Evaluation of the 755nm Alexandrite for Unwanted Tattoos: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Evaluation of the 755nm Alexandrite for Unwanted Tattoos (NCT01842815), a non-randomized na study. The primary outcome is Tattoo Clearance.

2. Clinical Question

3. Trial Design

This completed study was registered as a non-randomized, parallel-model device study of the 755nm Alexandrite laser. The registry lists an enrollment of 20 and identifies unwanted, non-cosmetic tattoos as the condition. The study’s stated purpose was to collect further safety and efficacy data for tattoo removal, including for recalcitrant tattoos. It was sponsored by Cynosure, Inc. The recorded start was 2013-03, and primary completion was 2015-12.

The two treatment descriptions assign one pass to the right side of the tattoo and two passes to the left side. The double-pass treatment was delivered in the same visit, with the passes 20 minutes apart. The record does not describe random assignment of sides or masking; masking is listed as none. Thus, this is not a randomized, blinded comparison. The registry’s own caution is that the arms are not a like-for-like control comparison.

The side-by-side arrangement may allow observations from the two sides of a tattoo to be considered within the same participant, but the registry record does not report how the analysis accounted for this structure. The exact number of tattoos, the number of participants contributing to each outcome, and whether all enrolled participants received both treatments are not reported in the registry record. The record also does not describe allocation procedures beyond the stated side assignments.

Although the record marks the study as completed and lists three outcome measures and three analyses, it does not report the primary outcome results or identify the full set of analysis methods. Study completion and outcome registration alone do not indicate what the comparison found. The available information supports describing the planned treatment contrast and study structure, but not estimating which approach had greater clearance or how certain such an estimate would be.

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 subjects are enrolled in both study arms because all subjects will be receiving treatment on the left side of the tattoo and treatment on the right side of the tattoo in each visit.

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.

Population: 1 subject withdrew, per sponsor request, due to multiple laser devices already used on treatment area. They withdrew before baseline information was taken of them.

6. Primary Endpoint

The registry lists the primary outcome as Tattoo Clearance, measured over Post Treatment 1 (6 Weeks Post Baseline).

The primary endpoint is tattoo clearance, recorded as a score on a scale. The registry describes a clearance aesthetic improvement scale ranging from 0 to 10: 0 represents 0% of the tattoo cleared compared with baseline, while 10 represents 100% cleared compared with baseline. The measure is therefore intended to express the degree of visible clearance relative to the tattoo’s baseline appearance.

The primary assessment time is Post Treatment 1 (6 Weeks Post Baseline). This defines when the clearance score was to be assessed; it does not, by itself, establish how long any change persisted. The registry record does not report the actual scores, the number of observations contributing to the endpoint, or a comparison between the single-pass and double-pass sides.

Using a scale can capture gradations in appearance rather than reducing the assessment to a cleared/not-cleared classification. As a general statistical point, a mean score describes the average recorded scale value, while a standard deviation describes how much individual values vary around that average. Neither is reported for this endpoint in the registry record. A scale score also depends on how the assessment is performed; the record does not report details about assessor training, reliability, or whether assessment was blinded. Those omissions limit interpretation of how consistently the endpoint was measured.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Outcome scale and summary statistics

The registry specifies a continuous primary outcome summarized by a mean and standard deviation. The clearance score runs from 0 to 10, with the endpoints defined in terms of the percentage of the baseline tattoo cleared. A mean is the arithmetic average of recorded scores. A standard deviation describes the spread of scores around that average; it is not the uncertainty in the mean and is not a measure of the treatment contrast by itself.

General statistical explanation: a comparison of means needs both an estimate of the contrast and information about its uncertainty. A confidence interval combines those elements and indicates which contrast values are reasonably compatible with the observations under the analysis assumptions. A narrow interval indicates greater precision than a wide interval, but neither the estimate nor an interval is reported for this endpoint in the registry record. The registry also does not report the arm-specific means or standard deviations.

Structure of the comparison

The treatment sides are specified rather than randomly assigned: the right side received one pass and the left side received two passes, with the second pass 20 minutes after the first. Although the record describes a parallel model, this side-based setup raises a question about whether observations are paired within participants. General statistical explanation: when two measurements come from the same person or tattoo, they may be related. An analysis that treats related measurements as independent can misstate uncertainty. A paired analysis instead uses the within-unit relationship. The registry record does not report whether the outcome analysis used a paired approach, whether multiple tattoos contributed per participant, or how dependence was handled.

Non-randomized assignment also affects interpretation. General statistical explanation: random allocation is used to reduce systematic differences between treatment groups, on average. When treatment is assigned by side without randomization, side-related features and other differences may be entangled with the treatment contrast. A statistical adjustment can address measured characteristics under suitable assumptions, but cannot guarantee removal of unmeasured differences. The registry record does not report adjustment variables or an adjusted primary analysis. Masking is listed as none, and the record does not explain whether the person assessing clearance knew which side received which treatment.

Uncertainty, testing, and assumptions

The registry record does not report a confidence interval or a p-value for tattoo clearance. General statistical explanation: a p-value is interpreted relative to a specified statistical model and null hypothesis. It is not a measure of the size or importance of a difference. A confidence interval is generally more informative about precision because it displays a range of plausible values for the contrast under the method’s assumptions. Neither can be reconstructed from the endpoint definition alone.

The study record lists three outcome measures and three analyses, but the analysis methods and any testing hierarchy are not reported in the registry record. General statistical explanation: when several outcomes or comparisons are tested, the chance of at least one apparently unusual result can increase if the tests are interpreted without accounting for multiplicity. Possible approaches include identifying one primary test in advance or adjusting inference across a family of tests. The record does not state whether a multiplicity approach was planned or used.

The registry’s planning description for sample-size illustrations refers to a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect defined as a stated fraction of the observed effect. It also distinguishes calculations expressed as participants per arm from time-to-event calculations expressed as total events. These are planning assumptions for an illustration, not evidence of the study’s original design justification, and they do not constitute observed power. The registry record does not report the trial’s own sample-size justification. The observed primary effect needed to interpret such an illustration is not reported in the registry record.

Distribution and variability

General statistical explanation: methods for comparing means rely on assumptions about the observations and their variability. A scale bounded at 0 and 10 cannot take values outside those limits, and scores may not be distributed symmetrically or evenly across the scale. The appropriateness of a particular model depends on the actual score distribution, the analysis unit, and the relationship between paired observations. Those data and diagnostics are not reported in the registry record, so the fit of any particular method cannot be assessed.

If outcomes were analyzed as a mean, it would be useful to know whether the analysis accounted for the scale’s bounds and the study’s side-based structure. If outcomes were analyzed by another method, the method and its estimand would need to be stated to interpret its result. The registry record does not report these details. Thus, the endpoint description identifies what was intended to be measured, but does not establish which inferential method generated a result.

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("755nm Alexandrite Laser Single Pass (Right Side).", "755nm Alexandrite Laser Double Pass (Left Side)")
n   <- c(19, 19)
m   <- c(2.875, 4.25)
sp  <- c(2.112, 2.513)
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  755nm Alexandrite Laser Single Pass (Right Side).  19  2.875  2.112  1.857  3.893
CARM  755nm Alexandrite Laser Double Pass (Left Side)  19  4.250  2.513  3.039  5.461

11. Multiplicity, Missing Data and Analysis Populations

The registry lists three outcome measures and three analyses. It does not report the full outcome list and analysis details in this record, nor does it state whether a prespecified testing hierarchy or multiplicity adjustment was used. General statistical explanation: when multiple outcomes or contrasts are tested, unadjusted interpretation can make chance findings more likely across the set. A prespecified primary outcome can help focus interpretation, but a label of primary outcome does not tell readers whether other tests were adjusted for or how they were interpreted.

The primary endpoint is identified as tattoo clearance at Post Treatment 1 (6 Weeks Post Baseline). The registry record does not report outcome results, the number of participants with observed values, or the analysis population. It also does not report how missing outcome values were handled, whether any participants were excluded from analysis, or whether the analysis followed an intention-to-treat or other defined approach.

General statistical explanation: missing outcomes can affect both the estimated treatment contrast and its uncertainty, particularly if the likelihood of missingness is related to treatment or outcome. The number missing and the reasons for missingness help readers assess this possibility, but those details are not reported in the registry record. Without the results and analysis-population information, the completeness and robustness of the primary comparison cannot be evaluated.

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.

Most frequent non-serious adverse event terms

The registry reports safety figures for the 755nm Alexandrite Laser group. Serious adverse events affected 0 of 20 participants at risk, and deaths were 0. Other adverse events affected 4 of 20 participants at risk. The record does not list any top serious adverse event terms.

These are counts of participants affected as recorded in the registry, not a detailed description of event severity, timing, duration, or relationship to treatment. The figures do not show how many total event episodes occurred, whether the same participant experienced more than one event, or the criteria used to classify events. Those details are not reported in the registry record.

General statistical explanation: a count of zero serious events in a group does not establish that the risk is zero; estimates from small groups can be imprecise. In addition, there is no randomized control group in this non-randomized comparison, so the figures do not provide a like-for-like estimate of safety relative to an untreated or alternative-treatment group. These registry counts describe what was recorded for the group, but cannot by themselves establish whether an event was caused by the laser or compare safety between the one-pass and two-pass approaches.

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

The record establishes that the study evaluated a 755nm Alexandrite laser for unwanted, non-cosmetic tattoos, including recalcitrant tattoos, and compared a single pass on the right side with two passes on the left side. It specifies tattoo clearance as the primary outcome and defines a score scale from 0 to 10, assessed at Post Treatment 1 (6 Weeks Post Baseline). It also records enrollment of 20 and safety counts for the laser group.

Those details describe the study question and measurement plan, but the primary clearance results are not reported in the registry record. There are no arm-specific scores, estimated contrast, confidence interval, or p-value to interpret. Accordingly, the record does not show whether the scores differed, the size of any difference, or the precision of an estimate. It would be inappropriate to infer a result from the study’s completion status, outcome definition, or safety counts.

The comparison also has important design constraints. Treatment assignment was non-randomized, masking was listed as none, and the arms are not a like-for-like control comparison. The side assignment means that treatment and side are linked in the recorded design. The registry record does not explain how the analysis addressed these features or whether the assessment was susceptible to knowledge of treatment.

General statistical explanation: a measured difference in a non-randomized comparison can reflect treatment, baseline differences, measurement processes, or a combination of factors. Statistical adjustment may help with measured differences, but its adequacy depends on what was measured and the model used. Those analysis details are not reported in the registry record.

The stated assessment time concerns clearance at 6 Weeks Post Baseline. It does not establish longer-term results or persistence. Missing-data handling, the number analyzed, and the results of other outcomes are also not reported in the registry record. The justified interpretation is therefore limited: the registry records a specific treatment comparison and endpoint, but does not provide the primary outcome evidence needed to quantify or interpret the clearance contrast.

14. Why This Trial Matters Statistically

This study is statistically interesting because the comparison is built around two treatment sides of a tattoo rather than separately randomized groups. The one-pass treatment is assigned to the right side, while the two-pass treatment is assigned to the left side. That setup makes the analysis unit and the relationship between observations important. If side scores are paired within a participant, the method should account for their dependence; if multiple tattoos contribute, clustering may also matter. The registry record does not report how these features were handled.

The outcome is a bounded clearance scale anchored to the baseline tattoo, with a mean and standard deviation specified as summary measures. General statistical explanation: averages can be useful summaries, but interpretation also depends on score distribution, variability, and how the scale is applied. The record does not report observed score distributions, assessment reliability, or assessor masking. These details matter when judging whether a numerical contrast reflects a consistent difference or is sensitive to measurement choices.

The record also illustrates the distinction between a registered endpoint and an interpretable result. It specifies what was to be measured and when, but does not report the resulting clearance values or uncertainty. Without those, readers cannot assess effect size or precision. Enrollment and completion status cannot substitute for an outcome estimate.

Finally, the listed safety counts provide descriptive information for the laser group, while the design does not offer a randomized, like-for-like safety control. The study’s statistical contribution cannot be fully judged without reported outcomes and analysis methods. Its record nonetheless makes clear why design, outcome reporting, and uncertainty are essential alongside the treatment description.

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 report the primary tattoo-clearance results, including arm-specific means, standard deviations, an estimated contrast, a confidence interval, or a p-value. The primary comparison therefore cannot be quantitatively interpreted. It also does not report results for the other outcome measures.

The study is non-randomized and unmasked. The right side received one pass and the left side received two passes, so treatment and side are linked. The registry record does not report whether side assignment could be influenced by tattoo characteristics, whether assessors knew the treatment, or whether the analysis adjusted for relevant differences. The arms are explicitly not described as a like-for-like control comparison.

Enrollment was 20, but the number contributing primary endpoint data and the analysis population are not reported in the registry record. The number of tattoos per participant, missing observations, reasons for missingness, and methods for handling missing data are also not reported. It is therefore unclear how complete the outcome data were and whether all enrolled participants contributed to the analysis.

The endpoint is a scale-based assessment, but details about who assessed clearance, how the scale was applied, and its reliability are not reported. The stated assessment is at Post Treatment 1 (6 Weeks Post Baseline); the record does not establish longer-term outcomes or durability. The analysis method, model assumptions, and any adjustment for multiple analyses are not reported in the registry record. Together, these gaps limit evaluation of measurement quality, precision, bias, and generalizability.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Evaluation of the 755nm Alexandrite for Unwanted Tattoos — NCT01842815.
• Registry record last updated 2021-01-05; status last verified 2020-12.
• Results first posted 2021-01-05.
• 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

NCT01842815 is a completed, non-randomized device study sponsored by Cynosure, Inc., with enrollment of 20. It evaluated a 755nm Alexandrite laser for unwanted, non-cosmetic tattoos, including recalcitrant tattoos. The recorded study start was 2013-03, and primary completion was 2015-12.

The treatment comparison assigned one pass to the tattoo’s right side and two passes to its left side, with the passes 20 minutes apart. Masking was listed as none. The primary endpoint was tattoo clearance on a scale from 0 to 10 at Post Treatment 1 (6 Weeks Post Baseline), summarized as a mean and standard deviation.

The registry record does not report primary endpoint results, analysis details, missing-data methods, or the number included in the primary analysis. Safety figures list 0 serious adverse events among 20 at risk, 0 deaths, and other adverse events affecting 4 of 20 at risk. The record cautions that the arms are not a like-for-like control comparison.