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Outpatient clinics are important components of a healthcare system. Other than emergency or inpatient department, outpatient clinics are devoted to diagnosis and treatment of ambulatory and non-emergency patients. Outpatient clinics can be classified into different categories by various criteria such as specialties (medicine, surgery, etc.) or operation mode (walk-in, appointment, etc.). In this paper, we focus on an outpatient clinic with an appointment system in a Singapore regional hospital. Patients make requests through the appointment system. A free time slot is assigned to each request. The slot allocation practice may follow various policies. For instance, first-come-first-serve policy will give the incoming request the earliest available time slot. Additionally, some time slots could be reserved for requests that need urgent attention. The capacity of an outpatient clinic is measured by the number of available time slots, which depends on many factors such as consultant workload, space constraint and target revenue.
Outpatient clinics with an appointment system have several advantages over walk-in outpatient clinics. Firstly, demand fluctuation can be absorbed by the appointment system. Over-utilization or under-utilization is less likely to happen than in walk-in outpatient clinics. Secondly, appointment-based outpatient clinics provide a better patient experience than walk-in outpatient clinics. Patients are able to choose their preferred doctors and continue to see the same doctor for their follow-up visits in appointment-based outpatient clinics. Thirdly, patient waiting time of a well planned appointment based clinic is shorter because the uncertainty of patient arrivals is mitigated by the pre-defined time slots.
One important performance measure of an outpatient clinic is the waiting time. According to Gupta and Denton (2008), there are two types of waiting times in a typical outpatient clinic: indirect waiting time and direct waiting time. Indirect waiting time represents the period between a confirmed request and the assigned time slot. It is also known as appointment waiting time. Indirect waiting time is usually determined by the demand/supply relationship. A long indirect waiting time indicates a possible inaccessibility of healthcare facility and may cause higher no-show rate. Direct waiting time represents the physical waiting time a patient spends in the waiting area of the clinic. Long direct waiting time may affect patient satisfaction negatively.
There are many research works studying the waiting time problems in outpatient clinics. Most of them focus on how to reduce the direct waiting time by proposing different scheduling rules (Bailey, 1952; Cayirli & Veral, 2003; Ho & Lau, 1999) or identifying factors causing long direct waiting time (Chand et al., 2009). There are relatively few studies on the indirect waiting time problem in outpatient clinics. Such a problem can be considered as a demand/supply problem, where the demand is the appointment requests and the supply is the available slots. Several factors increase the complexity of the demand/supply problem. Firstly, variations exist at both demand and supply side. Such variations may cause temporary mismatch of demand and supply. Secondly, many outpatient clinics cater for patients with chronic diseases. Such patients are unlikely to be discharged after their first visits. Most of them will be followed up multiple times at the same clinic within a certain period. Hence part of the available slots has to be assigned to meet the need of follow-up visits. How to manage the dynamics between new visits and follow-up visits and make proper slot allocation is challenging to the healthcare service providers.