Behaviorism: The school of psychology, founded by John Watson, which asserts that the relationship between observable stimuli and responses is the only appropriate subject matter of psychology.

Case study: A research procedure by which current, historical, and biographical information is collected for a single individual.

Control group: An essential part of any experiment, this group of subjects does not experience the researcher’s manipulation and thus constitutes a standard against which the treatment effects can be compared.

Correlation coefficient: A statistic or numerical value indicating the degree of relationship between two sets of data (for example, height and weight).  Correlational method: A research procedure for finding the relationship between variables; causality cannot be inferred in studies using this method.

Dependent variable: In an experiment, the behavior that is expected to vary with (or depend upon) the independent variable.

Experimental hypothesis: A testable statement of the relationship between two or more variables.

Experimental method: This is the most effective research technique because it allows causal relationships to be determined; this method includes at least one control group and random assignment.

External validity: The extent to which experimental findings can be generalized to other populations, settings, treatments, and so forth.

Functionalism: An early school of psychology that focused on the adaptive functions behavior and consciousness.

Gestalt psychology: An early school of psychology that emphasized the patterns, organization, and wholeness of human experience. Independent variable: In an experiment, the factor that is controlled by the experimenter and is expected to influence the subject’s behavior.

Internal validity: Quality attributed to experiments that have been designed and conducted so that competing explanations of their findings are implausible.

Introspection: A procedure used by early psychologists to try to describe the contents of the mind; accordingly, trained observers reported the experiences produced by various stimuli.

Psychoanalysis: A therapeutic method developed by Freud for treating mental patients. Freud’s theory of personality, which stresses the importance of unconscious motives, was based on his experiences with the psychoanalytic method.

Psychology: The scientific study of behavior and related mental and physical processes.

Random assignment: The procedure used in experiments to make sure that each subject has an equal chance of being assigned to any of the groups.

Science: Systematized knowledge that is secured by means of observation, experimentation, and theory construction.

Statistical significance: Research results that have a low probability of occurring simply because of chance.

Structuralism: An early school of psychology that emphasized introspection to reveal the basic elements of consciousness and the structure of the mind.

Treatment group: In an experiment, the group of subjects that is exposed to the researcher’s manipulation (as opposed to the control group which is not).

The tonsils and adenoids are areas in which biochemical defenses called antibodies are produced to fight infection. The tonsils are a matched pair at the sides of the throat, the adenoids a single mass high at the back. Paradoxically, both may become infected and cause infection elsewhere, particularly in childhood, when tonsils and adenoids are at their largest.