The first time it happened was in 2009. I was about to take the helm of a 34-foot catamaran in the British Virgin Islands as captain, my baptism into the world of “bareboat” sailing. “You’re good to go,” said the dockhand. The first leg of our journey was not far, just a few miles across the channel to Norman Island. Unfortunately, about halfway there, the main sail plummeted down the mast for no apparent reason, and we could not raise it. We returned to our base for a repair taking most of the afternoon.

Years later, the same assurances were provided just before my rented vessel suffered a busted throttle cable for one of two motors, leading me to drive in circles until I could hail assistance from a local marina. Then yesterday, when those words were spoken once more, I should have instantly realized that the mainsheet, holding down the mainsail, could be ripped from the hull of the boat as soon as we caught wind, causing the sail to flail violently and nearly knocking out one of the passengers. Of course, it did.

The risks from these empty promises are not limited to sailing, and often the false sense of security can have serious consequences. As quality managers, it is not only important to understand the difference between “good enough” and great levels of quality, these must be quantified. For example, if the dockhand told me that my boat was operating at Six Sigma levels of quality, then I could be confident I was as safe on the boat as on a plane. We know, for example, that airline travel is so safe, you are much more likely to reach your destination than your luggage. The performance levels for both processes can be quantified with available data.

Fortunately, we have many tools available to quantify the quality of our processes. Probably the most robust of these approaches is to establish the capability of the process. The meaning of the term “capability” is likely intuitive, but in Six Sigma vernacular it refers to a quantitative measure reflecting the probability that a process will meet customer specifications, expressed as a Sigma level. In fact, management has no right to complain about process performance without understanding capability on some level because after all, what is more important than meeting the customer’s expectations?

To determine the capability of a process requires two measures:

“The Voice of the Process,” in other words, the range of process performance today

“The Voice of the Customer,” in other words, the upper and lower specification limits that define acceptable levels of performance in the eye of the customer (when “faster is better,” we generally have only an upper specification limit)

Any performance outside the specification limit represents failure, and the probability of remaining within the specification limits (based on the evaluation of current process performance) represents the capability of the process.

The power of this approach can be illustrated in the example of a hospital trying to understand why so many patients were leaving the emergency department (ED) without being seen by a physician. At a high level, the cycle time for an ED visit fit conventional expectations. Anything above four hours would be considered unacceptable, and on this measure the hospital performed fairly well, with a Sigma level of 3.5. But closer examination revealed the time to move an ED patient into the hospital (for those admitted) took over 90 minutes, where the industry standard was about 45 minutes. For those patients, nearly half the time they spent in the ED was completely non-value added, as they were simply waiting for transportation to an inpatient unit. In fact, the Sigma level was actually negative, because they had more failures than successes in meeting the goal. On top of this, patients occupying these beds were making it more difficult for new ED patients to be seen, driving up that abandonment rate. Any assembly line production process could be subject to similar dynamics.

Once the concept of capability is understood, interventions such as error-proofing can be applied. (For more on this, see my October 2019 article, “No Apology Necessary.”)

It’s wonderful to hear “you’re good to go” when you can trust the source. The words can be very comforting. But if your customers have to trust your process and you’ve no idea of process capability, then as every sailor knows, you may find yourself between the devil and the deep blue sea.