Figure 1.

The figure displays the mapping between theoretical implications of terminal decline versus drop and choice of statistical model for evaluating the distinction. Although often considered as evidence for terminal drop, a linear plus quadratic slope model is not necessarily the definitive choice for differentiating terminal decline from terminal drop. As shown in the figure, the significant linear plus quadratic trend may reflect a steadily accelerating, but nonetheless gradual, terminal decline spanning a period of years prior to death. Similarly, a linear spline model with an inflection point far from death (change point far inflection, or FI) may indicate increased decline following the change point, but similar to the displayed linear plus quadratic model, this decline is manifest in a more gradual fashion many years preceding death (10 years in the hypothetical example). However, a change-point model with an inflection point near death (change point near inflection, or NI) represents a reasonable statistical instantiation of terminal drop, with abrupt cognitive change occurring in close proximity to the death event (4 years in the example). A change trajectory characterized by a larger magnitude quadratic effect (not displayed) could also approximate the change point NI trajectory, consistent with terminal drop.