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Interpretation of SPF In vivo Results: Analysis and Statistical Explanation
By: Marc Pissavini and Olivier Doucet, Coty-Lancaster; and Olivier Brack, Statistique Industrielle KHI2 Consulting (KSIC)
Posted: March 2, 2011, from the March 2011 issue of Cosmetics & Toiletries.
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- From Cosmetics & Toiletries
- March 2011 issue, pg 172
- 8 pages
- standard deviation
- confidence interval
- standard error mean (SEM)
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Currently in Europe, sun protection products must follow many recommendations and although they are not law, compliance is expected from the cosmetic industry by regulators, consumers and the industry itself. For example, the European Commission and Colipa recommend that products provide both UVB and UVA protection, with an SPF ratio of at least one-third. SPF claims are organized into four categories: low SPFs of 6 and 10; medium SPFs of 15, 20 and 25; high SPFs of 30 and 50; and very high SPFs of 50+.1, 2
In relation, in the United States in 2007, the US Food and Drug Administration (FDA) proposed an amendment to its Final Monograph relating to sun protection.3 The proposed rules are different than Europe’s for UVA but are similar in terms of SPF. The FDA has proposed: replacing its current category descriptors of minimal and moderate respectively with the terms low, meaning SPF 2 to < 15, and medium, meaning SPF 15 to < 30; and increasing the labeled SPF value to 50 for SPF 30–50, and 50+ for SPF 50+.
Lab Practical: Statistics Translated
- The arithmetic average of SPF values indicates what the real SPF value could be.
- The standard deviation of SPF values gives an indication of a pool of heterogeneity between consumer SPF results and uncertainty on measurements.
- The CI of SPF values gives an indication of the area in which the real SPF is assumed to be.
- During sunscreen product development, the obtained SPF value is compared with the values of previous batches according to the mean SPF value and its standard deviation.
This is only an excerpt of the full article that appeared in Cosmetics & Toiletries, but you can purchase the full-text version.