Correlation_Notes

Dependent Variable

The factor that is measured in an experiment.

Independent Variable

The factor that is controlled in an experiment.

Correlation

A statistical method to describe and measure the relationship between two variables.

Pearson’s r

Measures the degree and direction of the linear relationship between two variables.

Effect Size

Quantifies the difference between two group means in standard deviation units.

Cohen's d

A measure of effect size with small (d=0.2), medium (d=0.5), and large (d=0.8) parameters.

Spearman’s rho

Used for monotonic or non-linear relationships; utilizes rank/ordinal data.

Point Biserial Correlation

Used for one binary variable and one interval or ratio variable.

Cramer’s V

A measure used for the association between two nominal variables.

Kendall’s Tau

Used for ordinal, interval, or ratio data.

Coefficient of Determination (r²)

Represents the proportion of variability in one variable explained by the other.

Correlation Does Not Imply Causation

A principle stating that correlation does not indicate a direct cause-and-effect relationship.

Directionality Problem

The issue that arises when it is unclear whether variable X causes changes in Y or vice versa.

Outliers

Data points that differ significantly from other observations and can affect correlation.

Proportion of Shared Variability

Refers to the correlation coefficient's measure of the relationship, but not proportion.

Significance Level (α)

A threshold of probability often set at 0.05 or 0.01 for determining statistical significance.