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Comparative Analysis of Shampoo Formulations on Hair Combability

This study by M.L. Garcia and J. Diaz in 1976 compared the effects of two shampoo formulations (A and B) on hair combability using 16 hair swatches and 5 replicates per swatch. Combability measurements were taken after shampooing, with shampoo as a fixed factor and swatch as random. The analysis of variance (ANOVA) showed no significant formulation differences but revealed variation in combability with different swatches.

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Comparative Analysis of Shampoo Formulations on Hair Combability

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  1. Nested Design Comparison of 2 Shampoo Formulations on Hair Combability M.L. Garcia and J. Diaz (1976). “Combability Measurements on Human Hair,” Journal of the Society of Cosmetic Chemists, Vol.27 pp.379-398

  2. Data Description • 2 Formulations of Shampoo (A and B) • 16 Hair Swatches Prepared (8 for A, 8 for B) • 5 Test Runs Made per Swatch (Replicates) • Combability Measurements made before and after shampooing (we consider only AFTER here) • Shampoo Treated as FIXED Factor, Swatch RANDOM • N=2x8x5=80 Measurements

  3. Statistical Model Note: For Computational purposes, we will label the swatches 1,…,16 and not 1,…,8 separately for each shampoo

  4. Data

  5. Summary Statistics

  6. Sums of Squares

  7. ANOVA – Tests of Factor Effects H0: a1 = a2 = 0 HA: a1≠ a2 T.S.: FForm = 0.112 (P=0.7390) Conclude no formulation differences on combability H0: sb2 = 0 HA: sb2> 0 T.S. FSwatch(F) = 9.43 (P=.0000) Conclude Swatch effects vary with respect to combability

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