“Television, movies, books, all of these things, a lot of people like to believe they’re just fun and games, that they really don’t affect us, it’s just entertainment,” says Dr. Rebecca M. Chory, a professor in Frostburg State University’s business school who has studied TV’s influence on attitudes toward healthcare. “But the research consistently shows that’s not true.”

A 2005 survey by the Centers for Disease Control and Prevention found that the majority of primetime TV viewers reported learning something new about a disease or other health issue over six months of viewing. About one-third of viewers took some kind of action after learning about a health issue on TV.

Many medical shows have physicians consult for accuracy, and an article in the American Medical Association Journal of Ethics notes that starting with ER in the ’90s, TV shows began using more detailed medical jargon to describe conditions and procedures. But there are still inconsistencies. Treatments for patients with seizures are sometimes downright dangerous, with doctors trying to hold patients down, or put things in their mouths (they could choke). Patients tend to survive cardiac arrest more often on television than they do in real life, making CPR seem more effective than it often is.

“That can lead to a misunderstanding as to the likelihood of a patient or loved one surviving a cardiac arrest,” says Dr. David Brown, chair of the department of emergency medicine at Massachusetts General Hospital. “But it isn’t really good TV if everybody dies, right?”

What does make for good TV: Rare diseases. Injuries. Natural disasters. Which means the amount of screen time given to different conditions isn’t proportional to how common those diseases are in real life, according to a new study published in Human Communication Research. People flock to these shows, after all, first and foremost to be entertained. So less sensational, more quotidian conditions like diabetes are underrepresented.

As a result, “a fan of medical dramas … can develop a skewed perception of what are more or less prevalent health issues in the real world,” study author Dr. Jae Eun Chung, an assistant professor in the school of communication at Howard University, told me in an email. Heavy viewers of medical dramas in her study were less likely to rate cardiovascular disease and cancer as important societal issues (when they are, in fact, the top two causes of death in the U.S.), and when it came to cancer, they were more fatalistic, “more likely to say that cancer prevention is uncertain and that the disease is fatal.”

On TV, the patients that have these compelling rare diseases are played by a revolving door of guest stars. The characters we really get to know are the doctors themselves. And the way doctors have been portrayed on television has changed markedly over the years. Medical shows in the ’50s and ’60s, like City Hospital, Dr. Kildare, and Ben Casey, showed doctors as noble, infallible heroes. These shows apparently received “creative input and guidance from the American Medical Association,” according to an article in Annals of Emergency Medicine.