R squared curves derived from the approximation of three frailty indices with input and bias variables.
(a) Functional Domains Model. (b) Burden Model. (c) Biologic Syndrome Model. Note: the lines showing the values of adjusted R squared by numbers of input or bias variables. Adjusted R squared was generated with forward-selection regression models with eligible participants and frailty indices created with imputed data. The locations of the circles might not be on the peak points and were labelled for the ease of interpretation.