Source: Handler,A, Rosenberg,D., Monahan, C., Kennelly, J. (1998) Analytic Methods in Maternal and Child Health. p. 69.

Remember that association does not mean causality. But given that association is about as close we can come to something remotely assembling causality, we can look at the strength of association.

Thus, in measuring magnitude, we have a way to prioritize our observations. We can say that if the association is strong, then that relationship is more promising to research further than a relationship whose strength of association is weak.