the four common types of correlation

1. pearson. a measure of the strength of a relationship between two continuous variables.
2. spearman. a measure of the similarity between two ordinal rankings of a single set of data.
3.point-biserial. a measure of strength of a relationship between one continuous variable and one dichotomous variable (a two-level-only variable such a gender)
4.phi correlation. a measure of the strength of a relationship between two dichotomous variables.