A Study to Evaluate the Efficacy and Safety of a Leave-in Spray in Subjects With Head Lice Infestation: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study to Evaluate the Efficacy and Safety of a Leave-in Spray in Subjects With Head Lice Infestation (NCT05565820), a randomized phase 4 study. The primary outcome is Proportion of Participants Who Are Completely Free of Live Lice.

2. Clinical Question

3. Trial Design

The registry record describes a Phase 4, randomized, parallel-group study with no masking. It lists an enrollment of 58 and a completed status. The study title describes a prospective, randomized controlled study in the community, and the brief summary frames the comparison as Vamousse Spray 'n' Go versus a 1% permethrin control shampoo for head lice.

The named intervention groups are Vamousse Spray 'n' Go and Nix Creme Rinse Lice Treatment. The record’s brief summary calls the comparator a 1% permethrin control shampoo, while the intervention listing and arm description use the Nix name and describe a 1% permethrin lotion. These descriptions indicate the intended active comparison, but their wording is not identical. The record’s available description says clinical staff applied Vamousse at the baseline visit and left it on for 8 hours. For the comparator, it describes baseline hair preparation before treatment. Full application details for both arms are not available in the registry record.

Randomization means assignment was intended to allocate participants to study groups by chance, but the allocation sequence method and any concealment procedures are not reported in the registry record. “No masking” means the study is listed as unmasked; the record does not specify which people knew each participant’s assigned treatment. The parallel design means the groups were followed as separate treatment arms rather than participants crossing between treatments.

The study started on 2022-12-15 and had a primary completion date of 2023-03-12. The record lists two outcome measures and six analyses, but does not provide the statistical analysis plan, the analysis methods, or numerical primary-outcome results in the registry record for this analysis. Therefore, the design can be described, but the comparative effect and the method used to estimate it cannot be reconstructed from the registry record.

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.

2 Day Treatment Effectiveness

7 Day Treatment Effectiveness

Reasons for not completing this period:

14 Day Treatment Effectiveness

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: The 58 subjects who completed one or more of the three post-baseline 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.

Population: The pattern of infestation levels of the primary participant in each household and the sizes of the households that were encountered in the sequential enrollment process resulted in an imbalance between the numbers of participants in the two treatment groups by the time that the study total of 58 participants was reached. Resources did not permit further enlargement of the sample to reduce this imbalance, but the power of the study to detect the difference that occurred remained high at .95.

6. Primary Endpoint

The registry lists the primary outcome as Proportion of Participants Who Are Completely Free of Live Lice, measured over 2, 7, and 14 days from baseline.

The primary endpoint is the proportion of participants completely free of live lice at Days 2, 7, and 14 from baseline. The definition is based on examination for live adult lice and nymph lice: a participant counts as lice-free only when neither is present. The registry record states that zero subjects in each group were lice-free at baseline.

This endpoint expresses the outcome as a proportion rather than relying on raw counts of lice-free participants. The record explains that the groups differed substantially in size and that the numbers of lice-free participants were transformed into proportions of the respective group totals on the respective assessment days. In general, expressing outcomes as proportions can make group results more comparable when group sizes differ, because the measure accounts for the size of each group.

Assessing the endpoint at several post-baseline times allows the record to describe lice-free status at different points after treatment. The record does not report the actual proportions or counts for Days 2, 7, or 14, nor does it identify a single time point as the sole comparison for interpretation. Without those results, the direction, size, and precision of any group difference cannot be assessed from the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry information identifies the endpoint and study structure, but it does not report the statistical tests or models used for the primary analysis. The concepts below are general explanations of how such data can be analyzed; they are not claims about the method used in this study.

What does a proportion measure?

A proportion is the number of participants meeting a defined condition divided by the relevant group total. For this endpoint, the condition is being completely free of live adult and nymph lice. The registry record says that the group counts were transformed into proportions using each group’s participant total on the respective assessment days. This makes the result interpretable as the share of the group meeting the endpoint, rather than just a raw count that depends on group size.

Proportions still depend on having a clearly defined denominator. If some participants do not have an assessment at a particular time, the denominator may differ from the number originally assigned to that group. The record describes the primary population as subjects who completed one or more post-baseline assessments, but does not report the denominator used at each time point or how missing assessments were handled. Those details matter when comparing proportions.

How can groups be compared?

In general, a comparison of two proportions can be reported as a difference, a ratio, or another model-based contrast. Each form answers a somewhat different question. A difference describes the absolute separation between proportions, while a ratio describes their relative size. A confidence interval gives a range of values compatible with the observed data under the assumptions of the analysis; it conveys precision as well as direction. A p-value, when used, summarizes how unusual the data would be under a specified null hypothesis and model. None of these primary-outcome estimates or inferential statistics are reported in the registry record.

Different statistical methods can account for the outcome’s binary nature and for the study structure. For example, a model could estimate a group contrast at each assessment or account for repeated observations from the same participant. These are general possibilities only. The record does not identify a model, test, covariate adjustment, or method for handling within-participant correlation. It would be inappropriate to attribute any particular method to the investigators.

Why do multiple assessment times matter?

The endpoint is assessed at Days 2, 7, and 14. These are related measurements because the same participant may contribute information at more than one time. Treating each time point as an independent, unrelated question can fail to reflect that connection. A repeated-measures method can, in general, account for the correlation among a participant’s observations, but the registry record does not say whether such a method was used.

Multiple time points also create multiple opportunities to observe a difference. If a study tests several comparisons, the chance of at least one apparently notable result can increase unless the analysis plan addresses multiplicity. Statistical approaches may use an adjustment, a pre-specified testing order, or a clearly designated primary comparison. The registry record does not report whether any such approach was planned or applied, and it does not identify one of the listed time points as the sole primary comparison.

What does randomization contribute?

Randomization is intended to make treatment assignment independent of measured and unmeasured participant characteristics on average. It supports a causal comparison when assignment and follow-up are conducted appropriately, but does not guarantee that groups are identical or remove every source of bias. The record lists the trial as randomized, but does not report the sequence-generation method, allocation concealment, or analysis population details. Those omissions limit assessment of how randomization was implemented and incorporated into the analysis.

The study is also listed as unmasked. In general, knowledge of assigned treatment may influence participant reports, clinical decisions, or outcome assessment, depending on how outcomes are collected. The endpoint involves the presence or absence of live lice, but the record does not describe who assessed it or whether assessment procedures reduced the risk of observer influence. This is a design consideration, not evidence that an assessment bias occurred.

How should planning calculations be read?

In general, a sample-size calculation is a planning exercise based on assumptions about the effect to detect, variability, allocation, and statistical error rates. It is not an observed treatment effect and is not a measure of the study’s observed power. The registry information describes a planning illustration based on the observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation; the target effect is expressed as a stated fraction of the observed effect. No numerical planning outputs or observed primary-effect estimates are reported in the registry record, so the illustration cannot be evaluated or reproduced from the information available.

Such planning calculations require an effect estimate to anchor the assumed target. If the observed effect is uncertain, a calculation based on it is also uncertain. It should be interpreted as a conditional illustration under its assumptions, not as a guarantee that a future study would achieve a particular result. In this case, the underlying primary-outcome estimates are not reported in the registry record, and the listed primary endpoint spans multiple assessment times rather than a single reported comparison.

What can be concluded about the analysis methods?

The registry record reports the outcome definitions, assessment schedule, design labels, and the existence of analyses, but it does not report the statistical plan, model specifications, handling of missing data, multiplicity procedures, or primary-outcome estimates. General statistical principles can explain why these details matter, but cannot replace the missing trial-specific information. Any interpretation of the comparative effect or its precision would require results and analysis details that are not reported in the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The primary outcome is assessed at Days 2, 7, and 14. The registry record does not identify one assessment as the sole primary comparison, nor does it report how the multiple time points were handled statistically. It also does not state whether comparisons across time points or outcomes were adjusted for multiplicity, prioritized through a testing sequence, or interpreted without adjustment. In general, this matters because conducting several statistical tests can increase the chance of a result that appears notable by chance. The registry record does not provide the information needed to determine whether that issue was addressed.

The record lists two outcome measures and six analyses, including a secondary outcome concerning the proportion of change in the total number of live adult lice and nymphs from baseline. The detailed hypotheses, analysis populations, model specifications, and results for those analyses are not reported in the registry record. The number of listed analyses alone does not establish which comparisons were confirmatory or how they were interpreted.

For the primary outcome, the population is described as the 58 subjects who completed one or more of the three post-baseline assessments. This wording does not show whether every participant contributed to every assessment, how many observations were available at each time point, or whether the analysis followed randomized assignment regardless of treatment received. The registry record does not report a missing-data method, imputation approach, sensitivity analysis, or reasons for missing assessments.

These details affect how robust an estimate may be. If assessment availability is related to outcome or treatment, an analysis restricted to observed assessments may differ from an analysis that accounts for missingness. That is a general statistical concern, not a claim about what occurred in this study. Without the analysis population and missing-data methods, the primary endpoint’s numerical results and their interpretation remain unavailable in the registry record.

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 safety listing reports the groups separately. For Vamousse Spray 'n' Go, 43 participants were at risk for serious adverse events and 0 were reported as affected; 43 were at risk for other adverse events and 0 were reported as affected. For Nix Creme Rinse Lice Treatment, 15 were at risk for serious adverse events and 0 were reported as affected; 15 were at risk for other adverse events and 0 were reported as affected. The record reports 0 deaths in each group.

These are counts in the registry’s safety fields, not estimates of comparative risk with uncertainty intervals. Zero reported events means that no events were recorded in these listings; it does not demonstrate that an event is impossible or that the treatments have identical safety profiles. The record does not provide further information about adverse-event definitions, how events were collected, duration of safety follow-up, completeness of reporting, or whether events were considered related to treatment. The serious-event term listing is empty, so no specific serious-event terms are listed.

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

The registry record establishes a randomized, unmasked comparison of Vamousse Spray 'n' Go with Nix Creme Rinse Lice Treatment for head lice infestation. It defines the primary endpoint as the proportion of participants with no live adult or nymph lice and gives assessment times at Days 2, 7, and 14. It also reports that neither group had lice-free participants at baseline.

That information describes what the study set out to assess, but it is not enough to establish the comparative result. The post-baseline group counts and proportions are not reported in the registry record. Without them, there is no basis to describe the direction or magnitude of a difference. The registry record also does not report a confidence interval or p-value for the primary outcome, so the precision and statistical uncertainty of a comparison cannot be assessed.

The endpoint is a measure of lice-free status at scheduled assessments, not a complete account of every aspect of treatment experience. The record lists a secondary measure of change in total live adult lice and nymphs, but its results are not reported in the registry record. Nor does the available information describe other dimensions such as participant experience or longer-term outcomes beyond the stated assessment schedule.

The safety listing reports no serious adverse events, other adverse events, or deaths in the groups. These counts provide a limited description of recorded events; they do not establish that no harms could occur, or that the treatments are equivalent in safety. Further safety methods and follow-up details are not reported in the registry record.

Accordingly, the registry information supports a description of the question, design, endpoint, and listed safety counts. It does not support a conclusion about which treatment had a better lice-free outcome, the size or precision of a treatment difference, or the full safety comparison. Those conclusions would require numerical efficacy results and additional analysis details that are not reported in the registry record.

13. Why This Trial Matters Statistically

This trial is statistically interesting because its primary outcome is a proportion measured at several times, while the record says the groups differed substantially in size. Reporting proportions based on the respective group totals is a way to make the outcome more interpretable across unequal group sizes. It also makes the choice of denominator important: an assessment-specific proportion can be affected by who was available for assessment at that time, and the registry record does not report those denominators or missing-data procedures.

The assessment schedule raises questions about repeated observations and multiplicity. In general, measurements from the same participant may be related, and separate comparisons at several times can complicate interpretation. A statistical analysis plan can clarify whether the central question concerns a particular time point, a pattern across time, or another planned contrast. Such a plan, and any multiplicity strategy, are not reported in the registry record.

The trial’s randomized, parallel design is a useful structure for comparing groups, while its unmasked status is relevant when considering outcome assessment and other study processes. These design labels do not establish that bias occurred or that randomization was implemented in a particular way. The registry record does not provide the allocation details or assessment procedures needed to examine those issues.

Finally, the registry information describes the outcome but does not report its numerical results. This distinction is essential: a clearly defined endpoint and analysis schedule do not, on their own, establish the observed effect or its precision. The study’s statistical importance for readers therefore lies partly in recognizing what the record can establish and what remains unknown without the posted outcome estimates and analysis details.

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 central limitation for interpreting this study from the registry record is that numerical primary-outcome results are not reported. Although the endpoint definition and its Day 2, 7, and 14 assessment schedule are available, the group counts, proportions, and comparative estimates are not. No confidence interval or p-value for the primary outcome is reported in the registry record.

The record describes the primary population as subjects who completed one or more post-baseline assessments, but does not give assessment-specific denominators or say how missing observations were handled. It is therefore unclear from the available information whether the participants contributing to the endpoint differed across assessment times or how such differences were addressed analytically.

Several statistical details are also absent: the allocation sequence method, allocation concealment, the primary analysis method, the definition of the analysis population, any covariate adjustment, and any approach to repeated measurements. The record does not report whether multiple time points or outcomes were subject to a multiplicity strategy. These omissions limit evaluation of the analysis and its uncertainty.

The study is listed as unmasked, but the registry information does not say who knew treatment assignments or who assessed lice status. This prevents a more detailed appraisal of how awareness of treatment could have affected study procedures. The available arm descriptions also do not give complete application instructions for both groups. Finally, the safety counts are not accompanied by further event definitions, collection methods, or follow-up details. These limitations describe gaps in the registry information and do not establish that a particular bias or safety issue occurred.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: A Study to Evaluate the Efficacy and Safety of a Leave-in Spray in Subjects With Head Lice Infestation — NCT05565820.
• Registry record last updated 2025-02-24; status last verified 2025-02.
• Results first posted 2025-02-24.
• 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 describes a completed, randomized, unmasked, parallel Phase 4 study comparing Vamousse Spray 'n' Go with Nix Creme Rinse Lice Treatment for head lice infestation. Enrollment is listed as 58. The primary endpoint is the proportion of participants completely free of live adult and nymph lice at Days 2, 7, and 14. The primary population is described as subjects who completed one or more post-baseline assessments.

Numerical post-baseline primary-outcome results, comparative estimates, and inferential statistics are not reported in the registry record. The record lists a secondary outcome concerning change in total live adult lice and nymphs. Safety listings report zero serious adverse events, zero other adverse events, and zero deaths in each group. Further details about statistical methods, missing data, multiplicity, and safety assessment are not reported in the registry record.