Assessing the reliability of four severity scales depicting skin ageing features

Background Photographic severity scales depicting facial wrinkling are used extensively to assess the severity of skin ageing features, but they have been poorly investigated for their reproducibility. Objectives To investigate the reproducibility of ordinal scales depicting four skin ageing features illustrated by reference photographs. Methods A set of 253 images of caucasian women's faces was evaluated independently by four dermatologists using four different skin ageing severity scales: Larnier's overall photodamage, expression lines, glabellar frown lines, and wrinkles under the eyes. For each pair of dermatologists, degree of agreement was estimated using the weighted kappa statistic and degrees of distinguishability between adjacent categories along these scales were estimated using a recently developed log-linear method. Results The kappa statistic highlighted substantial degrees of agreement between dermatologists for the glabellar frown lines scale, and the log-linear method did not evidence any scale defect. For the three other scales, only fair to moderate degrees of agreement were observed between dermatologists. In addition, difficulties in distinguishing between some adjacent categories were evidenced. Conclusions The glabellar frown lines scale is a reproducible tool for assessment of the severity of facial wrinkling. The other scales should be redefined to improve their reproducibility, and therefore their quality, in future studies.