If two variables were completely correlated, their correlation coefficient would be:

Pearson's correlation coefficient 'r' measures the degree to which two variables are correlated. The value is between -1 and 1. Negative values correspond to negative correlation (as one variable increases, the other variable decreases) whereas positive values correspond to positive correlation. The larger the absolute value of r, the closer a correlation graph resembles a set of points on the same line. Therefore, if two variables are completely correlated, the correlation value is 1 or -1, depending on whether the correlation is positive or negative.