The NHS uses "Korner Wait Times" defined as
"The monitoring of these targets is based on the number of patients waiting as defined by the “Körner wait” in the NHS Data Manual.
For inpatient and day case waiters this definition includes only those patients waiting on the live waiting list. This excludes those patients waiting on a planned list (typically where patients are waiting for admission as part of a planned care programme) and patients who are suspended from the waiting list (typically where their general health prevents them from being operable or where they are not available for admission due to holidays, etc.)
For outpatient waiters the reported number of patients includes only those patients who are waiting for their first outpatient appointment following a referral from a GP or a General Dental Practitioner (GDP). This excludes patients who are waiting for an outpatient follow-up appointment and appointments resulting in a referral from a hospital consultant (e.g. an appointment to a fracture clinic). "
A word of caution here -- the Korner wait starts at the time of referral. Referrals can be delayed (declined or discouraged) which will artificially lower the wait. Also, not all wait time populations follow a normal distribution. We frequently see a binodal distribution where a class of patients has an "urgent" subset that gets in quicker.