Provided herein is a technique for effectively and quantitatively evaluating the symptom improving effect of a treatment given to a subject (patient). The invention provides a technique for diagnosing, evaluating, monitoring, and predicting drug efficacy in individuals (patients) with possible mental disorders such as ADHD, autism, and depression. Specifically, patient's data are simultaneously analyzed using several variables, such as biological measurements (e.g., brain activity measurements) and cognitive performance assessments, involving, for example, a patient (dependent variable), a medication type and dose (independent variables), a diagnosis profile score (DSM) and a rating scale (manifest variables), and an efficacy index (a predictor variable of a future treatment).
