1. Line graphs show the trend of a variable over time.
2. Bar graphs compare the values of several variables. Often the values compared are frequencies or relative frequencies of outcomes of a nominal variable.
3. Scatter plots graph bivariate data when both variables are measured in an interval/ratio or ordinal scale. Units for one variable are marked on the horizontal axis, and units for the other on the vertical axis. The independent variable should always go on the horizontal axis when one of the variables is an independent and one a dependent variable.