Inter-rater Reliability refers to the degree of agreement or consistency between different raters or observers when they assess the same phenomenon. It is crucial in research and assessments to ensure that results are not biased by individual opinions. High inter-rater reliability indicates that different raters are likely to produce similar results under the same conditions. To measure inter-rater reliability, researchers often use statistical methods such as Cohen's Kappa or Intraclass Correlation Coefficient. These metrics help quantify the level of agreement and can identify areas where raters may need additional training or clearer guidelines to improve consistency in their evaluations.