TESTING


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It is beneficial for before-and-after


assessments within the same group, like pre- and post-treatment measurements on the same subjects. On the other hand, ordinary one-way ANOVA is the rigorous method to be applied when dealing with one independent variable that has more than two levels, allowing comparison of means across different groups or treatments. This method is apt for scenarios with more


than two sets of data and must be applied in studies with one treatment and more than two timepoints. Lastly, two-way ANOVA is ideal when


there are two independent variables and their interaction, examining how these variables simultaneously influence the dependent variable. This statistical tool is suitable for designs where there are multiple treatments across different groups and additional factors or variables affecting the outcome. This should be applied for placebo-controlled studies.


Confidence intervals and P-values Calculating confidence intervals around the mean differences provides a range within which the true effect of the product is likely to lie. Interpreting p-values derived from statistical


tests helps determine the significance of observed changes. A p-value less than 0.05 indicates statistically significant results. Presenting statistically significant findings along with their clinical relevance (*, **, ***, or ****) is essential. Discussing practical implications aids in


understanding the significance of observed changes. Moreover, expressing confidence or uncertainty in the conclusions drawn from statistical analyses, based on the strength of evidence and statistical rigour, adds credibility to the findings.


Population size calculation The number of volunteers included in a clinical trial is an essential aspect to be considered, since it is obvious that the results obtained for a small group of five volunteers cannot be so reliable and realistic than a big group of 100 volunteers. The number of volunteers recruited for the study has to be enough to determine statistically


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significant differences, otherwise the low potency of the statistical analysis might jeopardize the conclusions of the assessment. Based on different mechanisms to determine


the size of a population, it has been widely recognized for cosmetic clinical tests that a minimum of 20 volunteers are always necessary. Acknowledging limitations, such as small sample sizes, is crucial in interpreting statistical findings.


Control for covariates Controlling for potential confounding variables, such as age, gender, or baseline skin conditions, through techniques like multivariate analysis or regression analysis, might help to isolate the true effect of the product.


Handling missing data and outliers Addressing missing data using appropriate imputation techniques ensures the robustness of the analysis. Removing outliers or employing robust statistical methods prevents undue influence on results. Different methods, such as ROUT (Robust


regression and Outlier removal), can be used to identify outliers in the raw data, with a coefficient Q to be determined according to how aggressively the method defines the outlier (from 0.1 % to remove definitive outliers to 10 % to remove likely outliers). In order to maintain the human intravariability inherent to clinical testing, using higher levels of restriction (Q) might be interesting.


Discussion and conclusion Before and after trials serve as invaluable tools for evaluating the efficacy of cosmetic products. However, their reliability and integrity depend on the strict adherence to standardized practices and ethical considerations. Transparency, scientific rigour, and managing consumer expectations are pivotal in presenting authentic representations of product outcomes. Acknowledging limitations and potential


biases inherent in visual representations underscores the need for caution in interpreting and presenting before and after imagery. Balancing the showcase of transformative effects with the scrutiny of rigorous evaluation is pivotal


in maintaining credibility in cosmetic product evaluation. By upholding best practices and maintaining


ethical integrity, such as consistency in experimental conditions, encouraging participants to adopt similar neutral poses and facial expressions, using high-resolution and unaltered images, establishing clear timeframes and protocols for treatment application, documenting procedures, assuring participant’s compliance, using reliable instrumental innovative technologies and not only subjective evaluations, limiting the impact of external factors, avoiding ethical issues with the corresponding informed consents, employing robust statistical methods, and transparently reporting the analysis procedures and results, cosmetic product evaluations can enhance their scientific validity. Statistical analysis is prior to complement


visual representations in before and after trials, providing quantitative evidence of product efficacy and strengthening the credibility of claims made regarding cosmetic products’ effects on skin health and appearance. Altogether, the cosmetic industry can build trust, enhance accountability, and empower consumers to make informed decisions. On the other hand, establishing common


criteria to validate cosmetic efficacy claims among clinical research organizations is crucial for ensuring a level playing field within the industry. Consistent standards serve as a cornerstone for reliability and credibility, allowing for fair evaluation and comparison of products. When all parties adhere to the same rules,


it fosters transparency, builds trust among consumers, and mitigates misleading or exaggerated claims. Moreover, standardized criteria streamline the assessment process, enabling companies to invest resources more effectively in research and development, ultimately leading to the creation of safer and more effective cosmetic products. This harmonization not only benefits the


industry but also empowers consumers by providing them with accurate and consistent information to make informed choices about the products they use on their bodies.


PC January 2025 PERSONAL CARE


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