Background: A validated scale is needed for objective and reproducible comparisons of static forehead lines before and after treatment in practice and clinical studies. Objective: To describe the development and validation of the 5-point photonumeric Allergan Forehead Lines Scale. Methods: The Allergan Forehead Lines Scale was developed to include an assessment guide, verbal descriptors, morphed images, and real subject images for each scale grade. The clinical significance of a 1-point score difference was evaluated in a review of multiple image pairs representing varying differences in severity. Interrater and intrarater reliability was evaluated in a live-subject validation study (N = 295) completed during 2 sessions occurring 3 weeks apart. Results: A difference of ≥1 point on the scale was shown to reflect a clinically significant difference (mean [95% confidence interval] absolute score difference, 1.06 [0.91-1.21] for clinically different image pairs and 0.38 [0.26-0.51] for not clinically different pairs). Intrarater agreement between the 2 live-subject validation sessions was almost perfect (mean weighted kappa = 0.87). Interrater agreement was almost perfect during the second rating session (0.86, primary end point). Conclusion: The Allergan Forehead Lines Scale is a validated and reliable scale for physician rating of static horizontal forehead lines.
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