OBJECTIVE AND SUBJECTIVE SKIN SURFACE EVALUATION 333 traces parallel with and normal to the principal furrows. Having established that there was no significant difference between the slopes, a statistical model was constructed which could detect differences, if any, between the y-intercepts. The model was of the form Y = B0 + B i(X) + B2(Z), where Z = 0 indicates values parallel with the principal furrows (P), Z = 1 indicates values normal to the principal furrows (N), and B0, B 1, and B2 are the parameters to be established. B0 represents an estimate of the intercept for variables where Z = 0, B1 represents the common slope, and B2 measures the differential effect between variables P and N. If the differential effect was large, the parameter B2 would be significant and the intercepts were significantly different. RESULTS To facilitate the analysis and comparison of surfanalysis tracings, the profiles were first converted to roughness curves (Figure 6). This was accomplished by subtracting the 2• MIERON5 I SAMPLE I0: PSBõ.OAT POINTS PLOTTEO: 0-7.5 MM •• I I MICRONS I S• MIFRON5 SAMPLE ID: PSBg. RUF POINTS PLOTTED: 0-7.5 MM Figure6. A typicalprofile(upper) andthecorrespondingroughnesscu•e(lower). mean value of 10! consecutive points from the value of the midpoint. Using this calculation at every point results in a mathematical damping of long periodicity changes. The roughness curves of eight different samples were analyzed by the methods in Figure 2. The results of this analysis were compared with the values derived from the visual evaluation of the corresponding SEM photomicrographs.

334 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS There was good correlation between the arithmetic average roughness (Ra) and the mean depth of roughness (Rz) with the subjective plumpness score. The relationship was valid for traces taken both normal to (Figure 7) and parallel with (Figure 8) the principal furrows. The directional dependence of Rz and Ra was similar in that the 16 -I- Y = 1.34X + 4.16 r = B.687 I I I i I ) I I •, I 3 4.5 6 7.5 9 SUBJECTIVE PLUMPNESS SCORE 10.5 16 (B) Y = 1.78X - 3.Bg r' = B.711 -I- -I- -I- -I- • I I I I I I I I I I I I : : : •.. B 1.S 3 4.5 6 7.5 9 IB.S 12 SUBJECT!VE PLUHPNESS SCORE Figure 7. Relationship between the subjective plumpness score and the Ra value of traces taken normal to (A) and parallel with (B) the major furrows of the skin. Correlation significant at p 0.02.