Sarah Johnson, CLM, CSSBB

Director of Quality and Process Development

“It was human error; there’s nothing we can do.”  The usual corrective actions for this kind of problem are “re-training” (i.e., telling them they screwed up and to do better) or even worse, “We’ve let that employee go.  It shouldn’t be a problem anymore.”  But the fact of the matter is, if one employee did it, any employee could do it again.

I am a strong believer in Deming’s teachings that 94% of the problems or defects in an organization are caused by “the system”.  People can only perform as well as the system allows.  Systemic problems are caused by process design, management policies and practices, and the like.  There are countless ways to improve those things using Lean Six Sigma practices and other well-vetted process development approaches.

But let’s concentrate for a moment on that 6% that is “human error”.  How can we reduce that?  There are many tactics to poke-yoke and setup processes for success, but there is almost always still room for human error.  One way to reduce the chances for that is to focus on Cognitive Load while error-proofing your process.

Cognitive Load is a measure of how much information a person is required to keep in their short-term memory to perform a given task.  The more details one must keep straight, the more likely they are to make an error.  An example:

Operator Instructions: “On the C1 relay, cut Pin 2.  On the P1 relay, cut Pin 7.  On the P3 relay, cut Pin 4.”  This is an instruction that is absolutely clear – I don’t know how to state it more clearly.  But think of the mental activity required to do it correctly:

  1. Identify which relay is C1
  2. Find pin 1
  3. Count to Pin 2
  4. Cut Pin 2
  5. Identify which relay is P1
  6. Find pin 1
  7. Count to pin 7
  8. Cut pin 7
  9. Identify which relay is P3
  10. Find pin 1
  11. Count to pin 4
  12. Cut pin 4

It’s a lot of details to keep straight and it’s a sure thing that some percentage of pins will get cut incorrectly if that’s all the help there is. So, let’s think about how to reduce that cognitive load:

Possible solution 1: A fixture that has recesses for each relay and arrows to the correct pin to cut reduces the cognitive load required to perform the task because the operator doesn’t have to keep the relay/pin cutting combination in their working memory.  They only have to get the relay in the correct recess and then follow the arrows, so the cognitive load is reduced by half.

Possible Solution 2:  A flow line.  Operator 1 just does the first relay, Operator 2 just does the second, etc.  Reduces the cognitive load by two-thirds.

Obviously, the solutions must fit the problem and allow for volume, people available, etc., but considering the concept of Cognitive Load will help design more effective poke-yokes and reduce human error in any process, whether it’s manufacturing or business.