Tail-feather length in birds is sometimes a sexually dimorphic trait. That is, the trait differs substantially for males and for females. Researchers studied the relationship between weight (x) and tail-feather length (y) in a sample of five wild male longtailed finches. Here are the data:

Weight Tail Length
20.5 82.5
19.1 82.5
15.9 67
16.7 70.5
15.7 73.5

The value of the linear correlation coefficient between weight and tail feather length is approximately : _________