Using MC1R Genotype to Impact Melanoma Risk Behavior: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Using MC1R Genotype to Impact Melanoma Risk Behavior (NCT03509467), a randomized na study. The primary outcome is Weekday Sun Exposure - NHW - Baseline.

2. Clinical Question

3. Trial Design

This was a randomized, parallel-group behavioral study with no masking. The registry lists the study as completed and records enrollment of 2054 participants. Its stated purpose was to examine how different messages about melanoma risk might affect protective behavior. The intervention involved personalized information, while the control involved standard information; both were described in relation to protection for participants and their children. MC1R genotype determination was also part of the study.

The arm descriptions separate participants by population and MC1R risk category, with intervention and control assignments in each group. The numerical primary results available for interpretation concern the Non-Hispanic White Population and report average-risk control, average-risk intervention, higher-risk control, and higher-risk intervention groups. The registry record does not report numerical primary results for the Hispanic groups. The listed primary outcome is baseline weekday sun exposure, not a post-intervention measure.

The registry classifies the phase as NA. The study dates and further protocol details do not establish the rationale for the design choices. The trial's original sample-size justification, allocation ratio, masking rationale, and planned statistical analysis are not reported in the registry record. Nor are sponsor-reported inferential analyses available in the record. The comparisons discussed in the statistical interpretation are simple, unadjusted recalculations from posted group summaries, rather than a substitute for a prespecified trial analysis.

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.

Only the first 6 of 8 groups are shown.

Overall Study

Reasons for not completing this period:

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: Participants with at least one child ages 10 years of age or younger completed additional questions about the child's primary prevention activities

Only the first 6 of 9 groups are shown.

6. Primary Endpoint

The registry lists the primary outcome as Weekday Sun Exposure - NHW - Baseline, measured over Baseline.

The primary endpoint is the self-reported average number of hours spent outside during weekdays by the Non-Hispanic White Population at baseline. The registry gives the unit as hours and describes the result as a least-squares mean with a standard error. This is a continuous measure: it records a quantity on a numerical scale rather than a count of events or a yes-or-no response.

Weekday time outdoors is a behavioral exposure measure relevant to the study's focus on melanoma-risk behavior. It is not a measure of melanoma, another skin cancer, or a clinical diagnosis. It also does not directly measure sun protection, such as whether participants used a particular protective behavior. The outcome is self-reported, so it reflects participants' reports of time outside rather than an objective measurement.

The timing is important for interpretation. The registry specifies baseline, before the intervention information, as the primary timeframe. Baseline values can describe the groups' starting exposure, but they cannot by themselves show an intervention-related change. The registry's specific rationale for choosing baseline weekday exposure as the primary endpoint is not reported in the registry record.

7. Results Posted in the Registry

• MC1R Average Risk - Intervention- Non-Hispanic White Population: mean 1.30 versus 1.27 on control; difference 0.03 (95% CI -0.05 to 0.11), standardized effect d = 0.07; z-test p = 0.480.
• MC1R Higher Risk- Control - Non-Hispanic White Population: mean 1.26 versus 1.27 on control; difference -0.01 (95% CI -0.09 to 0.07), standardized effect d = -0.02; z-test p = 0.814.
• MC1R Higher Risk - Intervention- Non-Hispanic White Population: mean 1.29 versus 1.27 on control; difference 0.02 (95% CI -0.06 to 0.10), standardized effect d = 0.04; z-test p = 0.637.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Weekday Sun Exposure - NHW Children - Baseline

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard errors.
• Result:
  • MC1R Average Risk - Intervention- Non-Hispanic White Population: mean 1.50 versus 1.31 on control; difference 0.19 (95% CI -0.07 to 0.45), standardized effect d = 0.42; z-test p = 0.158.
  • MC1R Higher Risk- Control - Non-Hispanic White Population: mean 1.42 versus 1.31 on control; difference 0.11 (95% CI -0.13 to 0.35), standardized effect d = 0.21; z-test p = 0.361.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between MC1R Average Risk - Intervention- Non-Hispanic White Population and the control. The interval gives the range of effects that remain compatible with the data.
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between MC1R Higher Risk- Control - Non-Hispanic White Population and the control. The interval gives the range of effects that remain compatible with the data.

Weekday Sun Exposure - NHW Children - After Intervention

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard errors.
• Result:
  • MC1R Average Risk - Intervention- Non-Hispanic White Population: mean 1.23 versus 1.29 on control; difference -0.06 (95% CI -0.40 to 0.28), standardized effect d = -0.11; z-test p = 0.727.
  • MC1R Higher Risk- Control - Non-Hispanic White Population: mean 1.34 versus 1.29 on control; difference 0.05 (95% CI -0.23 to 0.33), standardized effect d = 0.08; z-test p = 0.724.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between MC1R Average Risk - Intervention- Non-Hispanic White Population and the control. The interval gives the range of effects that remain compatible with the data.
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between MC1R Higher Risk- Control - Non-Hispanic White Population and the control. The interval gives the range of effects that remain compatible with the data.

Weekend Sun Exposure - NHW Children - Baseline

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard errors.
• Result:
  • MC1R Average Risk - Intervention- Non-Hispanic White Population: mean 2.29 versus 2.23 on control; difference 0.06 (95% CI -0.16 to 0.28), standardized effect d = 0.16; z-test p = 0.599.
  • MC1R Higher Risk- Control - Non-Hispanic White Population: mean 2.33 versus 2.23 on control; difference 0.10 (95% CI -0.11 to 0.31), standardized effect d = 0.20; z-test p = 0.347.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between MC1R Average Risk - Intervention- Non-Hispanic White Population and the control. The interval gives the range of effects that remain compatible with the data.
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between MC1R Higher Risk- Control - Non-Hispanic White Population and the control. The interval gives the range of effects that remain compatible with the data.

The numerical secondary summaries available for the Non-Hispanic White children's measures cover weekday exposure at baseline, weekday exposure at 12 months, and weekend exposure at baseline. Across these measures, the recalculated group contrasts vary in direction and magnitude. Their intervals include zero, so the available summaries do not give a consistent, precise separation between the compared groups. Some listed secondary outcomes concern sunburns and intentional tanning, but numerical results for those measures are not reported in the registry record.

This broad pattern does not change the interpretation of the primary result. The primary endpoint is weekday sun exposure among the Non-Hispanic White Population at baseline, while the secondary measures include children's reports and a later timeframe. Those are related behavioral topics but are not interchangeable outcomes or populations. A secondary measure at 12 months is temporally more relevant to change after information than the baseline primary endpoint, but the registry record does not report sponsor inferential analyses for that measure. The available descriptive values alone do not establish an intervention effect.

Secondary findings generally carry less weight than a prespecified primary analysis, especially when many outcomes and comparisons are examined. The registry lists 86 outcome measures, and the analysis listing contains no reported analyses. A multiplicity strategy and the prespecified hierarchy among outcomes are not reported in the registry record. Without that context, isolated unadjusted patterns may arise by chance and should be treated as exploratory rather than definitive.

The reported outcomes span different behaviors, timeframes, and participant groups, which can also make a single overall interpretation misleading. The numerical summaries can help indicate what was measured and how estimates vary, but they do not support pooling unlike measures into one conclusion. The unreported secondary results and absence of formal analysis details further constrain any broad claim about behavioral response.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Weekday Sun Exposure - NHW Children - Baseline
• Weekday Sun Exposure - NHW Children - After Intervention
• Weekend Sun Exposure - NHW Children - Baseline
• Weekend Sun Exposure - NHW Children - After Intervention
• Sunburns - NHW Children - Baseline
• Sunburns - NHW Children - After Intervention
• Outdoor International Tanning - NHW Children - Baseline
• Outdoor Intentional Tanning - NHW Children - After Intervention

9. Statistical Interpretation

10. Statistical Methods Explained

What does a least-squares mean represent?

A least-squares mean is a mean reported from a statistical model, rather than necessarily a raw arithmetic average. The registry identifies the primary parameter as a least-squares mean and reports a standard error for each group. The model used to obtain those means, including any covariates or adjustment factors, is not reported in the registry record. The posted means can be read as the estimated average weekday outdoor hours for each listed group, but the missing model details limit interpretation of how they were adjusted.

What does the standard error describe?

A standard error describes the uncertainty in an estimated mean due to sampling variation under the analysis that produced it. It is not the spread of individual participants' outdoor hours. A larger standard error means an estimate is less precise, while a smaller one indicates greater precision under the same general framework. The primary group summaries report standard errors of 0.03. The registry does not report participant-level distributions, so the standard errors do not show how variable individual reports were.

How should the mean differences be understood?

A mean difference expresses the estimated distance between two group means in the outcome's original unit, here hours. A value above zero indicates the first named group has a higher estimated mean than the comparator as ordered in the reported contrast; a value below zero indicates a lower mean. The primary contrasts were recalculated simply from the posted summary statistics. They are unadjusted comparisons and should not be confused with a sponsor's fitted model or prespecified test.

These recalculations also use an approximate pooled standard deviation derived from the reported standard errors and group sizes. Such a conversion is a practical way to describe standardized differences when only summary results are available. It does not recover the original participant-level variation exactly, and the record does not provide enough analysis detail to verify the model underlying the least-squares means. The results are therefore descriptive recalculations, not replacements for an original trial analysis. No discrepancy between the posted result and the recalculation is flagged in the record.

What does a confidence interval add?

A confidence interval presents a range of values compatible with the estimate under the calculation's assumptions. For the primary comparisons, the intervals include zero, the value corresponding to no mean difference. This indicates that the estimates are not precise enough to rule out no difference using these intervals. It does not assign a probability to a particular true value, and it does not show that the groups are equivalent. A formal equivalence conclusion would require an equivalence margin and an analysis designed for that purpose; neither is reported in the registry record.

What does an unadjusted p-value say?

An unadjusted p-value measures how unusual a result at least as extreme as the observed result would be under a specified null model, subject to the analysis assumptions. It is not the probability that the null hypothesis is true, nor does it measure the size or practical importance of a difference. The posted primary recalculations have unadjusted p-values of 0.48, 0.814, and 0.637. They should be read alongside the estimated differences and intervals, rather than as stand-alone verdicts.

The record reports 86 outcome measures and no reported analyses in the analysis listing. The statistical plan, including any multiplicity strategy, model specification, analysis population, missing-data method, and interim analyses, is not reported in the registry record. Consequently, the recalculated p-values do not account for any multiplicity procedure and cannot be treated as the trial's definitive inferential results. These limitations matter particularly when many outcomes or comparisons are considered.

11. Confidence Intervals and Precision

The primary group means are reported with standard errors of 0.03. That common reported standard error conveys the estimated precision of each group mean, but it does not describe the spread of individual outdoor-time reports. The registry does not provide primary confidence intervals for the individual group means.

For each of the three unadjusted primary contrasts, the recalculated confidence interval includes zero. In practical terms, the data summaries are consistent with a range of possible mean differences that includes no difference as well as values in either direction. The point estimates are close to zero, but the interval—not the point estimate alone—shows the uncertainty that remains. The intervals do not establish equivalence, because no equivalence margin or equivalence analysis is reported in the registry record.

Precision also depends on how the results were produced. The contrasts are approximate, unadjusted recalculations using posted least-squares means and standard errors. The original model details are not reported in the registry record, and the approximate standard deviations used for planning calculations are derived from those summaries. No participant-level data or sponsor-reported inferential analysis is available in the record to refine or validate these uncertainty estimates.

Finally, precision around a baseline contrast is not the same as precision around an intervention effect. Because the primary measure is recorded at baseline, its intervals cannot quantify the effect of receiving personalized rather than standard information. Post-intervention estimates and a suitable analysis would be needed to address that question. The absence of such a primary analysis in the registry record limits what can be concluded, regardless of the apparent closeness of the baseline means.

12. 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 planning figures are participants per arm, not total events. They are illustrations based on the observed effect, not the trial's original design calculation. The listed assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set in turn to 100%, 75%, or 50% of the observed effect. The trial's own original sample-size assumptions and justification are not reported in the registry record.

The 80% power column gives the estimated participants per arm for a hypothetical study to have an 80% chance of detecting the specified effect if that effect were the true one and the planning assumptions held. The 90% power column gives the corresponding estimate for a higher chance of detection under those same assumptions. These are planning quantities, not guarantees about a future study.

For a given comparison, the planning figures rise as the target effect becomes smaller: a smaller difference is harder to distinguish from random variation, so more participants are needed under the stated assumptions. The figures can be very large when the observed difference is close to zero. They should be read as conditional illustrations tied to the observed estimate, rather than as evidence that a study had adequate or inadequate power for its original objective.

This is not observed power. It does not measure whether the completed trial succeeded at its objectives, and it cannot replace interpretation of estimates and confidence intervals. The calculation is unadjusted and assumes equal allocation between the two arms; it does not represent possible adjustments, clustering, loss to follow-up, or other design features unless those are built into the assumptions listed in the registry record.

13. 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 = 0.030; pooled standard deviation σ = 0.451.
2. n = 2 × (1.96 + 0.842)² × 0.451² / 0.030² = 3,555.6, rounded up to 3,556 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 <- 0.03                      # observed difference in means
sigma <- 0.451498613267754                     # 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(3509467)
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 = 3,556 (80% power), 4,760 (90% power)
 75% of observed effect: n per arm = 6,321 (80% power), 8,463 (90% power)
 50% of observed effect: n per arm = 14,223 (80% power), 19,040 (90% power)
power.t.test: 3556.5 
Simulated power at n = 3,556 per arm: 0.802 (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.

14. Multiplicity, Missing Data and Analysis Populations

The registry lists 86 outcome measures, creating the possibility of many comparisons across behaviors, populations, and timepoints. The record does not report a multiplicity adjustment, a hierarchy for interpreting endpoints, or a prespecified distinction between confirmatory and exploratory analyses. The unadjusted p-values from simple recalculations therefore should not be treated as though they account for testing multiple outcomes. When many results are examined, some apparently notable findings can occur by chance even when no underlying effect exists.

Missing-data procedures are not reported in the registry record. The posted summaries do not explain how participants with missing responses were handled, whether the same participants contributed at different timepoints, or whether any imputation or sensitivity analysis was used. The available group counts indicate that the analyzed groups vary by outcome, but the reasons for those differences are not reported. This makes it difficult to judge whether the summaries represent the same participant sets or whether missingness could affect comparisons.

The registry record also does not report the analysis population definition, such as whether results follow assignment regardless of intervention receipt, or whether another population was used. It does not specify the original statistical model, covariate adjustment, handling of repeated measurements, interim analyses, or the planned approach to hypothesis testing. Those details are important for interpreting randomized studies and for distinguishing baseline description from an intervention-effect analysis.

Because no sponsor-reported analyses are listed, the numerical contrasts discussed are simple unadjusted recalculations from posted summaries. They cannot resolve the missing analysis-plan information or establish that the calculations match the original protocol. The record's silence on these matters should not be filled with assumptions about what investigators planned or performed.

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

The posted primary data describe baseline self-reported weekday time outdoors in the Non-Hispanic White groups. The group means are close, and all three recalculated primary contrasts have confidence intervals that include zero. These observations support a cautious descriptive statement: the available baseline summaries do not show a clear separation in weekday outdoor hours among the compared groups.

They do not show whether personalized risk information changed behavior. The primary endpoint is measured at baseline, before the information intervention. A baseline difference is not an intervention effect, and a baseline similarity cannot demonstrate that the intervention had no effect later. The registry record would need to report appropriate post-intervention results and an analysis comparing the randomized groups over the relevant timeframe to address behavior change.

The endpoint is also a self-reported behavioral measure, not a clinical outcome. It does not establish whether participants developed melanoma or another skin cancer, and it does not directly establish whether they used protective measures. Nor does it establish a change in a child's behavior, since the primary result concerns the Non-Hispanic White Population and not the children's secondary measures.

Uncertainty matters. Intervals that include zero leave open both no difference and differences in either direction within the range of the interval. A non-significant unadjusted p-value is not proof of equivalence, and the registry record reports no equivalence margin. In addition, the comparisons are recalculated rather than sponsor-reported model results; the original analysis details are not reported.

Accordingly, the posted primary result is best understood as a baseline description with uncertainty. It does not establish benefit, lack of benefit, or clinical impact for the personalized information. Conclusions about intervention-related behavior change, outcomes in the Hispanic groups, and the unreported secondary measures are not reported in the registry record.

16. Why This Trial Matters Statistically

This study raises a useful statistical distinction between an outcome's subject matter and its timing. Weekday outdoor exposure is relevant to the study's behavioral focus, but a baseline measurement precedes the information intervention. The resulting primary summaries characterize starting behavior; they do not, on their own, estimate change attributable to randomized information. Recognizing that distinction prevents a baseline comparison from being mistaken for a treatment-effect analysis.

The record also illustrates why effect estimates and uncertainty should be read together. The reported means are close and the recalculated intervals include zero, but that combination is not proof that groups are identical. It indicates that the available summaries do not pin down a difference with sufficient precision to exclude no difference. A properly framed conclusion separates absence of a clear signal from evidence of equivalence.

Another statistical issue is the breadth of measurement. The registry lists many outcomes spanning different behaviors, groups, and timepoints. Without a reported multiplicity plan or hierarchy, secondary results are difficult to rank as confirmatory evidence. The number of measured outcomes makes transparent analysis planning particularly important, while the absence of sponsor-reported analyses limits confidence in any post hoc synthesis.

Finally, the sample-size illustrations show how planning depends on the size of the effect one seeks to detect. Smaller target effects require more participants under the stated assumptions. Those calculations are not evidence about observed power or the original design rationale. Together, these considerations demonstrate the value of clear endpoint timing, prespecified analyses, and complete reporting when evaluating behavioral interventions.

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 principal limitation for interpreting the primary result is that the endpoint is explicitly a baseline measure. It cannot quantify change after personalized or standard information. The record includes a 12-month secondary measure for weekday exposure among children, but the numerical summaries and absence of reported inferential analyses do not supply a primary intervention-effect estimate.

The primary outcome is self-reported average weekday hours outdoors. The record does not report an objective exposure measure, validation information, or details of how the question was administered. The endpoint also measures time outside rather than sun protection behavior or skin-cancer incidence, so it represents only one aspect of the study's behavioral focus.

Numerical primary results available in the record concern the Non-Hispanic White groups. Although the study includes Hispanic groups, their numerical primary summaries are not reported in the registry record. The displayed secondary information is also incomplete relative to the listed outcome topics: numerical results for some outcomes, including sunburns and intentional tanning, are not reported in the registry record.

There are no sponsor-reported inferential analyses in the analysis listing. The original model, adjustment strategy, missing-data methods, analysis population, multiplicity plan, and sample-size justification are not reported in the registry record. The unadjusted comparisons are approximate recalculations from summary statistics, so they should not be interpreted as the trial's definitive adjusted analysis. These limitations constrain both the strength and the scope of conclusions drawn from the posted data.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Using MC1R Genotype to Impact Melanoma Risk Behavior — NCT03509467.
• Registry record last updated 2025-12-19; status last verified 2025-12.
• Results first posted 2023-11-21.
• 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 randomized, parallel-group behavioral study with no masking and enrollment of 2054 participants. It evaluated personalized versus standard melanoma-risk information after MC1R genotype determination. The primary outcome is baseline self-reported weekday outdoor hours in the Non-Hispanic White Population, reported as least-squares means with standard errors.

The posted primary group means range from 1.26 to 1.30 hours, with standard errors of 0.03. Simple unadjusted recalculations produce three contrasts whose confidence intervals include zero. Because the primary measure is baseline, these results describe starting exposure and do not estimate the effect of the information intervention.

The registry lists 86 outcome measures, but no sponsor-reported analyses are listed. Details of the original analysis plan, multiplicity handling, missing-data approach, and sample-size justification are not reported in the registry record. Secondary summaries provide additional behavioral descriptions, but they do not resolve the lack of a reported primary post-intervention analysis.