EVALUATION OF HAIR FIXATIVES 75 TABLE III CORRELATION COEFFICIENT TWIST RETENTION ANALYSIS - SET I VS. CURL RETENTION ANALYSIS - SET I TWIST FIETENTION TIME (MINUTES) 10 20 30 40 50 6 0 70 80 90 100 110 120 LU !--n' Z::3 LUO 0.25 261 335 357 338 317 303 289 282 276 282 294 305 0.50 43 62 76 70 68 68 69 75 90 111 140 165 ::::::::::::::::::::::::::::::::::::::::::::::::::::::::: 1.00 38 6 ii!iii'iiiiiiiii!i!•ililiiiiiiiiiiiiiiiiiii'•iiiiii 6 7 10 15 29 47 72 95 21.00 22 30 30 25 17 12 9 15 a - VALUES REPORTED AS=(1-r) x 103= Cxy ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: Coefficient of variation (Formula IV) was computed as a function of time for each resin (the higher the coefficient of variation the less reproducible the test procedure). Coefficient of variation (%) St =-- x 100 (IV) Xt St = Standard deviation at time (t) Xt = Average Twist or Curl Retention per cent at time (t) Coefficients of variation for Twist Retention Analysis and Curl Retention Analysis are shown in Table II. TRA coefficients of variation for each fixative are approximately one-half of those for Curl Retention Analysis, indicating significantly less variability. Table III shows corrected correlation coefficients (Cx,) (Formula V) at various time comparisons between the tests. Cx, = (1 - rx,) x 100 (V) Cx, = corrected correlation coefficient between Twist Retention at time (x) and Curl Retention at time (y) rxy = correlation coefficient between Twist Retention at time (x) and Curl Retention at time (y) The region of best fit between the two methods of analysis is shaded in Table III. Cor- rected correlation coefficients of five or less are shaded. (These are correlation coefficients of 0.995 or greater.) TRA after short times was observed to correlate best

76 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS TABLE IV CONFIDENCE of DIFFERENCE BETWEEN RESIN PAIRS TWIST RETENTION - SET I vs. CURL RETENTION - SET I (MINIMUM TIME TO OBTAIN 95% and 99% CONFIDENCE) TWIST RETENTION ANALYSIS CURL RETENTION ANALYSIS MINIMUM TIME MINIMUM TIME (MINUTES) (MINUTES) RESIN PAIR 95% 99% 95% 99% A-B 120 120 1260 1260 A-C 10 10 30 60 A-D 10 10 30 30 A-E 10 10 30 30 B-C 10 10 15 15 B-D 10 10 15 15 B-E 10 10 15 15 C-D 10 70 10 20 60 90 1260 C-E 10 10 60 180 D-E 60 80 240 1260 to Curl Retention Analysis after extended times. As an example, Twist Retention Analysis after 90 to 100 min correlates to Curl Retention Analysis after 21 hr. Confidence of difference between Resin pairs (probability that one fixative has improved performance over another) was calculated as a function of time. The time re- quired for one fixative to show improved performance over another at 95 per cent and 99 per cent confidence was recorded for each Retention test as shown in Table IV. (Confidence intervals of 95 per cent and 99 per cent are commonly chosen to relate to significant and highly significant differences respectively.) For each Resin pair, where differences were observed, Twist Retention required a shorter time than Curl Reten- tion to reach 95 per cent and 99 per cent confidence. As an example, Resin pair D-E re- quired only 80 min with TRA to achieve 99 per cent, while Curl Retention Analysis re- quired 1260 min. RESIN PICKUP MEASUREMENTS Average fixative pickup values for Resins A through E and Formulations D1, E1 and E2 were determined. Pickup values of 0.04 per cent, 0.09 per cent, 0.19 per cent and 0.43 per cent correspond to 0.50 per cent, 1.0 per cent, 2.0 per cent and 4.0 per cent fixative solution concentrations. These pickup values at a given solution concentration were found to be independent of resin type in the fixative composition. TWIST RETENTION VERSUS FIXATIVE PICKUP Resin E was tested by Twist Retention Analysis at average pickups of 0.04 per cent, 0.09 per cent and 0.43 per cent (Fig. 10). Decreasing pickup showed significantly faster