This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Ethnic Differences in Response to Topical Capsaicin: A Psychophysical Study on Healthy Subjects (NCT00655811), a randomized phase 4 study. The primary outcome is Ethnic Differences in Burning Pain Induced by Topical Capsaicin.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00655811 |
| Phase | Phase 4 |
| Condition | Healthy |
| Allocation | Randomized |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 40 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Wake Forest University |
| Results posted | Yes |
2. Clinical Question
Population
Healthy subjects; the registry record does not name the ethnic groups or describe other eligibility details.
Intervention
Capsaicin 0.1% cream applied to the volar side of the forearm.
Comparator
Placebo moisturizing cream with no active ingredient applied to the opposite forearm.
Primary question
How does burning pain after topical capsaicin, rated on a continuous visual analog scale, differ across ethnic groups?
The study asks whether people described as belonging to different racial or ethnic groups respond differently to topical capsaicin, with burning-pain intensity as the primary outcome. Its stated purpose also concerns pain levels following application. The registry record does not identify the groups being compared, explain how ethnicity was classified, or report the group-specific pain ratings.
The intervention description pairs capsaicin cream on one forearm with placebo moisturizing cream on the opposite forearm. This suggests that each participant may have received both applications, but the record classifies the model as single-group and does not fully explain the analysis structure or allocation procedure. It also labels allocation randomized without describing what was randomized. Those record details should not be reconciled by assuming a specific protocol.
The primary question is not simply whether capsaicin produces a rating: it concerns variation in the rating across ethnic groups. A direct answer would require reported outcome results by group and a stated comparison or analysis. Those results and the associated comparison are not reported in the registry record. The registry does list secondary outcomes concerning thermal sensory thresholds and burning or pain ratings between capsaicin and placebo, but it does not report their results in the record.
3. Trial Design
The record describes a Phase 4 study that is completed, with 40 participants enrolled. It lists healthy subjects as the condition of interest and identifies Wake Forest University as the sponsor. The recorded study start is 2008-02, and primary completion is recorded as 2008-08. These entries describe the registry record; they do not provide information about recruitment progress or the conduct of individual study visits.
Allocation is classified as randomized, masking as none, and the model as single-group. The intervention descriptions specify capsaicin 0.1% cream on the volar side of one forearm and placebo moisturizing cream on the opposite forearm. The placebo is described as having no active ingredient. The record does not explain the randomization sequence, whether application side or order was randomized, or how the randomized allocation classification relates to the single-group model and paired forearm descriptions. It is therefore not possible to reconstruct the exact assignment procedure from the registry record.
The primary endpoint is a continuous rating of burning pain after capsaicin application. Ratings were collected on a 100-mm continuous visual analog scale, described as ranging from no sensation to the strongest imaginable pain sensation. Participants were also asked whether they experienced any nonpainful sensation. The primary timeframe is 1 day. The registry lists 3 outcome measures and 8 analyses, but does not detail the analysis populations, statistical models, or which analyses correspond to each outcome.
The record does not report a sample-size justification, enrollment targets by ethnic group, or planned methods for handling repeated measurements or within-participant comparisons. It also does not provide a full protocol narrative. The listed study design classifications and intervention descriptions are informative, but they do not fill those gaps.
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
| Stage | Capsaicin and Placebo |
|---|---|
| STARTED | 40 |
| COMPLETED | 40 |
| NOT COMPLETED | 0 |
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.
| Characteristic | Unit | Capsaicin and Placebo |
|---|---|---|
| Participants analysed | 40 | |
| Age, Categorical: <=18 years | Participants | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 40 |
| Age, Categorical: >=65 years | Participants | 0 |
| Sex: Female, Male: Female | Participants | 20 |
| Sex: Female, Male: Male | Participants | 20 |
| Race/Ethnicity, Customized: African Americans | Participants | 10 |
| Race/Ethnicity, Customized: Caucasians | Participants | 10 |
| Race/Ethnicity, Customized: East Asians | Participants | 10 |
| Race/Ethnicity, Customized: Hispanic | Participants | 10 |
| Region of Enrollment: United States | Participants | 40 |
6. Primary Endpoint
The registry lists the primary outcome as Ethnic Differences in Burning Pain Induced by Topical Capsaicin, measured over 1 day.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Standard Error |
| Unit | units on a scale |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is the intensity of burning pain after topical capsaicin application, measured using a continuous visual analog scale. The scale is described as 100-mm long, with 0 representing no sensation and 100 representing the maximum, strongest imaginable pain sensation. The recorded timeframe is 1 day. Participants were also asked whether they experienced any nonpainful sensation, but the record does not clarify whether that response contributes to the primary endpoint.
A continuous rating can retain gradations in reported sensation rather than reducing responses to a simple yes-or-no pain category. That can be useful when the research question concerns differences in intensity. The registry identifies the primary measure as a mean and its dispersion as a standard error. In general, a mean describes the average rating in a group, while a standard error describes uncertainty around an estimated mean; it is not a measure of how widely individual ratings vary. These are general statistical definitions, not a description of reported trial estimates.
The endpoint fits the stated interest in burning pain induced by topical capsaicin and possible ethnic differences in response. However, the registry record does not report the observed ratings, mean values, standard errors, ethnic-group categories, or a between-group estimate. It therefore does not permit assessment of the size or precision of any observed difference.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry describes a study intended to assess ethnic differences in burning pain after topical capsaicin. Its primary outcome is a continuous rating, collected after application and reported on a 100-mm scale. The record identifies the endpoint and the general study question, but it does not include the primary outcome values or a result comparing ethnic groups. Consequently, no direction, magnitude, or precision of an ethnic-group difference can be stated from this record.
The record also does not identify the ethnic groups. Without those categories, readers cannot determine which populations were included or how broadly any eventual findings might apply. The record does not describe how group membership was established or whether enrollment was balanced across groups. These omissions matter because the primary question depends on comparing ratings across groups, not merely describing an overall rating after capsaicin.
The design classifications need cautious reading. The record labels allocation randomized, masking none, and the model single-group, while its intervention descriptions place capsaicin and placebo on opposite forearms. This may describe a within-participant arrangement, but the record does not explicitly state that all participants received both applications or explain how assignment was randomized. The precise design and the intended comparison cannot be reconstructed with confidence from those entries alone.
The registry lists secondary outcomes on thermal sensory thresholds and differences in burning or pain ratings between capsaicin and placebo. It reports 3 outcome measures and 8 analyses, but does not provide their results or define the analyses. These entries establish that additional outcomes and analyses were registered; they do not show what those analyses found.
The adverse-event record lists 40 at risk in each of the capsaicin and placebo groups, with zero serious events and zero other adverse events recorded in each. These entries are descriptive counts, not estimates that establish the absence of risk. The death entries are not reported. The registry record does not describe monitoring or the way adverse events were collected.
Any planning illustration based on an observed effect should be distinguished from an observed trial result. The record describes such illustrations as using two-sided significance level 0.05, equal allocation, a normal approximation, and effects defined as fractions of the observed effect. The numerical planning values are not reported in the registry record. Such calculations are planning aids, not observed power, and cannot substitute for the missing primary estimate or its uncertainty.
9. Statistical Methods Explained
The registry identifies the primary outcome as a mean of a continuous measure and specifies standard error as the dispersion statistic. These terms describe different aspects of the data. In general, a mean is the average of participant ratings in a group. A standard error describes the statistical uncertainty in an estimated mean; it is not the same as the spread of individual participant ratings. A standard deviation, by contrast, describes variation among individual observations. No numerical mean or standard error for the primary outcome is reported in the registry record.
The primary measure is a continuous visual analog rating of burning pain. The record describes a 100-mm scale, with endpoints of no sensation and the strongest imaginable pain sensation. A continuous scale can represent gradations in intensity. This can preserve more detail than classifying a response only as pain present or absent. The record additionally says that participants were asked whether they experienced any nonpainful sensation, but it does not give the response options or explain how those responses were incorporated into analysis.
In general, estimates of a group mean are more informative when accompanied by an uncertainty interval. A confidence interval gives a range of values compatible with the data and the statistical model at a stated confidence level. Its width reflects both the observed information and the assumptions used to estimate uncertainty. The registry record does not report a confidence interval for the primary outcome, a between-group estimate, or the inferential method used for the primary analysis. Therefore, the precision of the primary result cannot be assessed from this record.
The research question is about ethnic differences in response, which implies a comparison across groups. A suitable interpretation would depend on the groups defined, the outcome summary in each group, and the estimate of the contrast between groups. It would also depend on whether the analysis accounted for the way treatment applications were assigned. The record describes capsaicin and placebo on opposite forearms, but does not give enough detail to establish whether measurements were analyzed as paired observations, independent groups, or another structure. It does not report the model or the handling of possible within-participant correlation.
The registry also classifies the study as randomized and unmasked. Randomization, in general, can reduce systematic differences between assigned conditions when implemented as intended. Unmasked assessment means that masking is not listed; the record does not specify who knew which cream was applied or how outcome assessment was conducted. These classifications do not, by themselves, establish how randomization was performed or whether outcome measurement could have been influenced by knowledge of the application.
The stated sample-size assumptions describe planning illustrations based on an observed effect, not the trial's original design justification. They specify a two-sided significance level of 0.05, equal allocation, and a normal approximation; the effect to detect is defined as a stated fraction of the observed effect. Such illustrations can show how a planning sample size changes under chosen assumptions. They are not observed power, do not establish that the study was adequately powered, and do not replace an estimate with uncertainty. The registry does not report its own sample-size justification or numerical planning values in the record.
In general, over-dispersion occurs when data vary more than a statistical model assumes. If a model fails to account for that extra variation, its uncertainty estimates may be too small and its intervals too narrow. This is a general consideration, not a finding about this study: the registry record does not report an over-dispersion assessment or a model to which such an assessment could be applied.
The registry lists 8 analyses across 3 outcome measures. Multiple analyses can create multiplicity: when many hypotheses are tested, the chance of at least one apparently notable result can increase if each is assessed without an appropriate strategy. General approaches include prespecifying a primary analysis, adjusting for multiple comparisons, or clearly labeling analyses as exploratory. The record does not report whether any such approach was planned or used. Nor does it identify which analysis addresses the primary question.
Missing-data methods also affect interpretation. In general, an analysis may be influenced if outcome measurements are absent for some participants, particularly when missingness is related to their unobserved ratings or group. The registry record does not report the number of participants with primary outcome measurements, the extent of missing data, or any method for addressing missing observations. The enrollment figure alone does not establish how many participants contributed to each analysis.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists 3 outcome measures and 8 analyses. It names the primary burning-pain outcome and identifies secondary outcomes concerning thermal sensory thresholds and burning or pain ratings between capsaicin and placebo. Having several outcomes or analyses is not inherently problematic, but it affects how individual findings should be interpreted. In general, repeated testing can increase the chance of finding an apparently notable result by chance if no analysis strategy accounts for the number of comparisons.
The record does not report a multiplicity adjustment, a hierarchy for testing primary and secondary outcomes, or a distinction between confirmatory and exploratory analyses. It also does not identify all 8 analyses or state which ones were prespecified. The statistical analysis plan and interim analysis procedures are not reported in the registry record. Accordingly, it is not possible to determine how multiplicity was handled or whether the reported analysis structure followed a prespecified plan.
The record does not state how many participants had usable primary outcome ratings, whether any ratings were missing, or how missing measurements were handled. It does not describe analysis populations, exclusions, or a missing-data strategy. Enrollment of 40 participants does not establish that all enrolled participants contributed data to every outcome or analysis. These details are needed to judge how complete the analyzed data were and how sensitive results might be to missing observations.
These are limitations of the registry information, not evidence that multiplicity or missing data affected the findings. Since the primary outcome results are not reported in the registry record, their influence on any estimated effect cannot be evaluated.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Capsaicin | 0 | 40 | 0.0% |
| Placebo | 0 | 40 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Capsaicin | 0 of 40 |
| Placebo | 0 of 40 |
The adverse-event entries list 40 participants at risk in the capsaicin group and 40 at risk in the placebo group. Serious adverse events are recorded as 0 in each group, and other adverse events are also recorded as 0 in each group. These are the counts listed in the registry record; they are not a guarantee that no adverse events occurred outside the recorded categories or observation process.
A zero count is most useful when interpreted alongside information about how events were defined, collected, and followed over time. The registry record does not describe event ascertainment, the duration of safety follow-up, or whether all participants were assessed in the same way. It also does not report a comparison estimate or uncertainty interval for adverse events. The number listed as at risk should not be read as proof that every participant completed safety follow-up.
The deaths field is not reported in the registry record. The adverse-event entries therefore support only a narrow description: no serious or other adverse events are recorded in either listed group, among the stated numbers at risk. They do not establish comparative safety or rule out uncommon or unrecorded events.
12. What the Result Does, and Does Not, Mean
The registry record establishes that a completed study of topical capsaicin in healthy subjects was designed to address burning-pain ratings and ethnic differences in response. It identifies capsaicin 0.1% cream, placebo moisturizing cream, the primary visual analog outcome, and a primary timeframe of 1 day. It also records 40 enrolled participants and lists several secondary outcomes.
However, the primary ratings and the comparison across ethnic groups are not reported in the registry record. The ethnic groups themselves are not named. Without those results, it is not possible to state whether ratings differed, which group had higher or lower ratings, or how large and precise any difference was. There is also no reported estimate or confidence interval with which to judge uncertainty.
The intervention descriptions place capsaicin and placebo on opposite forearms, but the record does not fully explain the allocation and analysis structure. The randomized, unmasked, single-group classifications do not resolve whether applications were randomized by side or order, or how forearm-level measurements were compared. The result interpretation would depend on these details, which are not reported in the registry record.
The listed adverse-event counts are zero for serious and other events in both groups, with 40 at risk recorded for each. Those counts are a limited safety description and should not be taken as proof that risk is absent. The record does not report death counts, safety follow-up details, or uncertainty around comparisons.
In general, a study's purpose and design can clarify the question it intended to answer, but they cannot substitute for outcome results. Likewise, planning calculations based on an observed effect are not trial findings and are not observed power. The available registry information therefore supports describing the study question and its recorded design, but not drawing a conclusion about the primary effect or the presence of ethnic differences.
13. Why This Trial Matters Statistically
This study raises a statistical question about variation in a continuous response across ethnic groups. That question requires more than an overall average: it calls for clearly identified groups, outcome summaries within those groups, and an estimate of the difference or other prespecified contrast. The registry record identifies the general question but does not report the group definitions or the comparison results, so the statistical target cannot be evaluated from the record alone.
The forearm descriptions also make the analysis structure important. If participants contribute ratings under both capsaicin and placebo, those observations may be related within a person. In general, paired observations require analysis that recognizes their dependence; treating dependent measurements as independent can misstate uncertainty. The registry describes opposite-forearm applications but does not report whether the analysis used a paired structure or another method. This is a design detail with direct implications for standard errors and interpretation.
The primary outcome uses a continuous rating, which can capture gradations in reported burning pain. Its interpretation still depends on the distribution of ratings, the quality of measurement, and the statistical summary chosen. The record specifies a mean and standard error but gives no observed values or precision estimates. The endpoint is therefore clear in concept, while its empirical result is unavailable in the registry record.
Finally, the record lists multiple outcomes and analyses but gives no multiplicity strategy or missing-data account. These omissions limit assessment of how reliably any individual finding would represent the intended primary question. The study matters statistically because it combines a group-comparison question with potentially paired treatment observations and several outcomes, yet the registry record does not supply the analytical details or outcome estimates needed to assess those issues.
14. 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 details of the target population unspecified. It identifies healthy subjects and refers to racial or ethnic groups in the study purpose, but does not name the groups, report their enrollment counts, or describe how group membership was determined. It also does not provide other eligibility criteria or explain whether enrollment represented a particular population beyond healthy subjects.
The design entries and intervention descriptions do not fully align in a way that permits reconstruction of the protocol. The record labels the model single-group and allocation randomized, and describes capsaicin and placebo on opposite forearms. It does not explain the randomization unit, application order, side assignment, or whether all participants received both creams. The analysis structure for any within-participant measurements is not reported.
The record names the primary outcome and its scale but does not report observed ratings, group-specific means, standard errors, or a comparison estimate. The results of the secondary outcomes are also not reported. The record lists 8 analyses but does not explain their methods, identify the primary analysis, or describe adjustment for multiple comparisons.
There is no reported sample-size justification for the trial or description of the intended analysis populations. The record does not state the number of participants with analyzable measurements, how missing observations were handled, or whether exclusions occurred. Safety entries lack information about event collection and follow-up; death counts are not reported.
These gaps limit interpretation of the registry information. They do not establish that the study was conducted incorrectly, nor do they indicate what results the investigators observed. They mean that the outcome findings, analytical precision, and applicability to specific ethnic groups cannot be assessed from the registry record.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Ethnic Differences in Response to Topical Capsaicin: A Psychophysical Study on Healthy Subjects — NCT00655811.
- Registry record last updated 2018-09-10; status last verified 2018-08.
- Results first posted 2017-08-14.
- 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.
Continue through the Clinical Biostats statistical pathway
Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
18. Record Summary
The completed Phase 4 study is listed as randomized, unmasked, and single-group, with 40 participants enrolled. It concerns healthy subjects and describes capsaicin 0.1% cream on one forearm and placebo moisturizing cream on the opposite forearm. The recorded start is 2008-02 and primary completion is 2008-08.
The primary endpoint is burning-pain intensity on a continuous visual analog scale, with a 1-day timeframe. The registry lists secondary outcomes involving thermal sensory thresholds and burning or pain ratings between capsaicin and placebo. It records 3 outcome measures and 8 analyses.
The primary and secondary outcome results, ethnic-group definitions, analysis methods, missing-data handling, and multiplicity strategy are not reported in the registry record. Serious and other adverse events are each recorded as 0 in both listed groups, with 40 at risk per group; deaths are not reported.