Fig. 3

Approaches to defining cognitive reserve. a Theoretical and measurement model behind attempts to operationally define cognitive reserve as the variance in performance that is not explained by brain integrity. In this approach, the concept of cognitive reserve has no direct operational definition because it is not manifested in observable variables. b Difference between predicted and observed cognitive performances that have formed the attempts (also depicted in a) to measure individuals’ cognitive reserve. c Theoretical and measurement model behind attempts to operationally define cognitive reserve as the variance in brain integrity not predicted by cognitive performance. d A sound model of cognitive reserve that is likely to generate fruitful research if “?” can be replaced by a definition of measurement (i.e., if the cognitive reserve concept can be operationally defined). Squares represent observed variables (i.e., real stuff) and circles represent latent, unobserved concepts. Thick arrows represent observed associations and dashed lines represent unobserved associations