Libby and Amal are tasked with collecting interobserver agreement (IOA) on their client's problem behavior. They initially received training on data collection and operational definitions, then practiced collecting data together with their BCBA. IOA is high the first week, but agreement decreases each consecutive week. Based on the information provided, what is one reason why IOA is now lower? Select one: A. Poor operational definitions B. Observer drift C. Incorrect calculation of IOA D. Lack of observer training