confidence intervals too narrow if the model does not account for it. The registry record does not provide a model, distributional checks, or enough detailed outcome data to assess over-dispersion for this endpoint. The arm-level standard deviations alone do not establish whether over-dispersion occurred.

Why do the endpoint details matter?

The endpoint description combines delivered and retained dose and refers to both THC and nicotine. The posted arm summaries give a single mean and standard deviation for each condition, but do not identify the analyte or distinguish delivered from retained dose in those values. A model or contrast can only be interpreted clearly when the analyzed outcome is defined. Since the registry does not specify which endpoint component corresponds to each reported number, assigning the values to a particular chemical or dose stage would go beyond the record.

For a crossover analysis, period and sequence can also matter because order is part of the treatment experience. Counterbalancing is described in the brief summary, but the record does not report whether the realized treatment orders were balanced, whether period effects were modeled, or whether the interval between visits was incorporated into analysis. These are not assumptions that can be settled from the means and standard deviations.

Finally, a statistical analysis plan, missing-data approach, and analysis population are not reported in the registry record. Those details affect how the analysis should be understood, especially when a crossover design requires measurements under multiple conditions for the same participant. The available summaries allow a descriptive account of the recorded arm values, but do not support reconstruction of the intended or executed inferential analysis.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Tobacco Arm", "Cannabis Arm", "Combined Cannabis and Tobacco Arm")
n   <- c(8, 8, 8)
m   <- c(0.016, 0.018, 0.026)
sp  <- c(0.003, 0.008, 0.008)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Tobacco Arm  8  0.016  0.003  0.013  0.019
CARM  Cannabis Arm  8  0.018  0.008  0.011  0.025
CARM  Combined Cannabis and Tobacco Arm  8  0.026  0.008  0.019  0.033

11. Multiplicity, Missing Data and Analysis Populations

The study has three vaping conditions and a primary endpoint description encompassing delivered and retained doses of THC and nicotine. The registry record does not report how many primary comparisons were planned, whether dose components were treated as separate outcomes, or how multiplicity was addressed. Multiplicity arises when several hypotheses are tested: the chance of at least one false-positive finding can increase as the number of tests grows. General methods can control this risk, but the registry record does not identify a procedure or provide tests to which one could apply it.

The record lists 11 outcome measures and no posted secondary outcome results. It lists no analyses. It does not state whether unreported outcomes were not collected, not analyzed, or not posted. The statistical analysis plan and any prespecified hierarchy of outcomes are not reported in the registry record, so the distinction between planned and exploratory analyses cannot be assessed.

Missing-data handling is also not reported in the registry record. For a crossover study, it matters whether participants have usable measurements under all conditions and how incomplete visit sequences are handled. The outcome summaries list 8 participants per arm, but do not establish whether the same 8 people contributed to every condition, whether any measurements were missing, or whether an analysis used a complete-case subset. The record does not report imputation, sensitivity analyses, or reasons for missing observations.

The analysis population is not reported in the registry record. It is therefore unclear whether the summaries include all enrolled participants, all who completed treatment conditions, or only those with endpoint measurements. The brief summary’s figure of 14 participants differs from the enrollment field’s 8, and the record does not explain that discrepancy. These omissions limit assessment of selection and missing-data bias.

12. Safety Results

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

Deaths

Other (non-serious) adverse events

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

The adverse-event data list 8 participants at risk in each of the Tobacco, Cannabis, and Combined Cannabis and Tobacco arms. Serious adverse events are recorded as 0 in each arm, and deaths are also recorded as 0 in each arm. Other adverse events are recorded as 0 in each arm. No serious adverse event terms are listed.

These counts describe what is posted in the registry record for the reported groups. A zero count means no event was recorded in that category in the posted data; it does not prove that the risk is absent. With 8 participants listed per arm, the data provide limited information about uncommon events. The record does not report event definitions, severity grading beyond the serious-event category, exposure-adjusted rates, or confidence intervals around event frequencies.

The record does not explain whether the same participants contributed safety data under all conditions, or how adverse events were assigned in this crossover design. It also does not provide a detailed list of non-serious event terms. The zero counts should therefore be interpreted as a description of the posted safety results, not as a complete characterization of safety or a comparison of risks between conditions.

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

The posted results support a descriptive statement about the recorded mean dose summaries: the Tobacco Arm is reported at 0.016 g, the Cannabis Arm at 0.018 g, and the Combined Cannabis and Tobacco Arm at 0.026 g. The corresponding standard deviations are 0.003, 0.008, and 0.008. Each arm lists 8 participants. The registry record does not provide inferential comparisons, so these numbers do not establish that one condition differs statistically from another.

The results also do not establish the size or precision of a within-person effect. This is a crossover trial, but no paired contrasts or participant-level data are posted. Separate arm means cannot substitute for paired estimates because the relationship between each participant’s measurements across conditions is not visible. Confidence intervals and p-values for contrasts are not reported in the registry record.

The endpoint’s interpretation is constrained by the way it is described and summarized. The title and endpoint description refer to delivered and retained THC and nicotine doses, but the arm summaries do not identify which analyte or dose component each number represents. Consequently, the values should not be presented as a definitive measure of a particular chemical’s delivered or retained amount without further specification in the registry record.

The trial record also does not provide a basis for conclusions about clinical benefit or harm. It describes dose estimation and safety monitoring, not a clinical outcome comparison. The adverse-event counts are zero in the posted categories for each arm, but that is not evidence that no risk exists. The sample sizes and absence of inferential safety estimates limit what can be learned about event frequency.

In short, the registry results describe arm-level dose summaries and recorded adverse-event counts. They do not show whether the conditions differ after accounting for the crossover design, how precise any contrast would be, or what the results mean for clinical outcomes. The enrollment discrepancy and unreported analysis details add uncertainty about the population and statistical interpretation.

14. Why This Trial Matters Statistically

This trial raises statistical issues that are common in small pharmacology studies. A crossover design can be informative because each participant experiences multiple conditions, making within-person contrasts central to the analysis. The posted registry results, however, provide arm-level means and standard deviations rather than paired contrasts. This illustrates why the design label alone is not enough to determine how evidence for a treatment comparison should be interpreted.

The endpoint also shows the importance of precise outcome definition. Delivered dose and retained dose are related but distinct quantities, and THC and nicotine are distinct analytes. The registry description mentions both, while the posted summaries do not specify which quantity each value represents. Clear endpoint mapping is necessary for readers to understand what a numerical result measures and for analysts to know which model is appropriate.

Small group summaries can describe observed values, but they do not automatically provide reliable evidence about between-condition differences. The absence of confidence intervals and tests means that the uncertainty around contrasts is not available in the registry results. It also highlights the distinction between a sample-size planning illustration and evidence from an actual analysis. Planning values based on an observed effect are not a measure of observed power.

Finally, the record contains an unresolved enrollment difference: the enrollment field and arm summaries report 8, while the brief summary describes 14 participants. The registry does not explain the relationship between those figures. Transparent reporting of participant flow, analysis populations, missing data, endpoint definitions, and paired estimates would make the statistical evidence easier to evaluate. These details matter not as formalities, but because they determine which observations support each conclusion.

15. Limitations

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

The registry record does not explain why the enrollment field reports 8 participants while the brief summary describes 14 tobacco-cigarette and cannabis smokers. The arm-level outcome summaries list 8 participants in each condition, but the record does not say whether those are the same participants across all three arms or whether they represent a subset of the people described in the summary.

The outcome description and posted summaries are not fully aligned in specificity. The primary endpoint title refers to delivered and retained doses, and the definition refers to both THC and nicotine. Yet the arm summaries provide only one mean and standard deviation for each condition and do not identify the analyte or dose component represented. Separate results for delivered versus retained amount are not reported in the registry record.

Although the study is described as randomized and crossover, the statistical analysis of repeated measurements is not reported in the registry record. Paired contrasts, treatment-order results, period effects, carryover assessment, confidence intervals, and p-values are not posted. The summaries therefore do not permit a direct evaluation of the within-participant treatment comparisons that are central to this design.

The record does not report the analysis population, participant flow, missing-data methods, or whether all participants completed each condition. It also does not provide the statistical analysis plan or sample-size justification. The stated planning approach is an illustration based on an observed effect, not the trial’s own design basis; no planning values are included in the registry entries analyzed.

For safety, the posted counts are zero for serious events, other events, and deaths in each arm, but event definitions, detailed non-serious event terms, and uncertainty estimates are not reported. Taken together, these limitations mean that the registry offers a basic descriptive account but not a complete statistical assessment of efficacy, exposure contrasts, or safety.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Vaping THC From Electronic Cigarettes — NCT02955329.
• Registry record last updated 2023-06-29; status last verified 2023-06.
• Results first posted 2021-04-30.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

19. Record Summary

NCT02955329, titled Vaping THC From Electronic Cigarettes, is listed as a completed, randomized, single-blind, phase 3 crossover study sponsored by the University of California, San Francisco. The registry dates are 2019-03-20 for study start and 2019-11-30 for primary completion. The brief summary describes three vaping conditions and a counterbalanced treatment order across outpatient visits.

The primary endpoint is titled Mean Delivered and Retained Doses, is measured in grams, and is summarized by mean and standard deviation over Study Day 1-3. Posted arm summaries list 8 participants per condition and means of 0.016 g for tobacco, 0.018 g for cannabis, and 0.026 g for the combined condition. The endpoint component represented by each arm value is not specified. No analyses are listed, and the record does not report inferential comparisons. Serious adverse events, other adverse events, and deaths are recorded as 0 in each arm. The enrollment field reports 8, while the brief summary describes 14; the registry does not explain this difference.