IV

manipulated by researcher, presumed to be the agent of change

DV

measured by researcher to determine if IV has an effect

Quasi-independent variable

IV in quasi-experiemnt

(using existing groups rather than random assignment in determining condition)

Variance

Sum of squared deviations from the mean, divided by N-1. Less susceptible to extreme values/outliers

Standard deviation

Square root of the variance

r-squared (single predictor), R-squared (multiple predictors)

Proportion of variation accounted for in one variable through linear relationship with another (or others). Not good for sample-to-sample comparisons. Reflects a reduction in error.

Eta-squared

Proportion of variance accounted for in one variable thru relationship (not necessarily linear) with another (or others)

Squared factor loading

Proportion of variance accounted for in one variable by a factor

Beta weight

Standard regression coefficient

Coeffeicient of Nondetermination

One minus r-squared; proportion of variation in the dependent variable not associated with independent variables

Chi-square: Cramer's phi

Strength of relationship between two variables in a contingency table

t-test: Cohen's d

Difference between two group means in terms of a standard deviation (control group or pooled)

ANOVA: eta-squared, omega-squared

Proportion of variation in the DV accounted for by the IV

Correlation: r-squared

Proportion of variation in one variable accounted for by the linear relationship with another

p value

The level of significance, or the probability that the null hypothesis is false

Kappa Coefficient

Used to evaluate inter-rater reliability

Coefficient Alpha

Stats used to assess the internal consistency reliability

Pearson's r

A correlation stat used primarily for two sets of data that are of the ratio or interval scale; it is the most commonly used correlational technique

Pooled variance

The weighted average of two sample variances. Provides better estimate of population variance than either sample alone.

Mean Squared Within (MSW)

A measure of error variation used in ANOVA

Moderator variable

A variable that affects the magnitude of direction of the relationship between the independent variable and the dependent variable

Mediating variable

A variable explaining the process by which the IV affects the DV (therapy affects depression by creating a more positive self-image, which then lessens depression)

Outcome variable

The dependent variable for a prediction in an experiment; it should be clinically relevant

Suppressor variable

Lowers or covers the relationship between variables

Criterion contamination

Occurs when the operational or actual criterion includes variance that is unrelated to the ultimate criterion.

Chi-Square test

Examines frequency distribution of categorical variables such as political party affiliation or eye color. Non-parametirc, does not require normality.

Goodness-of-fit

One-way Chi-Square test for examining frequency distribution of one IV. May use expected frequencies (like expected percentage)

Test for independence

Two-way Chi-Square test for examining contingency table for 2 variables to determine wether they are independent (un-related). Requires counts, not percentages and requires a count of at least 5.

T-test

An inferential statistical procedure used to test whether the means of two groups are equal to each other.

The t-test is more powerful (more likely to reject the null hypothesis) when:

Larger sample size(s); larger mean difference; smaller sample variation