Comparing the Pain Experience Between Patients Who Have and Who Have Not Undergone Dermatologic Procedures: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Comparing the Pain Experience Between Patients Who Have and Who Have Not Undergone Dermatologic Procedures (NCT01285947), a randomized na study. The primary outcome is Pain Rated by Subjects.

2. Clinical Question

The study description frames the question as an examination of an observation from previous clinical encounters: people without prior cosmetic-procedure experience appeared to experience more pain. The record also says that the study was designed to investigate a possible difference in pain perception. It does not report a directional hypothesis in formal statistical terms or a threshold for a difference that would be considered important.

3. Trial Design

The registry identifies this as a randomized, single-masked, parallel study and labels it a pilot study of 20 subjects. Enrollment is 20. The status is completed, with a start date of 2011-02 and primary completion in 2011-05. The sponsor is Northwestern University. The phase is listed as NA.

The results are organized into Naive Subjects and Non-Naive Subjects, with 10 participants in each group. The groups are defined by whether participants had previously undergone energy-based dermatologic procedures. The record’s randomized label does not mean that participants were randomly assigned to have or not have that prior history. The sequence, allocation method, and what was randomized are not reported in the registry record. The identity of the person or people masked is also not reported.

The parallel label indicates that the registry presents separate groups rather than a crossover comparison. However, the record does not explain the practical sequence of procedures within a visit or whether each participant received every named treatment. The interventions listed are Thermage, Needle Application, VBeam Laser, and Ulthera. Their specific roles and application details are not reported in the registry record.

The primary outcome timeframe is described as 3 hours for all treatments in one visit. Pain scores were averaged across periocular (temple), midface/cheek, and abdomen sites and across the treatments. Further information about recruitment, eligibility, treatment order, masking procedures, and the handling of missing measurements is not reported in the registry record. The stated enrollment and group counts describe the recorded study, but the record does not give a fuller account of participant flow or analysis populations.

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 Pain Rated by Subjects, measured over 3 hours for all treatments in one visit.

The primary endpoint is the mean pain rating given by participants. Pain was recorded on a visual analog scale: a 10 cm line with 0 marking no pain and 10 marking maximal pain. The participant marked the line, and the distance was measured with a ruler to obtain the score. The registry gives the unit as units on a scale and describes the summary as a mean with standard deviation.

The reported endpoint combines ratings across the periocular (temple), midface/cheek, and abdomen anatomical sites and across the different treatments. Its timeframe is 3 hours for all treatments in one visit. The registry does not report separate primary estimates for particular sites or treatments, so the posted comparison concerns the averaged score rather than a site-specific or device-specific result.

In general, a continuous pain score can retain gradations in reported experience rather than reducing responses to a simple event/no-event outcome. A mean gives a central summary, while a standard deviation describes the spread of individual scores around that mean. These summaries do not show the full score distribution or whether some participants had notably higher or lower ratings. The record does not report a threshold for a difference in scores that would be considered clinically important, nor does it report a validation or reliability assessment for the measurement in this study.

7. Results Posted in the Registry

• Non-Naive Subjects: mean 2.20 versus 2.30 on control; difference -0.10 (95% CI -1.17 to 0.97), standardized effect d = -0.08; z-test p = 0.854.

8. Statistical Interpretation

9. Statistical Methods Explained

The reported outcome is continuous, and the registry summarizes each group with a mean and standard deviation. The comparison is a mean difference: the Non-Naive Subjects mean relative to the Naive Subjects mean. The posted estimate is -0.1. In general, a mean difference keeps the original outcome’s units, so its interpretation remains in units on the pain scale rather than a relative measure. Its sign depends on the order in which groups are subtracted; the record identifies the Naive Subjects group as the comparator.

What does a mean summarize?

In general, the mean is calculated by combining observed values and dividing by their count. It represents a group’s average score, not a typical score in every sense: an average can be influenced by unusually high or low values and does not reveal the shape of the score distribution. Here, the means are 2.3 for Naive Subjects and 2.2 for Non-Naive Subjects. The standard deviations are 1.0 and 1.4. In general, a standard deviation describes how dispersed values are around the mean, but it does not specify the range of individual observations or whether values are skewed.

What is the role of the mean-difference estimate?

The estimate provides the observed contrast in average pain ratings. The registry reports -0.1, with the Non-Naive group as the comparison group and Naive Subjects as the control. This is a point estimate: it is one value drawn from data that are subject to sampling variation. A point estimate should therefore be considered alongside its confidence interval and the design that generated the observations. It is not a statement that the true difference is known exactly.

How should the p-value be understood?

The unadjusted p-value is 0.854. In general, a p-value describes how compatible the observed data are with a specified null model, under the assumptions of the test used. A larger p-value does not prove that the null model is true or that groups are equivalent. It also does not measure the probability that the observed result happened by chance. The registry reports the p-value as unadjusted; the precise test procedure, its assumptions, and any prespecified testing plan are not reported in the registry record.

Why does the confidence interval matter?

The interval for the mean difference extends from -1.166 to 0.966. In general, a confidence interval combines the estimate with information about its uncertainty. It shows a set of values reasonably compatible with the data under the interval method’s assumptions. Because this interval includes zero and values on either side, it reflects uncertainty about both the direction and magnitude of the difference. The confidence level and construction method are not reported in the registry record, so they should not be inferred from the endpoints alone.

What does the averaging imply?

The primary description says that scores are averaged over the periocular (temple), midface/cheek, and abdomen sites and over all the different treatments. In general, averaging repeated measurements can create a single participant-level summary that is easier to compare between groups, but it can conceal variation by site, treatment, or time. The record does not describe how participant-level averages were formed, how many measurements contributed to each average, or how incomplete sets of ratings were handled. It also does not report a model for within-participant correlation. Because ratings from the same person may be related, that detail could matter for an analysis that used the individual site or treatment observations rather than a single summary per participant.

What does the study design contribute?

The record labels the design randomized, single-masked, and parallel. In general, randomization can reduce systematic differences between assigned groups when the randomized element is an intervention. Here, the comparison is between groups defined by a prior-procedure history, which is not itself an assigned intervention in the posted description. The record does not specify what element was randomized, how allocation was performed, or who was masked. Those missing details limit how much can be inferred from the design labels about protection against bias in this particular comparison.

No adjustment is reported for other participant characteristics, site, or treatment. No analysis plan, model specification, or diagnostic information is reported in the registry record. The posted mean difference and unadjusted p-value should therefore be understood as the available comparison, rather than as evidence that any unreported adjustment or modeling approach was used.

10. Confidence Intervals and Precision

The mean-difference estimate is -0.1, and the reported confidence interval extends from -1.166 to 0.966. This is the main expression of precision for the group comparison: it indicates that the point estimate is uncertain, with compatible values extending from a negative difference to a positive one. The point estimate alone would not convey that range. Conversely, the interval should not be read as a list of observed differences among individual participants; it describes uncertainty around the estimated group contrast.

In general, a confidence interval is constructed using a statistical method and assumptions about the data. Across repeated studies conducted under suitable conditions, intervals made by a method with a stated confidence level would capture the target parameter at the corresponding long-run frequency. That general interpretation does not mean that there is a corresponding probability that the fixed parameter lies in this particular interval. The confidence level and interval method are not reported in the registry record, so the interval endpoints can be quoted, but the level should not be presumed.

The interval includes zero, as well as values on both sides of zero. This means the posted estimate does not precisely establish the direction of the mean difference. The interval also spans values that are farther from zero than the point estimate. The registry does not state what difference on this scale would be clinically important, so statistical uncertainty cannot be translated into a judgment about practical importance.

The group standard deviations, 1.0 for Naive Subjects and 1.4 for Non-Naive Subjects, indicate variation in scores within each group, but they do not substitute for the uncertainty interval around the mean difference. The result also reflects averaging across treatment types and anatomical sites. Precision for separate treatments, sites, or subgroups is not reported in the registry record.

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. They are illustrations based on the observed effect rather than the original trial’s design. The listed assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each planning scenario uses the stated fraction of the observed effect as the effect to detect. The original sample-size assumptions for the trial are not reported in the registry record.

The 80% power column gives the modeled number of participants per arm for a future study to have an 80% chance of detecting the selected effect under those assumptions, if that effect and the assumptions were correct. The 90% power column gives the corresponding planning number for a 90% chance. These are planning targets, not findings from this pilot study. They are not observed power.

The rows describe planning for 100% of the observed effect, 75% of the observed effect, and 50% of the observed effect. As the effect to be detected becomes smaller, the calculated participant requirement increases. This follows the general principle that smaller differences are harder to distinguish from sampling variation and therefore require more information, all else being equal.

The planning figures are very large because the observed mean difference is small relative to the variability and the assumptions use that observed effect as the basis for planning. Such calculations can be unstable when a pilot estimate is imprecise, and the actual effect in a future study may differ. The registry does not report a trial-specific design justification, so the planning values should not be mistaken for the study’s intended enrollment or a definitive recommendation for a future study.

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 = -0.100; pooled standard deviation σ = 1.217.
2. n = 2 × (1.96 + 0.842)² × 1.217² / -0.100² = 2,323.3, rounded up to 2,324 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 <- -0.0999999999999996                      # observed difference in means
sigma <- 1.21655250605964                     # 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(1285947)
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 = 2,324 (80% power), 3,111 (90% power)
 75% of observed effect: n per arm = 4,131 (80% power), 5,530 (90% power)
 50% of observed effect: n per arm = 9,294 (80% power), 12,441 (90% power)
power.t.test: 2324.2 
Simulated power at n = 2,324 per arm: 0.796 (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 describes one primary outcome: mean pain rated by subjects. It reports no secondary outcome measures. The primary comparison averages across anatomical sites and across treatments, while the named sites and interventions could also invite separate comparisons. The record does not report separate tests for those components, and no multiplicity adjustment is described.

In general, multiplicity arises when several outcomes, groups, time points, or subgroup comparisons are tested. Conducting many tests can increase the chance of obtaining at least one apparently unusual result even when no underlying effect exists. Statistical plans may address this by defining a primary comparison in advance, controlling an overall error rate, or treating exploratory comparisons as hypothesis-generating. Which approach was used in this study is not reported in the registry record. The unadjusted p-value should not be interpreted as accounting for any unreported additional tests.

The registry reports a primary mean and standard deviation for each group and an unadjusted mean-difference comparison. It does not provide an analysis plan, prespecified hypothesis, model specification, or description of any interim analysis. Whether there were interim analyses is not reported in the registry record. The record does not state whether results were adjusted for participant characteristics, treatment, anatomical site, or repeated measurements.

Missing-data handling and the analysis population are also not reported in the registry record. The posted group counts are 10 for Naive Subjects and 10 for Non-Naive Subjects, but the record does not explain whether these represent all enrolled participants, all participants with usable primary outcome data, or a specified analysis set. It does not describe withdrawals, incomplete ratings, exclusions, or imputation. These details matter because an average based on incomplete outcome measurements may represent a different set of observations from the one implied by enrollment.

The registry’s randomized label does not resolve these questions. The history groups are described by prior exposure, and the record does not specify what was randomized or how the randomization related to the posted group comparison. Without analysis and missing-data details, the result is best read as the reported summary and comparison rather than as a fully specified confirmatory analysis.

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 1% reporting threshold.

The registry reports zero serious adverse events among the 10 participants at risk in Naive Subjects and zero among the 10 participants at risk in Non-Naive Subjects. For other adverse events, it likewise reports zero among the 10 participants at risk in each group. These are the recorded event counts; they do not establish that no event could occur in a larger group or under different observation conditions.

The deaths fields are null, so deaths are not reported in the registry record as a count. A null value should not be recast as zero. The record does not provide definitions of serious or other adverse events, the method or duration of safety surveillance, event-relatedness assessments, or a detailed listing of events. The primary outcome timeframe is described as 3 hours for all treatments in one visit, but the record does not explicitly specify that this is the safety follow-up period.

These safety figures are descriptive and limited to the groups and reporting available in the registry. With no events recorded in the posted counts, the record does not quantify the range of possible event rates or establish comparative safety.

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

The posted result describes average pain ratings in the study’s two prior-exposure groups. Naive Subjects had a mean of 2.3, and Non-Naive Subjects had a mean of 2.2. The estimated mean difference, Non-Naive relative to Naive, is -0.1. The reported interval from -1.166 to 0.966 includes zero and values in both directions, while the unadjusted p-value is 0.854. Taken together, these statistics show a small estimated difference with substantial uncertainty about its direction and size.

This result does not prove that the groups have identical pain experiences. It also does not establish that prior experience lowers or raises pain, because prior exposure defines the groups and was not described as a randomized assignment. The study design labels do not show that exposure history itself was randomized. Differences between the groups may reflect factors not described or adjusted for in the registry.

The outcome is an average across anatomical sites and treatments. The posted comparison does not establish what the ratings were for an individual device, site, participant, or treatment application. Nor does it define what score difference would matter to participants or clinicians. The registry’s description and statistics are not a basis for medical advice or an individual prediction.

The study is labeled a pilot study, and the posted group sizes are 10 participants each. The findings can be read as a record of the observed comparison and its uncertainty in this study. They do not by themselves establish whether the same estimate would recur in another sample, how it might vary across populations, or what might be found with a different measurement or analysis. Information about the trial’s original sample-size rationale, analysis plan, missing data, and masking implementation is not reported in the registry record.

16. Why This Trial Matters Statistically

This trial raises a useful statistical distinction between a randomized trial label and the specific comparison being interpreted. The groups are defined by prior procedure history, while the record also identifies the study as randomized. Because the registry does not say what was randomized, the label alone cannot support treating prior exposure as a randomized intervention. Clear reporting of the randomized element is essential when readers assess whether an observed group difference can be interpreted causally.

The endpoint also illustrates how an overall average can answer a focused question while masking detail. The primary score averages across multiple anatomical sites and different treatments. That summary is compact, but it cannot show whether pain ratings varied meaningfully by site or procedure. Separate estimates, if planned and reported, would answer different questions and would need to be interpreted with attention to multiplicity and precision.

The confidence interval makes the uncertainty visible in a way the point estimate and p-value cannot do alone. The mean difference is close to zero, but the interval extends to values on either side. For a pilot study, that distinction matters: a small point estimate is not the same as precise evidence for no difference. The registry does not state a clinically important threshold, leaving practical interpretation open.

Finally, planning calculations based on an observed pilot effect are illustrative rather than a direct report of the original design. When a small observed difference is used as the target, planning requirements can become large, and uncertainty in the pilot estimate carries forward. The record’s sparse details about allocation, masking, analysis populations, and missing ratings also demonstrate why outcome estimates need to be read alongside methods and reporting context.

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 leaves important design details unspecified. Although the study is labeled randomized and single-masked, it does not identify what was randomized, the allocation method, or who was masked. Since the principal comparison is between groups defined by prior procedure history, readers cannot assume that this history was randomized. The record also does not explain treatment order or whether all participants received all listed procedures.

The outcome is an average across the periocular (temple), midface/cheek, and abdomen sites and across treatments. This combined summary does not report site-specific or treatment-specific pain ratings. The registry does not explain how the averages were calculated or whether every participant contributed a complete set of ratings. Missing-data procedures, participant flow, exclusions, and the analysis population are not reported.

The registry does not report the confidence level or method used to construct the interval, the statistical test behind the unadjusted p-value, a prespecified analysis plan, or a clinically important difference. It also does not report adjustment for possible differences between exposure-history groups, nor details about repeated-measure handling. These gaps limit assessment of the assumptions and interpretability of the comparison.

Safety reporting is limited to event counts and at-risk group counts. Definitions, surveillance duration, attribution, and details for individual events are not reported; deaths are not reported in the registry record. Generalizability is also difficult to assess because eligibility criteria, recruitment details, and further participant characteristics are not reported. These limitations do not change the posted numbers, but they constrain what can be inferred from them.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Comparing the Pain Experience Between Patients Who Have and Who Have Not Undergone Dermatologic Procedures — NCT01285947.
• Registry record last updated 2021-12-06; status last verified 2021-12.
• Results first posted 2014-02-05.
• 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.

21. Record Summary

NCT01285947 is a completed pilot study sponsored by Northwestern University. The registry describes a randomized, single-masked, parallel design and enrollment of 20. The groups are Naive Subjects and Non-Naive Subjects, with 10 participants in each, defined by prior experience with energy-based dermatologic procedures.

The primary outcome is mean subject-rated pain on a visual analog scale from 0, no pain, to 10, maximal pain, averaged across the listed sites and treatments during 3 hours for all treatments in one visit. The reported means are 2.3 and 2.2, with a mean difference of -0.1, a confidence interval from -1.166 to 0.966, and an unadjusted p-value of 0.854. No secondary outcome measures are reported. Further design and analysis details, including what was randomized and who was masked, are not reported in the registry record.