What does a correlation coefficient of -1 indicate?

A correlation coefficient of -1 indicates a perfect negative linear relationship between two variables. This means that as one variable increases, the other variable decreases in a perfectly consistent manner. In a perfectly negative correlation, every increase in the first variable corresponds directly with a proportionate decrease in the second variable, suggesting that the two variables are perfectly inversely related.

For example, if you were to plot the two variables on a graph, the points would lie exactly on a downward-sloping line. This precise negative correlation shows a strong connection between the two variables, where predictability is high—knowing the value of one variable allows you to determine the corresponding value of the other with complete accuracy.

In contrast, a correlation coefficient closer to 0 would indicate no relationship or a weak relationship, while a value of 1 would signify a perfect positive relationship. Thus, a correlation coefficient of -1 distinctly confirms that every increase in one variable unmistakably leads to a decrease in the other.