Correlation coefficient formulas are used to find how strong a
relationship is between data. The formulas return a value between
-1 and 1, where:
- 1 indicates a strong positive relationship. A correlation
coefficient of 1 means that for every positive increase in one
variable, there is a positive increase of a fixed proportion in the
other. For example, shoe sizes go up in (almost) perfect
correlation with foot length.
- -1 indicates a strong negative relationship. A correlation
coefficient of -1 means that for every positive increase in one
variable, there is a negative decrease of a fixed proportion in the
other. For example, the amount of gas in a tank decreases in
(almost) perfect correlation with speed.
- A result of zero indicates no relationship at all. Zero means
that for every increase, there isn’t a positive or negative
increase. The two variables have are not related.