Imagine a clinic where there is a single block of time (say 2 hours) reserved for 2 appointment types (Red & Blue). Blue appointments are 30minutes in length and Red appointments are 15min. It is 'easier' to find a slot for a Red appointment than a Blue so the natural tendency is for the Blue wait time to be longer than Red. A well administered clinic fights the urge to simply fill the day and offers appointments such that the wait times are controlled for both appointment types. Statistically, the clinic will maintain both a low wait time for Red and Blue as well as a fixed* ratio between the two (e.g. Blue Wait Time = 1.5xRed Wait Time). When preforming poorly the gap between the two widens as excessive number of Red (short) appointments fill the day at the expense of Blue (long) appointments.
In the graph (real data) the goal is to maintain wait times between 10 and 20 days. Less than 10 and the schedule has open slots. Greater than 20 days and patient satisfaction drops.
Office1 maintains low wait times (red arrow; usually the gap is wide in August) and equalizes the wait times between the two appointment types. It is rare to see a reversal of the ratio except when wait times are low but is a sign of excellent administrative organization. Office 3 on the other hand, has a widening ratio from June to August (green arrow; due to new administrative staff).
We have found that a widened Wait Time Differential is a sensitive and specific indicator of administrative control. On the down side it is retrospective and will not indicate a problem for a period of 2-3x the average wait time. More immediate (but less specific) indicators are described here and here. Leveraging Excel and database mining for wait times allows management a powerful and objective means to monitor the capabilities of the administrative staff as well as clinic performance.
*the ratio does not have to be fixed. In fact, our clinic will manipulate the ratio depending on the demand of patients during certain times of the year. During winter, Blue appointment slot are in less demand and wait times of 20 days are easily tolerated. Near the end of summer 10 days is more desirable. Since Red slots are fixed throughout the year the ratio of Blue:Red changes throughout the year.