Human Perception of Odors and Odor Blockers: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Human Perception of Odors and Odor Blockers (NCT06191419), a na na study. The primary outcome is Cigarette Purchase Task.

2. Clinical Question

The registry frames the broader aim as determining whether blockers of cigarette-smoke odor perception have utility in smoking cessation. Participants were to smell up to 20 odor samples per session and report odor pleasantness and desire to smoke. These tasks examine responses to odor conditions; they do not, by themselves, establish whether a blocker changes smoking behavior over time or supports cessation.

The distinction between the stated research question and the registered primary measure matters. The question focuses on perceived odor intensity and urge to smoke, while the primary endpoint is a purchase-task measure. Odor pleasantness is listed as a secondary outcome. Numerical results for these measures are not reported in the registry record, so the record does not show the observed pattern of responses or quantify how closely the primary endpoint addresses the stated question.

3. Trial Design

The registry record identifies this as a completed, single-group study with an enrollment of 27. Allocation is listed as NA and masking as NONE. The study is therefore not a randomized, masked, between-arm comparison. Its design description concerns participants who smoke smelling odor samples and reporting their responses.

The described samples include clean air, an irrelevant odor, blocking odors, cigarette smoke, and cigarette smoke combined with blocking odors or irrelevant odors. These sample types provide different odor experiences within the study task. The record does not describe a separate randomized control arm, and the listed sample conditions should not be interpreted as independently assigned trial groups.

The registered intervention is Odorants, classified as OTHER. Participants were asked to smell up to 20 samples per session. The registry does not report the number of sessions each participant completed, the order in which samples were presented, or whether presentation order was randomized. It also does not report details about participant instructions beyond smelling samples and reporting on pleasantness and desire to smoke.

The study is marked COMPLETED, with a primary completion date of 2025-05-15 and a start date of 2024-04-05. Those status and date fields describe the registry record; they do not establish how many participants completed every task or contributed data to each outcome. The registered enrollment is 27, but the number analyzed for each measure is not reported in the registry record.

Because there is no randomized comparison, any observed response differences among odor samples would need to be interpreted as within-study contrasts rather than evidence from a like-for-like comparison of treatment arms. The registry record does not report outcome estimates or analyses that would show the size or precision of any such contrasts. It also does not report a protocol-level account of the statistical analysis plan or sample-size justification.

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: All participants assessed for eligibility were enrolled and started the study procedures.

Overall Study

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Cigarette Purchase Task, measured over 3 hours (total for all outcome measures).

The primary endpoint is the Cigarette Purchase Task, measured as a mean on a log (US Dollars) scale, with standard deviation as the registered measure of dispersion. In the task, a smoker selects how much they are willing to spend for a single cigarette of their preferred brand from 19 listed amounts ranging from $0.00 (free) to $1,120. The measure is the breakpoint at which the participant is no longer willing to purchase.

A purchase task is used to characterize stated demand for a cigarette under the task’s hypothetical price choices. A breakpoint condenses a sequence of choices into a point where willingness to purchase stops. It is a behavioral measure within the task, not a direct count of cigarettes smoked, a record of actual purchases, or a measure of cessation.

The registry describes the task data as skewed and says they are log transformed after adding 0.01 for statistical analysis. A log transformation can make a strongly right-skewed distribution more suitable for some statistical summaries and models. The registered endpoint is therefore on a transformed scale; its mean is not directly a mean amount of money spent in ordinary US dollars.

The timeframe is 3 hours (total for all outcome measures). The registry does not report numerical endpoint results, a confidence interval, or an analysis estimate. Thus, the endpoint’s definition and scale are available, but the observed mean and its precision are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies a continuous primary measure summarized as a mean, with standard deviation as its dispersion measure. It also describes the measure as log (US Dollars). These fields specify the intended scale and summary, but they do not provide a numerical estimate or a full account of the statistical methods used. No analyses are listed in the registry record.

What does a mean summarize?

For a continuous outcome, the mean is an average of the measured values on the scale being analyzed. It provides a measure of location, while the standard deviation describes how spread out values are around that mean. These summaries are most directly interpretable when the distribution is reasonably represented by its center and spread. If observations are strongly skewed, a small number of large values can influence the mean and standard deviation, and those summaries may not describe a typical participant’s response particularly well.

The registry specifically says Cigarette Purchase Task data are skewed. It also says the values are log transformed after adding 0.01 for statistical analysis. Log transformation changes the scale: equal differences on a log scale do not correspond to equal differences in dollars. A mean calculated after transformation is an average of transformed values, not the arithmetic average of the original spending amounts. The registry does not identify the logarithm base, so that detail is not reported in the registry record.

Why add a constant before transformation?

As a general statistical point, the logarithm of zero is undefined. A task that permits a free option can therefore create a zero amount, and adding a constant before taking a logarithm is one approach to making zero-valued observations transformable. The record specifies that 0.01 is added, but it does not provide a fuller justification for that choice. The constant affects the transformed values, especially values near zero, so the result should be interpreted on the stated transformed scale rather than casually translated into ordinary dollar amounts.

What does the standard deviation tell the reader?

The standard deviation is a measure of dispersion, not an estimate of uncertainty in the mean. It describes variation among observations on the scale used for analysis. A confidence interval for a mean, by contrast, would quantify uncertainty around the estimated mean under the analysis assumptions. The registry gives the dispersion measure planned for the endpoint, but it reports neither a numerical standard deviation nor a confidence interval. The amount of variability and the precision of the primary estimate therefore cannot be evaluated from the record.

What would a comparison mean in a single-group study?

The study is listed as SINGLE GROUP, with allocation NA and masking NONE. Its odor samples include controls and odor combinations, but these are not registered as separate randomized arms. In general, a comparison of repeated responses to different samples can describe how responses vary across those conditions. It does not automatically support the same interpretation as a randomized treatment-control contrast. The registry does not report how samples were ordered or assigned, or the methods used to account for repeated observations from the same participant.

Repeated observations from a participant tend to be related rather than independent. General statistical methods for repeated measurements account for this dependence when estimating uncertainty. Treating each response as unrelated could understate or otherwise misstate uncertainty. The registry record does not describe the unit of analysis, a repeated-measures model, or another method for handling within-participant dependence. These details are not reported in the registry record.

Why does over-dispersion matter?

In general, over-dispersion means that observed variability is greater than a statistical model assumes. When the model understates variability, standard errors and confidence intervals may be too narrow, and significance tests may be poorly calibrated. The registry does not state that an over-dispersion adjustment was used, and the primary endpoint is described as a transformed continuous outcome rather than a count outcome. The broader point is that uncertainty calculations depend on whether the model represents the observed spread and dependence adequately.

The registry describes a planning illustration based on an observed effect fraction, a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. This is a planning convention, not a description of the registered single-group design. Planning sample sizes are hypothetical estimates of the participants needed under stated assumptions; they are not observed results, and they are not observed power. The registry’s effect estimate and numerical planning outputs are not reported in the registry record, so the illustration cannot be checked or interpreted as a design justification.

In short, the endpoint definition identifies a transformed continuous measure and its intended descriptive summaries. The record does not provide the observed values, a model specification, an uncertainty estimate, or sufficient analysis detail to assess assumptions. Those omissions limit statistical interpretation even though the outcome’s task and scale are described.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 3 outcome measures and 0 analyses. It names the Cigarette Purchase Task as the primary outcome and Odor Pleasantness Score as a secondary outcome. Numerical results and analysis details are not reported in the registry record. The record does not describe a multiplicity adjustment, a hierarchy among outcome tests, or which outcomes were included in any statistical testing. Therefore, the potential effect of examining multiple outcomes cannot be assessed.

Multiplicity is a general concern when several outcomes or comparisons are examined: the more opportunities to identify a nominally notable result, the greater the chance that some apparent finding arises by chance. Methods such as prespecifying a primary endpoint or adjusting inference can address particular multiplicity concerns, but the registry record does not establish whether such methods were planned or applied. The listed primary and secondary outcomes alone do not establish the full analysis plan.

The record also does not report how missing observations were handled, how many participants contributed data to each outcome, or whether any participants were excluded from an analysis. Enrollment is 27, but enrollment is not the same as the analysis population. There is no information about incomplete sessions, missing task responses, or reasons for missing data. It would be inappropriate to assume that all enrolled participants completed every measure or that missingness had no effect.

Analysis populations are not described. The record does not report whether analyses included all enrolled participants, only participants with usable measurements, or another defined group. It also does not provide participant flow or outcome-specific denominators. These omissions prevent readers from checking how the analyzed participants relate to the registered enrollment and from assessing whether results may be sensitive to missing-data decisions.

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 safety fields report that 27 participants were at risk for serious adverse events and 0 were affected. For other adverse events, 27 were at risk and 0 were affected. Deaths are reported as 0. No top serious adverse-event terms are listed.

These figures describe the adverse-event counts recorded in the registry for the listed group, Participants That Smoke. They do not show that every possible adverse event was measured, nor do they establish the completeness of event reporting. The registry record does not describe event definitions, monitoring procedures, the observation period for safety, or whether events were judged related to the odor samples.

A count of zero means that no events in that category are reported in this record; it does not prove that the risk is absent. The number at risk is the reported safety denominator, not necessarily the number with complete data for every outcome. The safety counts should be read as registry-recorded events for this study, rather than as a comparison of safety between randomized groups, because the design is single-group.

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

The registry record establishes that a completed, single-group study of odor perception and cigarette-related measures was registered, with an enrollment of 27. It describes odor samples, participant reports about pleasantness and desire to smoke, and a primary Cigarette Purchase Task endpoint. It also gives the endpoint’s transformed scale and the intended mean and standard deviation summaries.

Those details do not reveal whether odor blockers changed perceived intensity, desire to smoke, or purchase-task responses. Numerical outcome results are not reported in the registry record, so the direction and magnitude of any observed response are unknown from this record. No confidence interval, p-value, or analysis estimate is available to describe precision or statistical compatibility.

The study’s stated interest in possible relevance to smoking cessation should not be confused with a direct test of cessation. The described tasks capture responses to odor samples and willingness to spend for a cigarette in a purchase task. The registry does not report a cessation outcome, changes in smoking over time, or actual cigarette purchasing behavior. The task measure is not itself evidence about whether participants stopped smoking.

The design also limits the kind of comparison represented. This is not a randomized comparison between treatment arms, and the sample conditions are described within a single-group study. Any response contrasts would need interpretation in light of that design and the unreported details about sample ordering and analysis. The completion status indicates the study is marked completed, but it does not supply the missing results.

The appropriate conclusion is therefore narrow: the registry documents the research question, study structure, endpoint definition, and safety counts, but does not report findings that answer the primary question. Neither benefit nor lack of benefit can be inferred from the absence of numerical outcome results.

13. Why This Trial Matters Statistically

This study is statistically interesting because its scientific question concerns responses to odor conditions, while its primary endpoint is a purchase-task breakpoint. That makes it important to distinguish what the study measures directly from the broader behavioral question it seeks to inform. Odor pleasantness is listed as a secondary outcome, and the description also mentions reports of desire to smoke, but numerical results are not reported in the registry record.

The endpoint’s transformation is another important interpretive feature. The registry notes skewed task data and specifies a log transformation after adding 0.01. Analysis on a transformed scale may be suitable for data with a skewed distribution, but a mean on that scale is not the same as a mean dollar amount. Clear reporting of the scale, effect estimate, and uncertainty would be needed for readers to understand the result.

The single-group structure also calls for care. Odor controls and mixtures can be part of a structured task without constituting randomized treatment arms. Statistical interpretation depends on how conditions were presented and how repeated responses from a participant were handled. Those details are not reported in the registry record.

Finally, the record illustrates the difference between registration and results reporting. It identifies a completed study, the registered enrollment, and a primary outcome, but it lists no analyses and provides no numerical outcome estimates. Without those results and analysis details, readers cannot judge effect size, precision, or the relationship between the primary measure and the stated question. The study’s statistical relevance lies partly in making these distinctions explicit.

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 for interpreting this trial from the registry record is the absence of numerical outcome results. Although the study is marked completed and the primary endpoint is defined, the record does not report an endpoint estimate, dispersion value, confidence interval, or p-value. It is therefore not possible to characterize the observed responses or their precision.

The single-group design is another limitation for causal interpretation. The registry lists no randomized allocation and describes multiple odor sample types within the study, not separate randomized arms. The record does not explain sample ordering, assignment, or control of possible order effects. The odor conditions therefore cannot be treated as randomized trial groups on the basis of the registry description.

Some essential analysis details are also absent. The record does not report the statistical model, how repeated responses were handled, the logarithm base, or whether assumptions were assessed. It does not report participant flow, outcome-specific analysis counts, missing-data methods, or the analysis populations. These gaps make it difficult to assess the robustness or reproducibility of any outcome analysis.

The primary measure is a log-transformed purchase-task breakpoint, not a direct measure of actual purchasing or cessation. Although the study’s stated motivation concerns smoking cessation, the registry does not report a cessation outcome or a follow-up measure of smoking behavior. The extent to which the primary endpoint captures the broader research question cannot be established from the record alone.

Finally, the record does not provide a protocol-level sample-size justification or a detailed statistical plan. A planning illustration is described, but the observed effect and numerical planning outputs are not reported in the registry record. The illustration therefore cannot be used to evaluate whether enrollment was adequate for the study’s intended comparisons.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Human Perception of Odors and Odor Blockers — NCT06191419.
• Registry record last updated 2026-07-23; status last verified 2026-06.
• Results first posted 2026-07-08.
• 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 record identifies NCT06191419 as a completed, single-group study titled Human Perception of Odors and Odor Blockers. The registered enrollment is 27, allocation is listed as NA, and masking is listed as NONE. Participants who smoke were asked to smell odor samples and report on odor pleasantness and desire to smoke.

The primary outcome is the Cigarette Purchase Task, summarized as a mean on a log (US Dollars) scale with standard deviation. The registry describes skewed task data and a transformation after adding 0.01. Odor Pleasantness Score is listed as a secondary outcome. The timeframe is 3 hours (total for all outcome measures).

The record lists 3 outcome measures and 0 analyses. Numerical outcome results, analysis details, missing-data handling, and outcome-specific participant counts are not reported in the registry record. Safety fields report 0 serious adverse events, 0 other adverse events, and 0 deaths among the listed group.