Process Noise and Coffee Sticks

I would like you to do something for me, next time you are in Starbucks go and steal twenty of those sticks that they have for stirring coffee.  Go on I dare you, be a little dangerous.

Next I want you to snap them all in half using your two bare hands.

Finally I want you to line up all the sticks that were in your left hand in a nice neat row.

With luck it will look a little bit like this:

Statistical Process Control

No, I haven’t lost my marbles.

Now, imagine it was a KPI chart of wait times, or quality performance.  It would look a bit like this.

Statistical Process Control

So what is the point?

If you were trying to explain this to your boss what would you say?

  • Oh we had a problem with logging onto the system
  • There was a definite performance improvement here
  • This is where the training went live
  • We have shown a consistent improvement since June

The truth of the matter is that nothing changed at all.  “Stuff” just happens.  We rationalise away movement, we try to explain it, but in truth, nothing actually changed, it was just random noise.

In the same way that the length of the sticks varies when you break them so all systems vary.

And that is what process noise is, random variations that just happen, it might look like something has changed in the system, but in reality it hasn’t.

Why do you need to know?

If you are trying to improve something it is a good idea to look at the trend of performance, so that you can see if you are having an impact or not.

If you are, do more of it.  If you are not, try something else.

If your coffee stirrers looked like this when would you start to take note?  Can you tell when you really made a difference?

Statistical Process Control

Read another opinion

Image by marcopako


  1. Hello James
    I love the way that you turned a concept (that only statiticians really get) into a concrete example that my ten year old can understand.


    • James Lawther says:

      Thank you Maz. Unfortunately I can’t go back into that branch of Starbucks, I have been banned.

  2. Hi James,
    That’s brilliant. When you took the stirrers did you:
    a. Brazenly grab a bunch and walk out head held high
    b. Furtively place the bunch in your trouser pocket and tip toe out; or
    c. Did you have an accomplice that drove you to the store…..your ran into the store, in your full-face balaclava, stood in line, ordered 2 frappacinos (one for each of you), paid, received some loyatly points, thought about buying some specilaity coffee and decided against it, then grabbed then sticks and ran out the door and shouted ‘go go go!’ to your get away driver

    I’d be intrigues to know which option you chose?


  3. James

    Great illustration. Another key point is buried within your post ~ ‘How would you explain this to your boss?’

    So much that is done in the name of customer service is actually driven by internal company culture and politics.

    We experience this quite often when people see our lightning-fast, customer-friendly, action-oriented satisfaction survey tools. “Oh, but our current survey is this [incredibly long] one and we need to know this [and this and this and this…].”

    At that point we always know that their surveys are dreaded rather than welcomed by customers, that response rates are low, those that do come in are never acted on…and that we’re unlikely to make a sale.

    How hard it is for us all to think like customers when we’re doing our jobs!