If you think that performing CPR on a person whose heart has stopped is a surefire way to save their life, you may be watching too much TV.

The truth is more depressing than fiction, according to a new study by University of Southern California Davis School of Gerontology researchers. While medical dramas Grey's Anatomy and House show cardiopulmonary resuscitation saving a patient's life nearly 70 percent of the time, the real immediate survival rate is nearly half that -- around 37 percent.

Researchers also found another discrepancy between reality and TV: Half of the characters who received CPR made enough of a recovery to eventually leave the hospital, but in reality, only 13 percent of patients given CPR survive in the long-term, said senior author and Davis School Associate Professor Susan Enguidanos, an expert in end-of-life care.

"Most people have no knowledge of actual CPR survival and thus make medical care decisions for themselves and family members based on inaccurate assumptions," Enguidanos said.

Some people think it's a no-brainer that fiction sometimes distorts the truth, but research has shown that 42 percent of older adults report that their health knowledge comes from TV. Many are likely basing their care preferences on inaccurate ideas of what risks they face and how survivable a heart attack is, Enguidanos said.

For the study, the research team watched episodes of both shows that aired during 2010 and 2011, and found 46 separate depictions of CPR--involving either chest compressions or defibrillation. Investigators recorded not only whether the patients lived or died but also the cause of cardiac arrest and the apparent backgrounds and ages of those receiving CPR.

In addition to inaccurate survival rates, researchers found a number of other discrepancies.

The depictions show CPR mostly being performed on adults age 18 to 65, when in reality more than 60 percent of CPR recipients are older adults over 65, Enguidanos said. Also, trauma was behind nearly 40 percent of the CPR instances in the shows, even though traumatic injury cases only account for 2 percent of all CPR usage in real life.

When comparing these results to a similar study conducted in 1996, accuracy rates of television CPR depictions appear to not be improving. And though they seem like harmless entertainment, widespread inaccuracies in medical dramas could have real-life consequences.

Compounding the issue is the fact that the shows also largely fail to depict advance care planning and conversations about end-of-life choices. Among 91 episodes analyzed, only five patients and/or their families discussed care preferences with their doctors.

"The findings from this study emphasize the need for improved physician-patient communication and discussions around advance care planning decisions, such as CPR," said Jaclyn Portanova, Davis School Ph.D. in Gerontology student and first author of the study. "Without these discussions, patients may rely on misinformation from TV in their decision-making."