The “Central Tendency Bias” in the Assessment of Facial Attractiveness in Group-Based and Individual Ratings – A Survey-based Study in 727 Volunteers

Background The increasing number of aesthetic procedures emphasizes the need for effective evaluation methods of aesthetic outcomes. Current practices include the individual practitioners' judgment in conjunction with standardized scales, often relying on the comparison of before-and-after images. This study investigates whether comparative evaluations influence the perception of beauty and aims to enhance the accuracy of aesthetic assessments in clinical and research settings. Objective To compare the evaluation of attractiveness and gender characteristics of faces in group-based versus individual ratings. Methods A sample of 727 volunteers (average age of 29.5 years) assessed 40 facial photographs (20 male, 20 female) for attractiveness, masculinity, and femininity using a 5-point Likert scale. Each face was digitally edited to display varying ratios in four lip-related proportions: vertical lip position, lip width, upper lip aesthetics, and lower lip aesthetics. Participants rated these images both in an image series (group-based) and individually. Results Differences in the perception of the most attractive/masculine/feminine ratios for each lip proportion were found in both the group-based and individual ratings. Group ratings exhibited a significant central tendency bias, with a preference for more average outcomes compared to individual ratings, with an average difference of 0.50 versus 1.00. (p=0.033) Conclusion A central tendency bias was noted in evaluations of attractiveness, masculinity and femininity in group-based image presentation, indicating a bias towards more “average” features. Conversely, individual assessments displayed a preference for more pronounced, “non-average” appearances, thereby possibly pointing towards a malleable "intrinsic aesthetic blueprint" shaped by comparative context.