The correlation coefficient (r) is a number that describes how closely the numbers in the data set are related. The correlation coefficient will always be between −1.0 and +1.0. If the correlation is positive, there is a positive relationship. If it is negative, the relationship is negative. If the two are not correlated at all, the correlation coefficient will be 0. Strong and weak correlations are a little more subjective in that there is no exact cutoff between strong and weak, but generally, any r value that is close to either 1 or negative 1 is considered strong. Any value of r that is closer to 0 is considered weak.
