From the CDC: "The National Ambulatory Medical Care Survey (NAMCS) is designed to meet the need for objective, reliable information about the provision and use of ambulatory medical care services in the United States."
The National Hospital Ambulatory Medical Care Survey (NHAMCS) is designed to collect data on the utilization and provision of ambulatory care services in hospital emergency and outpatient departments and ambulatory surgery locations."
Note that most formal reports use "emergency department" instead of "emergency room."
The Congressional Research Service (CRS) is a think tank that produces well-researched legislation and issue reports for Members of Congress. Healthcare spending, program efficacy, and related topics are frequently written about.
"GAO’s reports and testimonies give Congress, federal agencies, and the public timely, fact-based, non-partisan information that can improve government operations and save taxpayers billions of dollars."
The Integrated Public Use Microdata Series: National Health Interview Survey (IPUMS NHIS) "is the principal source of information on the health of the U.S. population, covering such topics as general health status, the distribution of acute and chronic illness, functional limitations, access to and use of medical services, insurance coverage, and health behaviors (such as exercise, diet, and tobacco and alcohol consumption)."
Researchers must be cautious about healthcare and public health data from state agencies. However, it's at least important to know what is being reported, and some longstanding public health projects like the Florida Youth Tobacco Survey continue to be useful.