In this seven-year policy intervention observational study, the provider side-related ED regionalization and categorization policy had no significant medium-term effect (two years) on the patients' patterns of appropriate ED use and only improved the EDs' realized accessibility. ED utilization increased by 10.7%, and ED expanse increased by 29.4%, during the seven-year observation period. The effectiveness of hospital ED regionalization and categorization in Taiwan has been documented in terms of improved patient outcomes for acute myocardial infarction , ischaemic strokes , and burn injury [67, 68]. In 2015, nearly 500 injuries from severe burns occurred following a color-dust explosion in Taiwan. The overall regionalization and categorization emergency care performance resulted in a low (2.4%) mortality rate for this mass casualty burn incident, compared with the 26.8% predicted by international statistics .
Aday and Andersen noted that health policy might improve access, thus increasing realized utilization . Contemporary health policy is driven by an emphasis on appropriate health services utilization, such as avoiding overuse, misuse or underuse . Previous studies concluded that ED utilization varies by insurance status, socioeconomic status, race, and other sociodemographic factors [19, 72]. Common factors for inappropriate ED use include greater trust in the hospital than in primary care  or greater convenience  and time savings [73, 74]. Previous Billings/NYU-ED classification algorithm [40, 75] designed to monitor different groups' ambulatory care sensitive conditions  or safety-net role of ED use [40, 77]. One Taiwanese national validation study disclosed that an increase in the availability of ambulatory care physicians or facilities that did not decrease non-emergency treatment in ED use .
From the user's view, off-office hours visits, including evening and weekend visits, accounted for 76.2% of ED visits. People tend to seek immediate or ED services for time-sensitive illnesses [79, 80]. Our study determined that provider-side ED policy implementation and quality information disclosure did not increase patients' appropriate use of the ED. The following are possible explanations for this absence of an effect: 1. It is difficult for prudent laypersons to judge whether their condition is urgent or nonurgent and where they should go for treatment. 2. The hospital emergency capabilities categorization ensures the comprehensive availability of laboratory services, image studies, and treatment 24 hours a day/365 days a year. The unintended consequence of hospital emergency care quality disclosure is that the hospital ED becomes the first choice for people seeking treatment for time-sensitive emergency conditions or convenience. The Taiwan MoHW proposed that a co-payment of $12 for an ED visit might reduce primary care-treatable ED visits. However, the NHI medical service payment standards dictate that the medical center ED co-payment is $15, the regional hospital ED co-pay is $10, and the local hospital ED co-pay $5. In comparison, the co-payment for outpatient clinical treatment at a medical center is $12; at a regional hospital, it is $8; at a local hospital, it is $2.7; and for a general practitioner visit, the co-payment is $1.7. Additionally, traffic and waiting time costs in the primary care setting must be considered, along with the minimum wage of $4.50 per hour . Meanwhile, a nationwide emergency policy required the hospital emergency care system to become better able to meet patients' needs by improving accessibility through increased convenience (such as providing immediate access to an ED anytime) and availability (such as providing consultations with an available specialist within 30 minutes). Under such circumstances, the hospital ED offers greater time savings, convenience, and possibly greater cost-effectiveness for patients. These factors may explain the higher negative regionalization policy intervention effect on CCI Score ≤ 1 patients their ED appropriate use.
Two practical approaches for increasing the appropriateness of ED use include financial constraints and case management had been discussed . A systematic review disclosed that financial measures may decrease ED visits but cannot increase appropriateness. However, the case management method can decrease ED visits and increase appropriateness . Our data examined the effects of a provider side-related policy and the disclosure of related information in terms of guiding patients toward appropriate ED use and found that this policy goal did not work. We agree with the Smulowitz, Friedman  suggestion to reshape emergency care and extend services for medical emergencies to meet patients' needs, such as offering real-time "face-to-face" telehealth to provide guidance and medical recommendations that support patient decision making and relieve anxiety and implementing an access policy that combines primary care and ED care data without time or location limitations [84, 85].
Strengths and limitations
This seven-year natural observation of the effects of an ED policy intervention on patient behavior has several strengths. 1. We provide real-world empirical data to explain the relationship between health policy interventions and patients' health-seeking behaviors. 2. We ensured that the effects of hospital ED regionalization and categorization policies on appropriate ED use were not caused by other confounders. The authors analyzed other possible causes of input factors, such as the 2009 H1N1 influenza pandemic and the frequent ED user effect. 3. To the best of our knowledge, this study is the first nationwide single insurance system example that supports the AMA, ACEP and Kocher et al. theoretical models regarding the categorization, designation, and regionalization of emergency care; our example can provide unique information for academic research in emergency care. Limitations for generalizability include the following: 1. This was a retrospective study using a dataset collected for administrative claims purposes according to the conceptualization of appropriate ED visits, which may be defined at the patient level, disease level, hospital level, and social context level [46, 86–91]. In this study, we did not have enough information to address these holistic concerns. 2. The NHIRD administrative dataset is collected annually for reimbursement purposes, and there is natural attrition due to aging, migration, and death. 3. Categorization and designation are essential components in the regionalization of emergency care networks . However, our emergency care policy/services had an established regionalization and categorization sequence, and these paradigm differences deserve further investigation. 4. In the market-maximized approach, financial and managed care strategies are chosen to drive improvement in appropriate ED use . However, Taiwan MoHW chose a market-minimized policy-driven to guide appropriate ED use, which may limit the external validity of our study.