second words

correlation

a measure of the extent to which two factors vary together, and thus of how well either factor predicts the other.

correlation coefficient

a statistical index of the relationship between two variables (from −1.00 to +1.00).

variable

anything that can vary and is feasible and ethical to measure.

scatterplot

a graphed cluster of dots, each of which represents the values of two variables. The slope of the points suggests the direction of the relationship between the two variables. The amount of scatter suggests the strength of the correlation (little scatter indicates high correlation).

illusory correlation

perceiving a relationship where none exists, or perceiving a stronger-than-actual relationship.

regression toward the

mean

the tendency for extreme or unusual scores or events to fall back (regress) toward the average.

experiment

a research method in which an investigator manipulates one or more factors (independent variables) to observe the effect on some behavior or mental process (the dependent variable). By random assignment of participants, the experimenter aims to control other relevant factors.

experimental group

in an experiment, the group exposed to the treatment — that is, to one version of the independent variable.

control group

in an experiment, the group not exposed to the treatment; contrasts with the experimental group and serves as a comparison for evaluating the effect of the treatment.

random assignment

assigning participants to experimental and control groups by chance, thus minimizing preexisting differences between the different groups.

single-blind procedure

an experimental procedure in which the research participants are ignorant (blind) about whether they have received the treatment or a placebo.

double-blind procedure

an experimental procedure in which both the research participants and the research staff are ignorant (blind) about whether the research participants have received the treatment or a placebo. Commonly used in drug-evaluation studies.

placebo effect [pluh-SEE-bo;

Latin for“I shall please”]

experimental results caused by expectations alone; any effect on behavior caused by the administration of an inert substance or condition, which the recipient assumes is an active agent.

independent variable

in an experiment, the factor that is manipulated; the variable whose effect is being studied.

confounding variable

in an experiment, a factor other than the factor being studied that might influence a study’s results.

experimenter bias

bias caused when researchers may unintentionally influence results to confirm their own beliefs.

dependent variable

in an experiment, the outcome that is measured; the variable that may change when the independent variable is manipulated.

validity

the extent to which a test or experiment measures or predicts what it is supposed to.