What is waiting list?

A waiting list is the group of people who need a service, such as a planned operation, and are waiting for capacity to become available. Its length shows whether demand is running ahead of supply. It is important because a list that grows keeps growing until something changes, and the waiting itself can harm those on it.

How it works

The list works like a stock. New referrals add to it, treatments remove from it, and the length is the balance between the two over time. If referrals are higher than treatments, the list grows even if the service is working hard. The average wait is roughly the length of the list divided by the treatment rate.

To reduce a list, treatments must exceed referrals for long enough to clear the backlog. A one-time burst of extra capacity can clear a backlog, but if the underlying gap remains, the list will return. Lists can also hide demand, since people drop off or do not join when they expect a long wait.

Example

Say a clinic receives 100 referrals a month and can treat 90. The list grows by 10 a month, so from a starting level of 500 it reaches 620 after a year. The average wait is 620 / 90, about 6.9 months. If capacity is raised to 110 a month, the list shrinks by 10 a month, and a list of 500 takes 50 months to clear. If extra sessions treat 150 a month for 5 months, 300 additional cases are treated, but the list returns if capacity then falls back to 90. This is an illustration.

How to model it in Machinations

Use a Source for referrals, a Pool for the list, and a Drain for treatment at a capacity rate. A Register divides the list by the treatment rate to get the wait, and a state connection can reduce referrals when the wait is long. Make capacity a Lever, then Play and chart the list over several years.