Positive feedback
Third, the System Dynamics method, unlike other modeling approaches, shows reciprocal feedback relationships between variables instead of simple one-way causality. Most statistical models are based on one- way causal relationship between a set of independent variables and a dependent variable. For example, component failures could be correlated with various conditions on the production line. System Dynamics models, such as those underlying LPM, include two way causality in which a variable “a” has a causal effect on variable “b” and “b” feeds back to affect “a”. For example, end-item failures reduce the number of planes’ available flying hours. A fleet’s fewer available flying hours increases the required number of hours flown per plane which increases end-item failures. The interaction between failures and hours flown creates a self-reinforcing relationship that is called a positive feedback loop. Positive feedback loops are also known as vicious or virtuous circles (or cycles).