Path analysis is a device for evaluating the interrelationships among the variables by analyzing their correlational structure. The relationships between the variables are many times illustrated graphically by means of the path diagram, in which single headed arrows specify the direct influence of one variable on the other, and curved double headed arrows specify correlated variables. An instance of such a diagram for a correlated two factor model is shown in the Figure drawn below. Originally introduced for the simple regression models for the observed variables, the technique has now become the basis for more sophisticated procedures like confirmatory factor analysis and structural equation modelling, including both manifest variables.