In the medical world, hospitals are a key component in keeping the population healthy. They treat emergency accidents, chronic illnesses, conditions that have yet to be identified, and cases in which the patient would have surely died if not for treatment.

According to Yahoo Health, nearly 100,000 Americans are hospitalized each day, which adds up to about almost 40 million per year. This is a hefty responsibility, but it would be unwise for health care consumers to assume all hospitals are created equal. Some specialize in treating difficult cases of a certain type, others provide efficient and satisfactory care to a large amount of patients. Still, there are others that fail patients even when the treatment they require is fairly straightforward.

To aid patients in making informed, cost-effective decisions on their hospital choices, U.S. News has been ranking hospitals for more than 25 years. The rankings help identify which hospitals excel in which areas of care, specifically highlighting institutions that succeed in the most complex and potentially deadly cases. Patients with a challenging case would be most likely to pass up a community medical center for a truly outstanding hospital that will better meet their needs.

U.S. News published its 2015-16 rankings recently, assessing hospitals on 16 specialty areas, and noting which hospitals achieved high scores in at least six of these categories, making them an “honor roll” hospital. Hospitals were ranked both nationally and regionally, with the regional rankings also taking into account common care — things like hip replacements, heart failure, and chronic lung disease.

Massachusetts Public Hospital in Boston topped the all-around honor roll list, followed by the Mayo Clinic in Minnesota, and Johns Hopkins Hospital in Baltimore. When it came to specialties, some of the leading hospitals included the University of Texas MD Anderson Cancer Center (Cancer treatment), the Cleveland Clinic in Ohio (Cardiology & Heart Surgery),and the Hospital for Special Surgery in New York (Orthopedics).

In total, only 137 hospitals — less than three percent of all those in the nation — earned a ranking spot in one of the special care categories. However, many hospitals that excel in common care would be a much more appropriate choice for most standard ailments, and many of these institutions are ranked in the regional rankings.

Do Rankings Matter?

These lists are only a starting point for patients and their families — it is important to take personal priorities, limitations, and diagnoses into account before choosing a hospital by its rank. How exactly are these rankings decided anyway? And do they really correlate with patient outcomes?

U.S. news uses mostly objective data to compile their lists of the best hospitals. For specialty conditions, the most heavily weighted data are the death rates for patients with complex cases, followed by patient safety data (the success of the hospital in preventing errors like injury during surgery). Physicians are also given a survey which asks them to name which hospitals they consider the best in their given specialty, the results of which are considered in the ranking. Overall, hospitals were given a number between 0 and 100 based on four categories: reputation, patient survival, patient safety, and care-related factors (including the amount of nurses and patient related services.) The last three categories, all of which related directly to a patient’s positive or negative outcome with the hospital, comprised 72.5 percent of the weight determining if a hospital was highly ranked.

Some of the statistics came from the Centers for Medicare & Medicaid Services MedPAR database, and others came from the American Hospital Association and other professional organizations. Each year, U.S. news analyzes medical literature and input from health care experts to determine what the ranking criteria will be for that year. For the 2015-16 year, small changes were made to the criteria from last year, including the decision to expand the physician survey to about 60,000 physicians.