Sep 16, 2020 · A linear relationship (or linear association) is a statistical term used to describe the directly proportional relationship between a variable and a constant. more. Residual Standard Deviation. Nov 11, 2014 · Direct Variation If y is directly proportional to x, then we can write y=kx, where k is the constant of proportionality. If you solve for k, we have k=y/x, which is the ratio of y to x. Hence, the constant of proportionality is the ratio between two quantities that are directly proportional. 7.A.1.1 Describe that the relationship between two variables, x and y, is proportional if it can be expressed in the form y/x=k or y=kx; distinguish proportional relationships from other relationships, including inversely proportional relationships ( xy=k or y=k/x).