This structure is a system of equations, but it is usually designed on paper or using a computer with arrows and symbols (also known as path notation as shown in Figure 1). The structure implies statistical and often causal relationships between variables, error terms and can include multiple equations. The equation (or equations) in SEM are mathematical and statistical properties that are implied by the model and its structural features, and then estimated with statistical algorithms (usually based on matrix algebra and generalized linear models) using experimental or observational data.