Y=f(X)

Most processes are governed by a basic transfer function, Y=f(x).

It is pronounced “y equals f of x.”

Y is the output, or “dependent variable”. X is the input (or inputs).

Essentially, there are some input parameters that affect the output. When you change one of the input variables, you get a predictable change to the output variable (assuming all other factors remain equal).

As an example, paint drying time might be a function of paint thickness, humidity, and temperature. You could create a mathematical equation that would allow you to predict the drying time if you know the value of those three inputs.

Knowledge of Y=f(x) is useful to have in your bag of Lean tricks, but it is more commonly used in the numbers-intensive Six Sigma.

It is also useful for understanding if a process is out of control, because knowing the relationship (equation) lets you make predictions on what should be going on.

Let’s go back to the paint example. If you just tracked the paint drying time, you would see changes in drying time as the weather changed. Simply tracking the output would be misleading on something like a run chart or the more sophisticated control chart, where, if you recall, extended runs in one direction, or large number of values on the same side of your chart are warning signs.

But if you know in advance what the output should be based on the input parameters, you might choose to track something other than drying time. Perhaps you track drying delta, which could be the difference between expected and observed. That control chart would be more revealing if you saw a change. It could indicate something like a change in the paint formula, or a problem with the equipment.

Basically, the more you understand about the transfer function, the more you can predict about the behavior of your system. And the more you can predict, the fewer false positives for problems you’ll be chasing.

There can be a lot of math involved in using transfer functions. For some leaders, that can be a challenge. If that is you, and you are in a situation where precise problem solving is needed, recruit someone who is more numbers savvy than you to help.

But the truth is that most managers don’t need to use this for most of their job. It is not a tool that you’ll likely be pulling out on a daily basis.

What is also true, though, is that most leaders are probably using the concept behind this function on a daily basis. If you are the paint manager, you probably know that the paint takes longer to dry when the humidity is high. You don’t get too worked up if the drying times get longer when the factory feels like a rain forest. You may not know with precision, but you know there are several inputs that affect your process, and you work to manage those inputs.