The correlation coefficient r is always between -1 and 1, inclusive of both endpoints. We can write [tex]-1 \le r \le 1[/tex]
If r = 0, then we have no linear correlation at all. If r = 1, then we have perfect positive correlation. If r = -1, then we have perfect negative correlation.
We see that r = 0.9 is close to r = 1, so we have strong positive linear correlation going on here.
