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Fig. 1 | Alzheimer's Research & Therapy

Fig. 1

From: Naming is not explaining: future directions for the “cognitive reserve” and “brain maintenance” theories

Fig. 1

Basic scientific model in empirical science. Theories and hypotheses are collections of theoretically (conceptually) defined causes and effects (scientific constructs). The effect (association between scientific constructs) that a hypothesis or theory predicts cannot be directly observed but can only be inferred from the association between the operationally defined variables. The quality of this inference relies on the validity of the operational definitions. This so-called construct validity cannot be directly observed. Due to inadequate operational definitions or inadequate theory, the association between the operationally defined variables is typically less than perfect, leaving unexplained, or residual, variance (i.e., theoretically and operationally undefined causes) in the dependent variable. The model may be further refined (e.g., by explicitly considering the dimension of time, incorporating latent variable modeling, and allowing for error variance), but these refinements would not affect the major conclusions we draw in this review. Circles represent unobserved variables (scientific constructs) and squares represent observed variables (data). Thick arrows represent observed associations and dashed lines represent unobserved associations

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