The Sample Pearson product moment correlation coefficient is a measure of the linear association between variables. The boundary on the computed coefficient ranges from -1.00 to +1.00.

Note that high correlation does not imply a causal relationship between the variables.

The following table indicates the meaning of four extreme values for the coefficient of correlation between two variables.

IF the correlation coefficient has this value … | THEN the association between the variables … |
---|---|

-1.00 | is perfectly linear, but inverse. As the value for y varies, the value for x varies identically in the opposite direction. |

0 | does not exist and they are said to be uncorrelated. |

+1.00 | is perfectly linear. As the value for y varies, the value for x varies identically in the same direction. |

NULL | cannot be measured because there are no non-null data point pairs in the data used for the computation. |