Service level

A service level always has three parts: a deadline, a rate and a counting rule. Only together do they produce a sentence like "90 per cent of enquiries get a substantive reply within four business hours". Without the rate it is a statement of intent. Without the counting rule you will later argue about whether the automatic acknowledgement counts and whether the weekend sits inside the clock. An SLA is not the same thing: that is the contract, the service level is the number inside it.

The rate is why this metric beats an average. A mean of six hours can mean almost everyone got an answer within two hours and one person waited a fortnight. That one case is the one that complains. A service level therefore states a percentile promise and keeps the exceptions visible instead of burying them in the mean. The remaining ten per cent do not disappear, they get a route of their own.

The point where most promises fall over is which cases count. A service level that only applies to accepted enquiries is in practice a promise for good news. The rejection belongs in it explicitly, otherwise the group that waits longest is the one left without an answer. That also calls for an honest exception rule covering holidays, illness and public holidays: a promise without one loses credibility the first time it breaks, a promise with one survives.