Efficacy and Safety of Licefreee Spray Against Nix 1% Permethrin: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Efficacy and Safety of Licefreee Spray Against Nix 1% Permethrin (NCT01514513), a randomized na study. The primary outcome is The Proportion Within Each Treatment Group of Subjects Who Have no Live Lice.

2. Clinical Question

The clinical question is a comparison of two active treatments on a binary outcome: each participant either had no live lice at the stated assessment or did not. The outcome description focuses on eradication at a particular follow-up time rather than time until lice clearance, change from baseline, or a continuous measure. The registry record also lists adverse events as a secondary outcome, so the study’s stated scope includes safety as well as efficacy. The primary result is a comparison of the posted group counts and the registry’s reported risk difference. It does not, by itself, describe every possible outcome relevant to treatment choice or establish how the treatments perform outside the people and conditions studied.

3. Trial Design

The record describes a randomized, parallel-group study with no masking. Participants were assigned to Licefreee Spray or Nix Creme Rinse, 1% Permethrin. The phase is listed as NA. The sponsor was South Florida Family Health and Research Centers. The recorded study start was 2011-08, and primary completion was 2011-11; the study status is COMPLETED.

The study enrolled 42 participants. For the primary outcome, the registry posts a denominator of 20 in each group. It reports that 17 participants assigned to Licefreee Spray and 9 assigned to Nix had no live lice 15 days following initial treatment. The record does not explain the relationship between the enrollment number and the outcome denominators, or describe whether the denominators reflect exclusions, missing observations, or another analysis population. Those details are not reported in the registry record.

Random allocation is intended to make treatment groups comparable on average, including with respect to factors that may affect the outcome. It cannot guarantee that groups are identical in a small study. No masking means participants and study personnel were not reported as masked to treatment assignment. For a count-based outcome such as live-lice status, the meaning of masking depends in part on how the outcome was assessed; assessment procedures are not reported in the registry record. Details of the randomization method, allocation concealment, treatment administration, and follow-up procedures are also not reported in the registry record.

The registry lists adverse events as a secondary outcome and posts one secondary outcome. It records two outcome measures and no analysis entries, although it does post a comparative estimate and p-value for the primary outcome. The original statistical plan, including the intended sample size and any planned analysis populations, is not reported in 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.

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 The Proportion Within Each Treatment Group of Subjects Who Have no Live Lice, measured over 15 days.

The primary endpoint is the number of participants in each treatment group who had no live lice 15 days following initial treatment. The registry title describes the outcome as the proportion within each group, while the posted values are counts: 17 of 20 participants for Licefreee Spray and 9 of 20 for Nix Creme Rinse, 1% Permethrin. This is a binary endpoint, because each participant’s status at the assessment is classified as either no live lice or not meeting that condition.

A fixed-time binary endpoint is useful when the clinical question concerns the share of participants reaching a defined state by a stated follow-up. It provides a direct group-level description that can be compared using a risk difference, risk ratio, or odds ratio. The risk difference is especially interpretable as the contrast in the probability of the outcome between treatment groups, expressed on the probability scale.

General: a single assessment time gives a snapshot of status at that time. It does not show when the status was achieved, whether it persisted after the assessment, or how participants fared at other times. Those outcomes are not reported in the registry record. The endpoint’s interpretation also depends on consistent outcome assessment and clear handling of participants whose status is unknown; those procedures are not reported in the registry record.

7. Results Posted in the Registry

• Nix Creme Rinse, 1% Permethrin: 45.0% (9/20) versus 85.0% (17/20) on control; risk difference -40.0 percentage points (95% CI -66.8 to -13.2), risk ratio 0.53 (0.32–0.89); unadjusted two-proportion z-test p = 0.008.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is binary: participants are counted according to whether they had no live lice 15 days after initial treatment. For each arm, the registry reports a number meeting the outcome and a denominator. These counts support a direct comparison of the group risks, where risk means the proportion of participants with the specified outcome during the stated assessment. The reported counts are 17 of 20 for Licefreee Spray and 9 of 20 for Nix Creme Rinse, 1% Permethrin.

What does the risk difference express?

The risk difference subtracts the outcome risk in one group from the outcome risk in the other. The registry reports the contrast as Nix relative to Licefreee Spray: -0.4. A negative value means the observed outcome risk was lower in the compared Nix group than in the Licefreee Spray control group. Unlike a relative measure, a risk difference expresses the contrast on the probability scale, making it a direct description of the absolute difference in the chance of meeting the endpoint. Its direction depends on which group is subtracted from which, so the comparison order is important.

How do the risk ratio and odds ratio differ?

The risk ratio compares the outcome risks between groups by division. A value of 1 represents equal risks; values below or above 1 indicate a lower or higher risk in the compared group, according to the stated group order. The registry reports 0.529, with a confidence interval from 0.315 to 0.889. The odds ratio compares odds rather than risks. Odds are the number meeting the endpoint relative to the number not meeting it. The reported odds ratio is 0.144, with a confidence interval from 0.032 to 0.654. When an outcome is not rare, an odds ratio can be numerically farther from 1 than a risk ratio, so the two should not be treated as interchangeable descriptions.

What does the p-value say?

The unadjusted p-value is 0.008. General: a p-value describes how incompatible the observed data, or data more extreme, would be with a specified null model if that model and the analysis assumptions held. It is not the probability that the null hypothesis is true, and it does not measure the probability that the observed result will recur. The registry record does not report adjustment for multiple comparisons; the p-value should therefore be understood as the posted unadjusted result, not as a multiplicity-adjusted finding.

Why does randomization matter?

Randomization is used to reduce systematic differences between treatment groups at the point of assignment. In expectation, it balances both measured and unmeasured factors, though a small trial can still have imbalances by chance. The record identifies the design as randomized but does not report the sequence-generation method, allocation concealment, or any stratification. Without those details, the assignment process cannot be assessed further. The study was unmasked, so knowledge of treatment assignment could potentially influence care or outcome assessment; the outcome assessment procedures are not reported in the registry record.

What does the parallel design imply?

In a parallel-group design, participants are assigned to one treatment group and outcomes are compared between groups. The registry identifies this as a parallel study. It does not report a crossover or repeated-treatment design. The primary endpoint is measured at a fixed time after initial treatment, rather than as time to an event. A fixed-time comparison does not use information about the exact timing of lice clearance, and such timing is not reported.

The registry posts no analysis entries, but it does report the primary comparison and estimates. It does not identify the exact test or model used to produce the p-value and interval, nor whether any covariate adjustment was used. The reported comparison is presented as unadjusted, and the p-value is explicitly unadjusted. A recalculation from summary statistics would be a separate, simple unadjusted analysis; the reported sponsor analysis takes precedence when a discrepancy exists. The discrepancy indicator is false for this record.

General: statistical inference relies on assumptions about how participants entered the analysis, how outcomes were observed, and how the analysis was specified. A complete report would clarify those matters, along with missing-data handling and the analysis population. These details are not reported in the registry record, so the posted summary estimates should be interpreted with that reporting limitation in mind.

10. Confidence Intervals and Precision

The risk-difference estimate is -0.4, and its reported confidence interval runs from -0.668 to -0.132. The full interval is on the negative side of zero, indicating that the posted estimate and its uncertainty are consistent with a lower probability of no live lice in the Nix group than in the Licefreee Spray group, given the comparison order used by the registry. The interval also indicates that the estimated contrast is not pinned down to a single value.

General: a confidence interval is a range produced by a statistical procedure designed, under its assumptions, to capture the underlying parameter at a stated frequency over repeated applications of that procedure. It is not a range containing a known proportion of individual participant outcomes, and it is not a guarantee that the true value lies inside a particular interval. A narrower interval generally indicates greater statistical precision; a wider interval indicates more uncertainty about the effect’s magnitude.

The registry also reports a risk-ratio interval from 0.315 to 0.889 and an odds-ratio interval from 0.032 to 0.654. Each interval is expressed on its measure’s own scale and should be interpreted using the appropriate reference value: zero for a difference and 1 for a ratio. The risk-difference scale is especially useful for understanding the absolute contrast, while the ratio measures express relative comparisons.

The group denominators are 20 in each arm, so the outcome estimates are based on a limited number of participants. The interval is consequently important alongside the point estimate: the point estimate alone can make the result look more certain than it is. The registry does not report details of the interval method or analysis population. The confidence interval describes statistical uncertainty under the method’s assumptions; it does not account for every possible source of uncertainty, such as unreported assessment procedures or missing-data handling.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total events. The illustration assumes a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. It uses the observed effect as a reference and considers planning for 100% of that observed effect, 75% of the observed effect, and 50% of the observed effect. The trial’s own original design assumptions and sample-size justification are not reported in the registry record.

For each assumed effect, the 80% power column gives the number of participants per arm in a planning scenario designed to have an 80% chance of detecting an effect of that specified size under the stated assumptions, if the effect and assumptions were correct. The 90% power column describes the corresponding planning target for a 90% chance. These are planning concepts, not probabilities that the trial result is true or that a treatment is effective.

The displayed planning figures are 22 participants per arm for 80% power and 28 for 90% power when planning for 100% of the observed effect; 36 and 47 when planning for 75% of the observed effect; and 73 and 97 when planning for 50% of the observed effect. Smaller effects are harder to distinguish from random variation, so they require more participants under otherwise unchanged assumptions.

These values are illustrations calculated from the observed effect, not the original design target for this study. They are not observed power: observed power is not a useful substitute for interpreting the observed estimate and its confidence interval. The curve should be read as a visual expression of how the planning requirement changes with the assumed effect, under the same assumptions.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.850; treatment proportion p₁ = 0.450; average p̄ = 0.650.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.6745 = 1.3221.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.6124 = 0.5154.
4. n = (1.3221 + 0.5154)² / (-0.4000)² = 21.1, rounded up to 22 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
p0 <- 0.85                          # control proportion
p1 <- 0.45                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(1514513)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 22 (80% power), 28 (90% power)
 75% of observed effect: n per arm = 36 (80% power), 47 (90% power)
 50% of observed effect: n per arm = 73 (80% power), 97 (90% power)
power.prop.test: 21.1 
Simulated power at n = 22 per arm: 0.817 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Multiplicity, Missing Data and Analysis Populations

The registry identifies one primary outcome: the number of participants in each group with no live lice 15 days after initial treatment. It also lists adverse events as a secondary outcome and posts one secondary outcome. The record reports two outcome measures in total. It does not report a prespecified hierarchy of outcomes, a multiplicity strategy, or whether other analyses were planned but not posted. Therefore, the reported p-value of 0.008 is an unadjusted result; no correction for testing multiple outcomes or comparisons is reported in the registry record.

Multiplicity matters because repeated testing can increase the chance that at least one result appears statistically significant by chance alone. General: a prespecified approach may control that risk by defining which results are primary, adjusting thresholds, or using another planned procedure. The registry record does not describe such an approach. The single posted primary comparison can be read as the main reported efficacy result, while the record does not establish whether it was the only analysis conducted.

The outcome denominators are 20 in each arm, while enrollment is recorded as 42. The registry record does not explain why these figures differ. It does not report whether any participants lacked outcome data, were excluded, or were omitted for another reason. Missing-data methods and the numbers of participants included in each analysis population are not reported. It is therefore not possible to determine from the record whether the primary result follows an intention-to-treat approach, a per-protocol approach, or another population definition.

General: missing outcome data can affect interpretation if the probability of being observed is related to treatment assignment or outcome status. The impact depends on the amount and pattern of missingness and how it is handled. Because the record does not describe missingness or its treatment, the direction and extent of any effect on the comparison cannot be assessed. No interim analyses or stopping rules are reported in the registry record.

14. Safety Results

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

Other (non-serious) adverse events

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

The serious adverse event figures are 0 of 20 participants in the Licefreee Spray group and 0 of 20 in the Nix Creme Rinse, 1% Permethrin group. The posted figures for other adverse events are also 0 of 20 in each group. The registry’s serious-event listing contains no serious adverse event terms. Death counts are not reported in the registry record.

These figures describe what was posted for the recorded groups and should not be read as proof that no adverse events occurred outside the collection or reporting represented in the registry. The record does not give event definitions, ascertainment procedures, follow-up details for safety, or a breakdown by event type beyond the empty serious-event term listing. It also does not report a comparative statistical analysis of adverse events.

General: when no events are recorded in a small group, uncertainty about the underlying event frequency can remain substantial. A zero count is an observation, not evidence that the true risk is exactly zero. The safety figures are descriptive and do not establish a comprehensive safety comparison between treatments.

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

The posted primary result is a difference between the observed groups at a specific follow-up: 17 of 20 participants assigned to Licefreee Spray had no live lice 15 days following initial treatment, compared with 9 of 20 assigned to Nix Creme Rinse, 1% Permethrin. The registry reports a risk difference of -0.4 for Nix relative to Licefreee Spray, with a 95% confidence interval from -0.668 to -0.132 and an unadjusted p-value of 0.008. These numbers describe the registered comparison and its statistical uncertainty.

The result does not establish that the same difference would occur in every setting or population. The study enrolled 42 participants, and the primary-outcome denominators are 20 per arm; the reason for the difference is not reported in the registry record. The small denominators and the interval both matter when considering precision. The study was unmasked, and details of outcome assessment, randomization procedures, missing-data handling, and the analysis population are not reported in the registry record.

The endpoint concerns whether participants had no live lice at 15 days. It does not report when lice clearance occurred, whether the state continued after the assessment, or outcomes at other times. The record does not establish how the treatments compare on outcomes other than those posted. Adverse-event counts are also limited to the registry’s recorded figures, and safety ascertainment details are not reported.

General: statistical evidence about a group comparison is distinct from a decision for an individual. The posted data should be understood as a result from this particular randomized, open-label study, with the reported methods and reporting gaps. They do not, by themselves, settle questions about broader effectiveness, longer-term outcomes, or the full safety profile.

16. Why This Trial Matters Statistically

This trial illustrates several important features of interpreting a binary clinical outcome. The primary endpoint has a clear clinical form—whether a participant had no live lice at a fixed follow-up—and the group counts make the observed outcome understandable. The risk difference expresses the comparison on an absolute scale, while the risk ratio and odds ratio provide relative scales. Reading these measures together helps distinguish different ways of describing the same underlying comparison.

The confidence interval adds information that a single point estimate cannot. The registry’s risk-difference estimate is -0.4, with a 95% confidence interval from -0.668 to -0.132. The interval conveys uncertainty about the magnitude, even though it does not include zero. A p-value alone would not communicate this range, nor would it show how much uncertainty remains about the effect size.

The record also highlights why design and reporting details matter. Randomization is relevant to the credibility of a treatment comparison, but the record does not describe how the assignment sequence was generated or concealed. The study was unmasked, and assessment procedures are not reported. The enrollment number and outcome denominators are distinct, without an explanation of the difference. These omissions limit assessment of how the posted estimates relate to all enrolled participants.

Finally, planning calculations based on an observed effect can be useful for illustrating how sample size changes when a smaller target effect is considered. They are not a substitute for the trial’s original sample-size justification, which is not reported. They are also not observed power. Keeping those planning illustrations separate from the study’s actual design and results is essential for sound interpretation.

17. 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 offers limited detail on methods beyond randomization, parallel allocation, and no masking. The method used to generate the random assignment sequence, conceal allocation, and maintain treatment adherence is not reported. The process for assessing live lice and the identity or masking status of assessors are also not reported. These omissions make it difficult to evaluate potential sources of bias in the primary outcome.

Enrollment is recorded as 42, whereas the primary outcome is posted with 20 participants in each arm. The registry record does not explain the relationship between enrollment and those outcome denominators. It does not report participant flow, reasons for any exclusions, missing outcomes, or whether the analysis included all randomized participants. The analysis population and missing-data approach are not reported.

The study was unmasked, and the primary endpoint was assessed at 15 days. Results at later times, time to clearance, recurrence, or durability are not reported in the registry record. The record posts an unadjusted p-value but does not identify the exact statistical test or model, report covariate adjustment details, or describe any multiplicity approach. The original sample-size justification, interim analyses, and prespecified analysis plan are not reported.

The safety record lists no serious or other adverse events in either group, but event definitions, collection methods, and detailed safety follow-up are not reported. Death counts are not reported in the registry record. With these reporting limits, the posted safety counts should be treated as descriptive rather than a complete assessment of comparative safety. These limitations do not change the reported counts or estimates, but they restrict how fully the study’s conduct and broader applicability can be judged.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Efficacy and Safety of Licefreee Spray Against Nix 1% Permethrin — NCT01514513.
• Registry record last updated 2015-01-01; status last verified 2014-12.
• Results first posted 2015-01-01.
• 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.

21. Record Summary

NCT01514513 is a completed, randomized, parallel-group, unmasked study comparing Licefreee Spray with Nix Creme Rinse, 1% Permethrin, in individuals with head lice. The phase is listed as NA. Enrollment was 42, with primary outcome counts posted for 20 participants in each arm. The primary endpoint was no live lice 15 days following initial treatment.

The registry reports 17 participants meeting the endpoint in the Licefreee Spray group and 9 in the Nix group. The risk difference for Nix relative to Licefreee Spray was -0.4, with a 95% confidence interval from -0.668 to -0.132 and an unadjusted p-value of 0.008. Serious and other adverse event counts were zero in both groups; death counts are not reported in the registry record.

The study sponsor was South Florida Family Health and Research Centers. The recorded study start was 2011-08, and primary completion was 2011-11. Further details about participant flow, analysis populations, missing data, and the original statistical plan are not reported in the registry record.