RAM Diagrams for Structural Models
IX. Proper RAM Diagrams
A proper RAM diagram is a representation of data. Data from a study may contain one or more variables taken on at least one variable from either several individuals or several measurement occasions (or both). Ram Diagrams use squares (e.g., 
to represent variables which are either present or directly calculatable by a model and use circles (e.g. 
) to denote latent variables which are implied, but not directly calculable by the model (although one may use a structural model to compute estimates of such latent variables). Ram diagrams express relationships between these variables by means of slings
and Arrows
. Each sling and arrow is associated with some numerical path value. For purposes of convenience some authors (such as Loehlin) assume that a path with no number is assumed to be 1 and omit slings on exogenous variables when they are assumed to be 1. Because we are all beginners at this point, I prefer to be explicit about everything. This will also make it easier when we translate path diagrams into computer programs.