Psychology is the scientific study of behavior and the mind. Early approaches included structuralism, which used introspection to study the mind, behaviorism which focused only on observable behavior, and psychoanalytic theory developed by Sigmund Freud which examined the unconscious mind. Descriptive research methods like naturalistic observation, surveys, and case studies describe behavior without explaining it, while experimental methods create conditions to observe, manipulating an independent variable and measuring its effect on a dependent variable. Correlation examines the relationship between naturally occurring variables without manipulation.