Chapter 8: Bivariate Correlational Research

Bivariate correlation

An association that involves exactly two variables. Also called bivariate association. (page 204)

Mean

An arithmethic average; a measure of central tendency computed from the sum of all the scores in a set of data, divided by the total number of scores. (page 208)

T test

A statistical test used to evaluate the size and significance of the difference between two means. (page 209)

Effect size

The magnitude, or strength, of a relationship between two or more variables. (page 211)

Statistical significance

A researcher's assessment of whether a result from a sample (such as an association or a difference between groups) could have come from a population in which there is no association or no difference. When the sample's result is extreme, it would rarely be found in such a population and is said to be statistically significant. (page 214)

Outlier

A score that stands out as either much higher or much lower than most of the other scores in a sample. (page 217)

Restriction of range

In a bivariate correlation, the absence of a full range of possible scores on one of the variables, so the relationship from the sample underestimates the true correlation. (page 218)

Curvilinear association

An association between two variables which is not a straight line; instead, as one variable increases, the level of the other variable increases and then decreases (or vice versa). See also positive association, negative association, zero association. (page 220)

Directionality problem

In a correlational study, the occurrence of both variables being measured around the same time, making it unclear which variable in the association came first. See also temporal precedence. (page 221)

Third-variable problem

In a correlational study, the existence of a plausible alternative explanation for the association between two variables. See also internal validity. (page 222)

Spurious association

A bivariate association that is attributable only to systematic mean differences on subgroups within the sample; the original association is not present within the subgroups. (page 224)

Moderator

A variable that, depending on its level, changes the relationship between two other variables. (page 228)