The Metrics Manifesto

CHAPTER 6Wait-Time Rates: Between Arrival and Departure Is…Waiting

Chance favors the prepared mind.

— Louis Pasteur

Survival and burndown rates measure your efficiency at removing risk. They are shift-right metrics: metrics that measure risk that's already deployed.

Arrival rates measure your efficiency at stopping risk from materializing in the first place. Arrival rates are a “shift-left” metric.¹ They turn your attention to the risk-creating process.

Escape rates are shift-left, too. We will cover escape rates in the next chapter.

In this chapter, we focus on a metric that is a sibling to arrival rates. I call this metric wait-times.

Wait-times measure the time between events – the interarrival time. I use both wait-time and interarrival interchangeably. This class of measurement is a big topic in reliability engineering, customer service, operations research,² queueing theory,³ and much more.

The wait-times we focus on are for extreme events. That's because unplanned extreme events are disruptive – they cannot be ignored. They must be handled now. If they are not handled, they can quickly snowball into major incidents. That is the very definition of extreme.

Note: If risk treatment can be scheduled for later, even a few days later, then it's not extreme by our definition. Not to say those risks aren't important. If they are going to require work and/or lead to compromise, ...