A non-linear association is a type of relationship between two variables where the change in one variable does not occur at a constant rate or in a straight line as the other variable changes. In other words, the pattern or direction of the association between the variables is not strictly linear. This can be observed in graphs where the shape of the curve, or any other pattern, suggests that the relationship between the variables is not linear. Non-linear associations can take various forms such as exponential, logarithmic, quadratic, or sigmoidal.
