Frequency tables: the frequency of any value of any variable is the number of times that value occurs in the data. In other words, a frequency is a count.

-The relative frequency of any value is the proportion or fraction or percent of all observations that have that value.

-Data are univariate when only one variable is measured on each unit.

-Data are bivariate when two variables are measured on each unit.

-Data are multi-variate when more than one variable is measured on each unit.