Transfer Function

Depicted as Y = f(X), it applies an equation to the IPO Flow Model by describing the relationship between various independent input factors (X's) and how they influence a dependent output response (Y). It is critical to a LSS project because it represents the controls in a process to help you understand how to adjust those control and influence the final output to a desired level (ideally, to help meet the customer's expectations).
Related StatStuff Video: 
   -Section 3-Overview, Lesson #4 - Transfer Function