Thousands of emergency departments operate in the United States, seeing millions of patients each year. In our 2003 report on emergency department crowding, we reported on the extent of crowding in metropolitan areas. Researchers have used three indicators—diversion, wait times, and boarding—in examining emergency department crowding. Between 2001 and 2006, according to NCHS estimates, the number of emergency departments operating in the United States ranged from about 4,600 to about 4,900. During the same period, the estimated number of visits to U.S. emergency departments exceeded 107 million visits each year, ranging from about 107 million visits in 2001 to about 119 million visits in 2006. (See table 1.) Most hospitals with emergency departments are located in metropolitan areas, and the majority of emergency department visits occurred in metropolitan areas of the United States. In 2006, about two-thirds of hospitals with emergency departments were located in metropolitan areas compared to about one-third in nonmetropolitan areas. In the same year, about 101 million (85 percent) of the approximately 119 million emergency department visits occurred in metropolitan areas compared to about 18 million (15 percent) visits in nonmetropolitan areas. (See fig. 1.) Patients come to the emergency department with illnesses or injuries of varying severity, referred to as acuity level. Each acuity level corresponds to a recommended time frame for being seen by a physician—for example, patients with immediate conditions should be seen within 1 minute and patients with emergent conditions should be seen within 1 to 14 minutes. In 2006, urgent patients—patients who are recommended to be seen by a physician within 15 to 60 minutes—accounted for the highest percentage of visits to the emergency department. (See fig. 2.) The expected sources of payment reported for patients receiving emergency department services also vary. For example, from 2001 through 2006 patients with private insurance accounted for the highest number and percentage of visits to the emergency department. During the same period, the percentage of uninsured patients seeking care in emergency departments ranged between 15 and 17 percent of total visits, and the percentage of patients visiting emergency departments with Medicare ranged between 14 and 16 percent. See appendix II for additional data on expected sources of payment and emergency department utilization. In 2003, using three indicators that point to situations in which crowding is likely occurring—diversion, patients leaving before a medical evaluation, and boarding—we reported that emergency department crowding varied nationwide. We also reported that crowding was more pronounced in certain types of communities, and that crowding occurred more frequently in hospitals located in metropolitan areas with larger populations, higher population growth, and higher levels of uninsurance. We reported that crowding was more evident in certain types of hospitals, such as in hospitals with higher numbers of staffed beds, teaching hospitals, public hospitals, and hospitals designated as certified trauma centers. In terms of factors that contribute to crowding, we reported that crowding is a complex issue and no single factor tends to explain why crowding occurs. However, we found that one key factor contributing to crowding was the availability of inpatient beds for patients admitted to the hospital from the emergency department. Reasons given by hospital officials and researchers we interviewed for not always having enough inpatient beds to meet demand from emergency patients included economic factors that influence hospitals’ capability to meet periodic spikes in demand and emergency department admissions competing with other admissions for inpatient beds. Other additional factors cited by researchers and hospital officials as contributing to crowding included the lack of availability of physicians and other community services—such as psychiatric services— and the fact that emergency patients are older, have more complex conditions, and have more treatment and tests provided in the emergency department than in prior years. Further, we reported that hospitals and communities had conducted a wide range of activities to manage crowding in emergency departments, but that problems with crowding persisted in spite of these efforts. These activities included efforts to expand capacity and increase efficiency in hospitals, and community activities to implement systems and rules to manage diversion. These efforts were unable to reverse crowding trends at hospital emergency departments, and we found that studies assessing the effect of these efforts were limited. Researchers use the indicators we reported on in 2003 to point to situations in which crowding is likely occurring in emergency departments. These indicators can point to when crowding is likely occurring but they also have limitations. For example, patients boarding in the emergency department can indicate that the department’s capacity to treat additional patients is diminished, but it is possible for several patients to be boarding while the emergency department has available treatment spaces to see additional patients. Table 2 provides the definition of the three indicators of emergency department crowding we reviewed in this report—diversion, wait times, and boarding—and lists the usefulness and limitations of using these indicators to gauge crowding. Regarding wait times, in our 2003 report, we used “left before a medical evaluation” as an indicator of crowding related to long wait times in an emergency department. Since we issued our report in 2003, researchers have used intervals of wait times—including the length of time to see a physician and the total length of time a patient is in the emergency department—to indicate when an emergency department is crowded. As a result, for this report, we examined wait times more broadly, including data on the time for patients to see a physician, length of stay in the emergency department, and visits in which the patient left before a medical evaluation. Researchers have developed a conceptual model to analyze the factors that contribute to emergency department crowding and develop potential solutions. This model partitions emergency department crowding into three interdependent components: input, throughput, and output. Although factors in many different parts of the health care system may contribute to emergency department crowding, the model focuses on crowding from the perspective of the emergency department. (See fig. 3.) Researchers have used the input-throughput-output model to explain the connection between factors that contribute to emergency department crowding and indicators of crowding. The three indicators of emergency department crowding—diversion, wait times, and boarding—are most directly related to the input, throughput, and output components, respectively, of the model; but the causes of these indicators can relate to other components. For example, a hospital emergency department might experience long wait times—an indicator associated with the throughput component—because of delays in patients receiving laboratory results (related to throughput) or because staff are busy caring for patients boarding in the emergency department due to a lack of access to inpatient beds (related to output). Similarly, an emergency department may divert ambulances (related to input) because the emergency department is full due to the inability of hospital staff to move admitted patients to hospital inpatient beds (related to output). We found that ambulance diversions continue, wait times have increased, and reports of boarding in hospital emergency departments persist. Articles we reviewed also reported on the effect of crowding on quality of care and on strategies proposed to address crowding. National data show that the diversion of ambulances continues to occur, but that the percentage of hospitals that go on diversion and the average number of hours hospitals spend on diversion varied by year. According to NCHS estimates, in 2003, 45 percent of U.S. hospitals reported going on diversion, and in 2004 through 2006, between 25 and 27 percent reported doing so. Of hospitals that reported going on diversion, the average number of hours they reported spending on diversion varied with an average of 276 hours in 2003 and an average of 473 hours in 2006. (See table 3.) NCHS officials provided the percentage of missing diversion data for each year, which ranged from 3.75 percent in 2003 to 29.1 percent in 2005. NCHS officials, however, were unable to provide an explanation for the variation of the percentage of hospitals going on diversion in the United States and average hours U.S. hospitals reported spending on diversion for these years. NCHS reported that hospitals in metropolitan areas spent more time on diversion than hospitals in nonmetroplitan areas in 2003 through 2004: almost half of hospitals in metropolitan areas NCHS surveyed reported spending more than 1 percent of their total operating time on diversion in 2003 through 2004, compared to 1 in 10 hospitals in nonmetropolitan areas. Some hospitals, however, reported that their state or local laws prohibit diversion. Other articles that reported on results from surveys also indicated that diversion has continued to occur in some hospitals. In 2006 and 2007, the American Hospital Association conducted surveys of community hospital chief executive officers that asked how much time hospitals spent on diversion in the previous year. The results from these surveys show that some hospitals reported going on diversion. In both American Hospital Association surveys, urban hospitals more often reported diversion hours than rural hospitals. For example, among hospitals responding to the 2006 American Hospital Association survey, about 64 percent of respondents from urban hospitals reported going on diversion, compared to about 17 percent of respondents from rural hospitals. In addition, articles reporting on emergency department crowding in California and Maryland also found that diversion continues to occur and that the time hospitals spent on diversion varied. National data from NCHS indicate that wait times in the emergency department have increased and in some cases exceeded recommended time frames. For example, the average wait time to see a physician increased from 46 minutes in 2003 to 56 minutes in 2006. Average wait times also increased for patients in some acuity levels. (See fig. 4.) For emergent patients, the average wait time to see a physician increased from 23 minutes to 37 minutes, more than twice as long as recommended for their level of acuity. For immediate, emergent, urgent, and semiurgent patients, NCHS estimates show that some patients were not seen within the recommended time frames for their acuity level. The average wait time to see a physician increased in emergency departments in metropolitan areas, and wait times were longer in emergency departments in metropolitan areas than in nonmetropolitan areas in 2006. In metropolitan-area emergency departments, the average wait time to see a physician increased from 51 minutes in 2003 to 60 minutes in 2006.