chapter 6 correlational methods and statistics

Spearman's rank-order correlation coefficient

The correlation coefficient used when one (or more) of the variables is measured on an ordinal (ranking) scale.

point biseral correlation coefficient

describes the linear relationship between scores from one interval or ratio variable and one dichotomous variable.

Pearson correlation coefficient

describes the linear relationship between two interval or ratio variables.

spearman rank order correlation coefficient

describes the linear relationship between two variables measured using ranked scores.

correlational design

in a correlational design, the researcher does not manipulate either variable. The demonstrated relationship is not necessarily a causal relationship.

negative linear relationship

in a negative linear relationship, as the x scores increase the y scores tend to decrease. sloping scatterplots with regression lines oriented so that y decreases as x increases indicate a negative linear relationship.

non-linear relationship

in a nonlinear relationship, as the x scores increase, the y scores do not only increase or only decrease. scatterplots producing curved regression lines indicate non-linear relationships.

positive linear relationship

in a positive linear relationship, as the x scores increase, the y scores tend to increase. sloping scatterplots with regression lines oriented so that y increases as x increases indicate a positive linear relationship.

Test-retest reliability

indicates that participants tend to obtain the same score when repeatedly tested at different times.

Split -half reliability

indicates that participants' scores on some trials tend to match their scores on other trials.

causality

the assumption that a correlation indicates a causal relationship between the two variables.

regression line

the best fitting straight line drawn through the center of a scatterer plot that indicates the relationship between the two variables.

phi- coefficient

the correlation coefficient used when both measured variables are dichotomous and nominal.

point-biseral correlation coefficient

the correlation coefficient used when one of the variables is measured on a dichotomous nominal scale, and the other is measured on an interval or ratio scale.

directionality

the inference made with respect to the direction of a causal relationship between two variables.

pearson product -moment correlation coefficient (pearson r)

the most commonly used correlation coefficient when both variables are measured on an interval or ratio scale.

power

the power of a correlation design is increased by minimizing error variance and avoiding a restricted range, so that the largest possible coefficient is obtained.

third-variable problem

the problem of correlation between two variables being dependent on another (third) variable.

criterion validity

the scores from a measurement procedure correlate with an observable behavior in one of two ways: with concurrent validity, a procedure correlate with a current behavior; with predictive validity, a procedure correlates with a future behavior.

the smaller the absolute value of the coefficient

the smaller the absolute value of the coefficient, the greater the variability in the Ys at each X, the greater the virtical width of the scatterplot, and the less accurately Y scores can be predicted from X scores.

convergent validity

with convergent validity, a procedure is correlated with other procedures that already accepted as valid.

discriminant validity

with discriminant validity, a procedure is not correlated with procedures that measure other things.

face validity

with face validity, a measurement procedure appears valid.

restricted range and strength

When the range of scores on one or both variables are restricted, the correlation coefficient is used to estimate the corresponding population correlation coefficient.

partial correlation

a correlational technique that involves measuring three variables and then statistically removing the effect of the third variable from the correlation of the remaining two variables.

scatter plot

a figure that graphically represents the relationship between two variables.

horizontal scatterplot

a horizontal scatterplot, with horizontal regression line, indicates no relationship.

linear correlation coefficient

a linear correlation coefficient communicates the type of relationship (either positive or negative) and the strength of the relationship( the extent to which one value of Y is consistently paired with only one value of X).

coefficient of determination (r²)

a measure of the proportion of the variance in one variable that is accounted for by another variable; calculated by squaring the correlation coefficient r²

regression analysis

a procedure that allows us to predict an individuals score on one variable based on knowing one or more other variables.

scatterplot

a scatterplot is a graph showing the location of each data point formed by a pair of x-y scores.

restrictive range

a variable that is truncated and has limited variability.

magnitude

an indication of the strength of the relationship between two variables

person-who argument

arguing that a well established statistical trend is invalid because we know a "person who" went against the trend