Intraobserver Reliability of the 2-Dimensional Analysis of Facial Expressions

Abstract

The aim of our study was to develop a reliable method to identify certain facial expressions of the lower face that are easy to re-create through proper instruction and with high reproducibility. We wanted to quantitatively evaluate facial expressions in a simple, efficient, and inexpensive manner that is easily applicable in many clinical settings and in a wide variety of patients. We included 40 healthy subjects (20 women [mean age, 25.6 years] and 20 men [mean age, 27.0 years]). A digital camcorder recorded a video sequence (video 1) where the subject was verbally asked to execute several facial expressions (posed smile, spontaneous smile, aggressive smile, lip pucker, and maximum opening). Two weeks later, the video session was repeated (video 2). Frames of each expression were selected from the digitized video sequences. Horizontal and vertical distances were measured in each selected frame. We found no statistically significant differences between the 2 videos of the expressions studied (except vertical lip changes for posed smile, lip pucker, and maximum mouth opening expression). The calculated coefficient of reliability was high and varied between 0.994 and 0.996, which confirms the reliability of the method. This 2-dimensional method is an accurate means to quantitatively evaluate facial expressions in a simple, efficient, and inexpensive manner. The lip pucker, posed smile, spontaneous smile, and aggressive smile were the best and most reproducible expressions of the chosen expressions in this study.