# correlation

Correlation is the extent to which two or more variables change together. Pairs of observations
can be plotted as a series of points on a graph. The **correlation
coefficient** measures the extent to which the points on the resulting **scatter diagram** form a straight line. The correlation coefficient
varies within the range +1 (where an increase in one variable is associated
with a corresponding increase in the other) to -1 (where an increase of
one variable is associated with a corresponding decrease of the other);
a coefficient of 0 indicates no linear relationship between the two variables. **Multivariate analysis** can be used to investigate the correlation
in several variables.