Bivariate analysis aims to understand the relationship between two variables,
. Examples are the length and width of a fossil, the sodium and potassium content of volcanic glass, and the organic matter content along a sediment core. When the two variables are measured on the same object,
is usually identified as the
. If both variables have been generated in an experiment, the variable manipulated by the experimenter is described as the independent variable. In some cases neither variable is manipulated and neither is independent.