Defining Effect Size Standards in Temporomandibular Joint and Masticatory Muscle Research.

BACKGROUND The interpretation of effect sizes is critical in scientific research, particularly in health and medicine, as it helps assess the strength and significance of experimental results. However, standardized guidelines for interpreting effect sizes in temporomandibular joint (TMJ) and masticatory muscle research are lacking. This study aims to propose new guidelines for interpreting group differences in research on the TMJ and masticatory muscles. MATERIAL AND METHODS The study is a bibliometric analysis based on meta-analyses published in the top 20 ranked dental journals. The study included 16 meta-analyses, comprising a total of 456 studies. In these records, 26,662 participants were analyzed (12,102 in the first group and 14,560 in the second group). Effect size metrics, including Cohen's d, and Hedges' g, were analyzed. The primary outcomes were the 25th, 50th, and 75th percentiles of effect size measures for TMJ and masticatory muscle studies. Data were stratified by effect size metrics (Cohen's d, and Hedges' g). Statistical analyses were conducted using R programming to compute the percentiles of effect sizes. RESULTS For group differences, the values of Hedges' g corresponding to the 25th, 50th, and 75th percentiles were 0.11, 0.34, and 0.74, respectively. CONCLUSIONS Researchers studying the TMJ and masticatory muscles are encouraged to adopt the following thresholds: 0.1 for small effects, 0.3 for medium effects, and 0.7 for large effects, for both Cohen's d and Hedges' g. These guidelines provide a standardized approach to effect size interpretation, enhancing the reliability and relevance of findings in TMJ research.