Disturbance The set of unspecified causes of the effect variable. Analogous to an error or residual in a prediction equation. Usually each endogenous variable has a disturbance. Structural Model A set of structural equations. Path Diagram A diagram that pictorially represents a structural model.
Curved lines represent unanalyzed associations.
So covariances or correlations between exogenous variables and between disturbances are represented by curved lines with arrowheads at both ends. Paths are represented by straight lines with an arrowhead pointing toward the effect variable. Such a model has no feedback loops. The correlation between any pair of variables equals the sum of the products of the paths or correlations from each tracing. A tracing between two variables is any route in which the same variable is not entered twice and no variable is entered and left through an arrowhead.