with a non linear line is the hypothesis correct according to this: The null hypothesis (H0) is that the slope of the line (b) is equal to zero, meaning there is no effect of X on Y. The alternative hypothesis (H1) is that the slope of the line is not equal to zero, meaning there is an effect of X on Y. If we reject the null hypothesis, it means there is a significant effect of age at rehab on the outcome. If we accept the null hypothesis, it means there is no significant effect