Interventional Study to Evaluate the Appearance of Surgical Scars After Laser Therapy: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Interventional Study to Evaluate the Appearance of Surgical Scars After Laser Therapy (NCT02985151), a randomized na study. The primary outcome is Change in Vectra Measured Length V1 (Month 0)-V2 (Month 3) for Original Group; Visit 3 (Month 6) to Visit 4 (Month 9) for Crossover Group.

2. Clinical Question

3. Trial Design

The registry describes a completed, single-center, randomized, triple-masked, placebo-controlled study with a crossover model. The study evaluated fractional carbon dioxide laser treatment for surgical scars of the face and neck over a period described as up to 12 months. The registry lists the study as completed, with a start date of 2016-11-01 and primary completion date of 2020-12-01.

Participants were randomly assigned to a higher- or lower-energy laser treatment. The high-energy group received the laser in Mid or Deep mode, while the low-energy placebo group received Light mode. The registry says that subjects and raters were blinded to the therapy level. At visits, scars were photographed, participants completed a questionnaire, and three physicians evaluated scars: one in person and two using photographs. Treatment visits included instructions and a diary for recording skin changes such as redness, swelling, pain, and itching.

The registry describes visits every three months for up to 12 months. During the first three visits, participants received their assigned treatment. At the third visit, participants could choose additional treatment or end participation. For those continuing, the fourth visit was a treatment visit for one group and the fifth visit was for data collection without treatment. The primary outcome compares change from month 0 to month 3 for the original group, and from month 6 to month 9 for the crossover group.

The primary outcome population is described as including the 25 participants originally randomized to high-energy treatment and 10 crossover subjects in the high-energy group. The low-energy placebo group includes 25 participants who did not withdraw; the registry notes that 26 were originally randomized and one withdrew. These descriptions make clear that the primary analysis incorporates crossover data as well as the initial assignment. Further details of the trial’s original analysis plan are 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.

Before assignment: 51 patients enrolled in the study. One subject withdrew from the study prior to treatment. A total of 50 subjects received treatment in the study. There were 10 subjects who crossed-over from low-energy treatment to high-energy treatment after completing the low-energy portion of the study.

Original Randomization

Reasons for not completing this period:

Crossover From Low to High Energy

Analysis population for the primary outcome, as defined in the registry: The high-energy treatment group includes the 25 participants originally randomized to high-energy treatment and the 10 crossover subjects. The low-energy placebo group includes the 25 subjects who did not withdraw from the study (26 were originally randomized, and one withdrew).

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 Change in Vectra Measured Length V1 (Month 0)-V2 (Month 3) for Original Group; Visit 3 (Month 6) to Visit 4 (Month 9) for Crossover Group, measured over 3 months (month 0-3 for original randomized group, month 6-9 for crossover group).

The primary endpoint is the mean change in scar length measured with the Vectra microtopographic imaging system. The registry specifies millimeters as the unit and a standard deviation as the measure of spread. The assessment interval is three months: month 0 to month 3 for the original randomized group, and month 6 to month 9 for the crossover group. The endpoint description says the study team used Vectra imaging to measure changes in scar length after laser therapy.

Scar length is a continuous measurement: it can take a range of values rather than being limited to categories such as improved or not improved. Comparing mean changes therefore describes the average measured change in each group, while the standard deviations describe how much individual measurements vary around those means. The reported mean changes are 0.1 mm for the high-energy group and 0.03 mm for the low-energy placebo group.

Using an imaging-based measurement offers a defined way to quantify scar length across assessments. The registry also describes photographs, participant questionnaires, and physician evaluations, but the primary endpoint is specifically the Vectra-measured length change. The registry record does not report the precise measurement procedures, assessor reliability, or how changes in length were coded, including the direction that corresponds to an increase or decrease. Accordingly, the statistical result should be read as a comparison of the posted mean changes, without assigning a clinical meaning to the sign of change beyond what the registry states.

7. Results Posted in the Registry

• High Energy Treatment Group: mean 0.10 versus 0.03 on control; difference 0.07 (95% CI -0.21 to 0.35), standardized effect d = 0.11; z-test p = 0.621.

8. Statistical Interpretation

9. Statistical Methods Explained

For a continuous outcome, a group mean summarizes the average measurement, while the standard deviation describes the spread of measurements around that mean. In the primary comparison, the reported mean changes are 0.1 mm for the high-energy group and 0.03 mm for the low-energy placebo group. Their reported standard deviations are 0.78 mm and 0.26 mm, respectively. A mean difference expresses the contrast between these two means; the posted difference is 0.07 mm, with high-energy treatment as the group being compared against low-energy treatment.

What does the mean difference represent?

The mean difference is expressed in the outcome’s original unit, millimeters. A positive estimate means that the high-energy group’s posted mean change is numerically greater than the low-energy group’s posted mean change, according to the comparison’s stated ordering. That arithmetic direction should not be equated with improvement or worsening because the registry record does not specify how the direction of length change maps to clinical benefit. The estimate is an average contrast and does not imply that every participant had a change of that size.

What does an unadjusted comparison mean?

General statistical explanation: an unadjusted comparison contrasts groups without accounting for other variables in a model. It is a straightforward summary, but it may not address differences in participant characteristics, study timing, or other factors. The posted comparison is identified as unadjusted. The registry record does not report an adjusted model or the original statistical analysis plan, so it is not possible to determine whether a different planned analysis was used by the study team.

The reported p-value is 0.621. General statistical explanation: a p-value measures how unusual the observed data, or data more extreme, would be under a specified null model and its assumptions. It is not the probability that the null hypothesis is true, and it does not tell readers the probability that a treatment has an effect. The unadjusted p-value should be interpreted alongside the effect estimate and its confidence interval, not as a stand-alone verdict.

Why does the confidence interval matter?

General statistical explanation: a confidence interval describes a range of effect estimates compatible with the data under the method’s assumptions. Its width reflects precision; a wider interval indicates less precision. The posted interval for the mean difference includes zero. That means a zero difference is among the values compatible with the data, while values on either side of zero are also compatible within the interval. The interval therefore does not establish a difference, but it also does not show that all meaningful differences have been ruled out.

The comparison includes groups with different reported standard deviations. General statistical explanation: when measurements are more variable, the group means tend to be less precise for a given amount of data, making it harder to distinguish a real group contrast from sampling variation. Over-dispersion is a related concept for count data, where observed variability exceeds what a simple model expects; it is not the central issue for this continuous length outcome. Here, the relevant reported feature is the difference in standard deviations, not evidence of a particular cause for that difference.

How does the crossover structure affect interpretation?

The registry describes a crossover model and indicates that the primary population includes the original high-energy group and 10 crossover subjects. The high-energy group outcome population is described as 25 participants originally randomized to high-energy treatment plus crossover subjects. The low-energy placebo group includes 25 participants who did not withdraw, from 26 originally randomized. The compared intervals are month 0 to month 3 for the original group and month 6 to month 9 for crossover subjects. This composition means the posted primary comparison is not simply a comparison of all participants according to their initial random assignment.

General statistical explanation: crossover designs can allow participants to receive more than one treatment condition over time, but interpretation may depend on sequence, timing, and possible carryover effects. The registry record does not report enough detail to assess these issues, nor does it describe the statistical handling of repeated observations. It is therefore appropriate to note the structure without assuming how the analysis addressed it.

The primary outcome is a mean of a continuous measure, and the comparison uses a mean difference. The available results do not include a posted analysis entry, model specification, or detailed missing-data procedure. The recalculated statistics are unadjusted summaries, and no discrepancy between the posted result and recalculation is flagged in the record. They should not be treated as a substitute for any sponsor analysis that may exist outside the registry record.

10. Confidence Intervals and Precision

The reported mean difference in change in scar length is 0.07 mm. Its confidence interval includes zero, and the unadjusted p-value is 0.621. The interval’s inclusion of zero means that the data are compatible with no mean difference under the analysis assumptions. Because it also extends to values on both sides of zero, the result does not settle the direction of the group contrast.

Confidence intervals are useful because they show uncertainty around an estimate rather than presenting only a single point value. General statistical explanation: a confidence interval is constructed using a method that, under its assumptions and repeated use, has a stated coverage property. It is not a range that guarantees the true effect lies inside it, nor does it assign probabilities to individual values after the data have been observed. Its width is an indication of precision: narrower intervals generally indicate more precise estimates, while wider intervals leave a broader range of effects compatible with the data.

The group standard deviations were 0.78 mm and 0.26 mm, indicating different amounts of observed spread in the two groups. The registry reports group sizes for the primary comparison as 35 and 25, but the population description shows that the high-energy group includes crossover subjects and the low-energy group excludes one withdrawal. These details are relevant to how the comparison was assembled and to how much information the estimate contains.

The registry record does not report a clinically important difference threshold for scar length. Without such a threshold, the interval cannot be judged against a stated boundary for a clinically meaningful effect. The posted statistics support describing the estimate as uncertain; they do not justify interpreting the result as proof that the groups are equivalent or that any possible difference is unimportant.

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 sample-size figures are planning illustrations based on the observed effect, not counts from this completed study. For this continuous outcome, the figures are participants per arm, not total events. The assumptions stated for the illustration are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is set to the stated fraction of the observed effect. The registry record does not report the trial’s original sample-size assumptions or justification.

The 80% power column gives the planned number of participants per arm for a hypothetical study designed to have an 80% chance of detecting the specified effect if that effect were the true one, under the listed assumptions. The 90% power column describes the corresponding hypothetical planning target for a 90% chance. These are design calculations, not properties measured after the trial. This is not observed power.

The rows consider planning for 100%, 75%, and 50% of the observed effect. The posted figures are 1,233 and 1,650 participants per arm for 100% of the observed effect; 2,191 and 2,933 for 75%; and 4,929 and 6,599 for 50%, for 80% and 90% power respectively. The figures increase as the effect to be detected becomes smaller, because smaller differences are harder to distinguish from random variation. The higher power target also requires a larger planned sample under the stated assumptions.

These calculations use the observed estimate as their starting point. The estimate itself is uncertain, as reflected by a confidence interval that includes zero, so the illustrations should not be read as a definitive prescription for a future study. The registry does not report the assumptions used for the original trial design, and these planning figures do not reveal whether the completed study met any original target.

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, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = 0.070; pooled standard deviation σ = 0.620.
2. n = 2 × (1.96 + 0.842)² × 0.620² / 0.070² = 1,232.2, rounded up to 1,233 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
delta <- 0.07                      # observed difference in means
sigma <- 0.620177949991107                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^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 (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(2985151)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 1,233 (80% power), 1,650 (90% power)
 75% of observed effect: n per arm = 2,191 (80% power), 2,933 (90% power)
 50% of observed effect: n per arm = 4,929 (80% power), 6,599 (90% power)
power.t.test: 1233.1 
Simulated power at n = 1,233 per arm: 0.800 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-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 lists 11 outcome measures and one posted secondary outcome. It identifies tolerability associated with laser treatment at specified visits for the original and crossover groups. The primary outcome is the change in Vectra-measured scar length. Although multiple outcome measures are listed, the registry record does not report a multiplicity adjustment, a hierarchy for testing outcomes, or a detailed plan for controlling false-positive findings across analyses.

General statistical explanation: when several outcomes or comparisons are tested, the chance of obtaining at least one apparently notable result can rise unless the analysis plan accounts for multiple testing. An adjustment or prespecified testing hierarchy can address that issue, but the registry does not say whether one was planned or used. The single posted unadjusted p-value should therefore be read as the result for its particular comparison, not as evidence that all outcomes were evaluated under a reported multiplicity strategy.

The record reports enrollment and gives population descriptions for the primary outcome, including one withdrawal from the initially randomized low-energy group and crossover participants in the high-energy analysis population. It does not report a complete participant flow, reasons for withdrawal, missing outcome counts by visit, or the method used to handle missing measurements. It also does not report whether the primary comparison followed an intention-to-treat population, a per-protocol population, or another prespecified analysis population.

These omissions matter because missing outcome data can affect both the number of observations contributing to a comparison and the assumptions needed to interpret it. General statistical explanation: analyses that exclude missing observations may be biased if the probability of missingness is related to outcome values or treatment experience. Different missing-data methods rely on different assumptions. No particular missing-data mechanism or method can be inferred from the posted record.

The registry gives the primary outcome population in descriptive terms, but does not report a full statistical analysis plan, model details, or analysis entries. Consequently, the available record does not establish how repeated measurements, crossover timing, missing data, or multiple outcomes were handled in the sponsor’s analysis.

14. 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 serious adverse events for the high-energy treatment group among 35 at risk and for the low-energy placebo group among 26 at risk. The serious adverse event count was 0 in each group. Deaths were also reported as 0 in each group. The registry lists no top serious adverse event terms.

Other adverse events were reported in both groups: 7 among 35 at risk in the high-energy group and 7 among 26 at risk in the low-energy group. These are counts, not a comparison adjusted for time exposed or other participant characteristics. The safety figures should be read using their stated at-risk groups; they differ from the primary outcome population description for the low-energy group, which identifies 25 participants who did not withdraw.

A zero serious adverse event count means that none were reported in the registry’s stated groups. It does not establish that no such event could occur, and it does not by itself determine whether the groups have the same safety profile. The record does not provide event descriptions for the other adverse events, severity or relatedness details, exposure-adjusted rates, or a more extensive safety analysis. These figures therefore describe the posted counts, not a complete assessment of safety.

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

The posted result is a comparison of mean change in Vectra-measured scar length over specified three-month intervals. The high-energy group’s mean change was 0.1 mm, compared with 0.03 mm in the low-energy placebo group. The reported mean difference was 0.07 mm, with an unadjusted p-value of 0.621 and a confidence interval that includes zero. The data do not establish a clear difference between the groups on this endpoint.

That interpretation is not the same as concluding that the treatments are equivalent. Equivalence requires a prespecified margin defining how small a difference must be to count as practically equivalent, together with an analysis designed to assess that question. The registry record does not report such a margin or an equivalence analysis. Nor does a result that does not establish a clear difference prove that no effect exists; the confidence interval indicates uncertainty around the estimate.

The endpoint is scar length, not a complete measure of appearance or experience. The study description also mentions participant questionnaires, physician ratings, photographs, and tolerability, but the primary result does not summarize all of those measures. The record lists a tolerability outcome among secondary outcomes, but does not provide a posted secondary result in the available analysis information. The primary result should therefore not be generalized to outcomes it does not measure.

The crossover structure also limits a simple interpretation of the result as a comparison of only the original randomized groups. The high-energy primary population includes crossover subjects, and the outcome intervals differ for the original and crossover groups. The registry record does not report the detailed model or handling of timing and repeated measurements. Those limitations do not invalidate the posted summary, but they define what can be concluded from it.

In short, the registry reports a small positive mean contrast in the stated ordering, with uncertainty that includes no difference. The result is descriptive and imprecise. It does not establish benefit, lack of benefit, equivalence, or a conclusion about every aspect of surgical scar appearance.

16. Why This Trial Matters Statistically

This study illustrates why a randomized design and a clear endpoint do not, by themselves, remove the need to examine the analysis population and uncertainty. The primary outcome is a defined continuous measurement of scar length, and random assignment was used for the initial treatment comparison. Yet the posted primary population includes crossover participants and uses different three-month intervals for the original and crossover groups. Understanding those features is essential to interpreting the result as a group contrast.

The point estimate alone could invite an overly simple reading. The mean difference is 0.07 mm, but the confidence interval includes zero and the unadjusted p-value is 0.621. Together, these statistics show why an estimate should be interpreted alongside its precision. A point estimate is not a guarantee of the true effect, and a non-significant comparison is not proof of equality.

The differing standard deviations also matter. The group measurements show different observed variability, which can affect how precisely group means and their contrast are estimated. The registry record does not provide enough detail to explain that difference or to assess the measurement process, so it is important not to attribute it to a particular cause.

Finally, registry reporting helps distinguish what is known from what remains unclear. The record describes the treatment settings, masking, visits, and primary outcome, but does not report the original statistical plan, detailed missing-data methods, or a multiplicity strategy. For biostatisticians and clinical researchers, this is a reminder to read outcome results in the context of design, population definition, measurement timing, and reporting completeness—not just the p-value.

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 primary comparison combines the original high-energy group with crossover subjects, while the low-energy group consists of participants who did not withdraw. The registry gives the high-energy outcome population as 25 originally randomized participants plus 10 crossover subjects, and describes 25 low-energy participants as remaining from 26 originally randomized. The comparison therefore does not represent only the original randomized groups. The primary outcome uses month 0 to month 3 for the original group and month 6 to month 9 for crossover participants.

The registry record does not report the statistical model used for the primary analysis, how any repeated measurements were handled, or how crossover timing was incorporated. It also does not report the original statistical analysis plan, the trial’s original sample-size justification, missing-data methods, or a multiplicity strategy. These gaps restrict assessment of whether the posted unadjusted comparison reflects the planned analysis.

The available outcome summary reports means and standard deviations but not participant-level data or detailed baseline characteristics. The record does not explain the direction of change in clinical terms, provide a threshold for a clinically important difference, or report measurement reliability. Consequently, the clinical importance of the estimated difference cannot be determined from the primary endpoint summary alone.

The safety record gives event counts but does not describe the other adverse events in detail, their severity or relatedness, or exposure-adjusted comparisons. The registry lists multiple outcomes, but the available analysis information does not provide results for all of them. These limitations mean that interpretation should remain focused on the posted primary outcome comparison and the specific safety counts rather than extending to broader conclusions about appearance, tolerability, or safety.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Interventional Study to Evaluate the Appearance of Surgical Scars After Laser Therapy — NCT02985151.
• Registry record last updated 2023-06-06; status last verified 2023-06.
• Results first posted 2023-06-06.
• 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

The registry describes a completed, single-center, randomized, triple-masked, placebo-controlled crossover study of fractional carbon dioxide laser treatment for surgical scars of the face and neck. Enrollment was 51. The primary outcome was mean change in Vectra-measured scar length, in millimeters, over a three-month interval.

The posted means were 0.1 mm for the high-energy treatment group and 0.03 mm for the low-energy placebo group, with a mean difference of 0.07 mm. The unadjusted p-value was 0.621, and the confidence interval includes zero. The primary comparison includes crossover subjects and uses different stated intervals for the original and crossover groups. The registry record does not report the original analysis plan, missing-data methods, or a multiplicity strategy.

Serious adverse events and deaths were reported as 0 in both stated safety groups. Other adverse events were reported as 7 in each group. These figures describe the registry counts and do not constitute a complete safety analysis.