Biomedical research employs many methods and research designs. Studies designed to evaluate the safety, effectiveness, or usefulness of an intervention include research on therapies (e.g., drugs, diet, exercise, surgical interventions, or medical devices), diagnostic procedures (e.g., CAT scans or prenatal diagnosis through amniocentesis), and preventive measures (e.g., vaccines, diet, or fluoridated toothpaste). Research on normal human functioning and development can include studies of the human body while exercising, fasting, feeding, sleeping, or learning, or responding to such things as stress or sensory stimulation. Subjects of some biomedical studies engage in ordinary tasks while measurement of physiological and bodily functions are made. Some biomedical studies, particularly those conducted to evaluate new therapies or treatments, use such rigorous experimental methods as random assignment to treatment and control groups.