The dependence of CSF Aβ
levels (y-axis) on CAMCOG score (x-axis), which decreases from left to right, as cognitive impairment increases. The Figure represents the fits of four different models to the data. (1) The horizontal blue dot-dash lines represent the means for each diagnostic category. (2) The straight green dotted line represents a robust linear regression of CSF Aβ1-40 levels on CAMCOG score that does not include the change point. (3) The solid black lines represent the robust regression model that takes into account the change point (vertical dashed line). (4) The curvilinear dashed red line is the model-free robust locally-fitted Lowess line. Closed circles represent cognitively healthy participants and open squares represent patients with AD.