are carried on under controlled conditions, as in other sciences. The subjects may be observed in their natural environment, with various techniques used to ensure that they are not aware of being observed. For example, children may be allowed to play together in a room where they are observed through a one-way screen or window, or where their behavior is recorded by concealed cameras. Animals may be studied by a concealed observer, or by a person whose presence is accepted by the animals through familiarity.

that show individual or group responses to controlled stimulation are important methods of investigation. Special devices and procedures are used to isolate the stimulus under investigation. For example, in studying the effect of certain odors on the sense of smell, the subject of the experiments is placed in a chamber from which all odors are excluded except the ones to be introduced by the investigator. The subject wears an odorless plastic garment that covers all but the face.

(measurement techniques) include various mental tests and statistical analyses of test results.

between the psychologist and the subject are helpful in giving the psychologist information, and often help the subject solve personal problems. By interview, a case history (history of relevant facts in the subject's life) may be obtained. Psychoanalytic techniques may be used to help the individual discover and understand hidden, or unconscious, motives and feelings.

consist of interviews or questionnaires to find out the reactions of groups. Studies of public opinions and attitudes, and of buyers' preferences (in market research) are applications of this method.