Background: Delays for appointments are prevalent, resulting in patient dissatisfaction, higher costs, and possible adverse clinical consequences. A "just-in-time" approach to patient scheduling, called advanced access, has been effective in reducing delays in multiple clinical settings. Offering most patients appointments on the same day requires achieving an appropriate balance between supply of and demand for appointments, but no methods have been previously proposed to determine what this balance should be.
Methods: A measure of balance is termed the overflow frequency level--the fraction of days when demand exceeds the average number of appointment slots available. A probability model was developed to estimate this measure for any practice. The model can be used in identifying an appropriate panel size or, conversely, the physician capacity needed to provide timely access.
Results: Delays for appointments will be excessive unless the ratio of the average daily demand for appointments to the average daily capacity is less than one. This ratio's appropriate value is dependent on the desired overflow frequency level, which indicates the fraction of days for which physician overtime would be necessary to offer most patients same-day appointments. A table provides suggested panel sizes for a range of practice types, and a spreadsheet file is available on request to help determine panel size or physician capacity in any specific situation.
Conclusion: The simple probability model can be used to improve the timeliness of care while considering the constraints on physicians' working hours.