14 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Overall, this study reaffirmed the observation of the forearm test. Significant sonic velocity differences are achieved earlier than significant visual dij•rences. Further, the differences thus seen with sonic measures are consistent with the longer term visual and consumer-perceived effects. 3. STATISTICAL ANALYSIS OF ELASTICITY/VISUAL/CONSUMER RELATIONSHIPS Because of the large base size of the Hand Clinical Study it was possible to perform a detailed statistical analysis examining the relationships between visual, sonic, and consumer-treatment evaluations. With the procedures of the Statistical Analysis System (36), correlations between these parameters were established and the amount of the variances predicted, assuming linear relationships, were calculated. Higher order interactive and nonlinear relationships between the variables are not reported, as the resulting components lacked clear physical meaning or interpretation. Other workers (19) have observed an age-related increase in the elastic modulus of skin. Averaging sonic and visual data for the right and left hands of each panelist in the Hand Clinical Study, a correlation over all panelists between age and the elastic modulus calculated using the measured sonic velocities on test day 0 resulted in a correlation coefficient of q-.43, indicating that age alone explains 19% of the variation. Initial skin condition would also be expected to affect the day 0 sonic response, and the correlation coefficient between the visual grades and the calculated moduli on day 0 was found to be +.35, explaining 12% of the variation. Because the correlation between age and the day 0 visual grades was very low (equal to q-.23) it is evident that these factors (age and visual grade) are almost orthogonal in their ability to explain the elastic moduli derived from the sonic measurement. That these factors are not more predictive may rest in the fact that, as discussed above, changes in the elasticity calculated from measured sonic velocities are associated with a lower limit in changes in the elastic modulus of the outer cornified skin layer. The technique used by these other investigators to detect the age-related elasticity differences measures the absolute elastic modulus of a larger volume of skin. There is no reason to believe that the absolute sonic velocity measures the absolute elasticity of skin only that, all else being equal, for a given individual, a change in the sonic velocity squared is proportional to a change in the outer layer elasticity. Calculation of the first order partial correlation coefficient (37) between the sonic velocity-derived elasticity change after 28 days and age, with the visual skin condition change after 28 days removed, indicates less than 5% probability that a correlation exists (the partial correlation coefficient is -.08). Thus, changes in elasticity measured in this experiment are age independent. Finally, the relationships between the visual and sonic measures and consumer information have been examined. Again, assuming a linear model, the correlation coefficients between the panelists' responses to four questions concerning the performance of the products tested in the clinical study and the current condition of their hands, and the visual and elasticity parameters determined at various times during the study, were calculated. Table IV sets out the variances explained in the consumer responses for each of these questions by each of the measurements. The table also lists the significance between the r 2 values at c• .05 calculated using the method of Walker and Lev (38) for the various measures for each question.

SKIN CONDITION MEASURED BY SONIC VELOCITY 15 Table IV Variance in Consumer Responses Predicted by Physical/Visual Measures QUESTION 1--Please tell us how much you DIS- LIKED or LIKED the product you tried for us overall by circling a number inside the appropriate box. (9-pt. scale, 9 = Like the most possible). QUESTION 3--Now, considering ONLY the EF- FECTIVENESS of the product you tried for us, please tell us how much you DISLIKED or LIKED this product. (Same scale as #1). Measure AE3 D28 AE28 AD28 AD3 D3 E3 E28 Variance Predicted* 13% ' 12% 10% 8% 4%- 3% 2% QUESTION 2--Now, considering ONLY the way the product you tried for us PRE- VENTED DR Y SKIN, please tell us how much you DISLIKED or LIKED this product. (Same scale as #1). Measures Variance Explained* D28 14% 1 AE3 11%] 1 AD28 11% / / ZXE28 •ø•/ / AD3 D3 4% ]/ E3 2% [ E28 2% _i QUESTION 4--Please LOOK AT and FEEL your HANDS carefully. OVERALL, how would you rate the skin con- dition of your HANDS? (7-pt. scale, 7 = Very poor). Measures Variance Explained* Measures Variance Explained* D28 13% '] D28 20% ] lo%/I AD28 8%1 AD28 10%1 ! AE3 8%! AE28 8%[ [ D3 7%[ AD3 6%_]1/ AE28 6% D3 3% 1] AD3 6%] E3 3% E3 E28 2% • E28 4% *Equal to r • times 100%. Brackets enclose correlation coefficients not significantly different at c• .05. Symbols for Measures.' E3 = day 3 elastic modlus E28 = day 28 elastic modulus D3 = total overall dorsal derm grade on day 3 D28 = total overall dorsal derre. grade on day 28 AEx = change in elasticity from day x to day 0. ADx = change in derm. grade from day x to day 0. An examination of the dermatologist's visual grading and calculated elasticity measures in Table IV reveals that the percent of variance in the consumer responses to product-related questions (questions 1 to 3) predicted by physical/visual measures, is small, at most explaining 14% of the variance. Further, for the product-related questions 1 to 3, the change in elasticity after three days is not significantly different (c• .05) from the visual grade after 28 days of product use as a predictor of response. In each of these cases, changes in the elastic moduli are significantly better predictors of panelists' responses than the absolute value of the moduli on a given treatment day. This observation reinforces the point that with the sonic velocity method, changes in the calculated elasticity modulus, where each panelist is used as his own control, are more relevant measures of changes in the outer layers of the skin than the absolute value of the calculated modulus. For the single question (//4) where the panelists were asked to rate the visual condition