An educational psychologist is testing the discriminant validity of a new measure of numerical learning difficulties. He gives his measure to a group of students along with another measure of verbal learning difficulties, which he predicts should not be strongly related to numerical learning difficulties. Which of the following correlations would the psychologist hope to find in order to establish discriminant validity?
a.r = 1.0
b.r = 0.83
c.r = −0.18
d.r = −1.0