ABSTRACT
This chapter begins with some historical context, give an exposition of why the Reticular Action Model (RAM) model was a breakthrough, and traces some of the developments that RAM has enabled. The "Reticular" in RAM emphasizes the fact that Structural Equation Modeling (SEM) needs to be understood as being a network model. The RAM model has been unreasonably influential in the development of the field of SEM. This model includes all possible reciprocal regression relations between variables and first-order factors. R. B. Cattell states that he did not draw all the possible reciprocal relations from the second-order factors in order "to avoid overcrowding". After mainframe computers started to become commonplace in the 1950s and 1960s, improved techniques for optimization became available, and interest was revived. The single- and double-headed arrows that are missing from a path diagram are exactly what make a theory testable using goodness of fit statistics.
