More than two dozen doctors published the first consensus criteria to diagnose the symptoms of chronic traumatic encephalopathy among living people for research purposes, providing a framework for improved further study of the brain disease caused by repetitive hits to the head and commonly associated with contact sports, especially football.

Before the new paper published Monday, there had been no accepted approach for diagnosing CTE or its clinical manifestation during life. While the criteria are not meant for diagnosing individual patients, the paper’s authors believe the findings represent a crucial step for researchers worldwide.

The goal for CTE researchers is the discovery of a biomarker that indicates CTE in living people. The new study does not provide that, but in streamlining research it could help achieve that landmark faster.

“Although I wish I could say it’s a game-changer right now, it’s a game-changer for the future,” said Robert Stern, director of clinical research at Boston University’s CTE Center and one of the paper’s authors. “We’re really not at the point of being able to diagnose CTE during life yet. We’re getting much closer, and this new paper is an important step forward.”

The peer-reviewed study, funded by the National Institute of Neurological Disorders and Stroke, was published online Monday in medical journal Neurology.

Formalizing the symptoms of CTE will benefit researchers in multiple ways, Stern said. It will help determine the prevalence of CTE, which remains unknown. It will help identify the causes of CTE and better define risks for athletes who play contact sports. And it will help researchers differentiate CTE from Alzheimer’s and other neurodegenerative diseases.

Four factors must be present for a traumatic encephalopathy syndrome diagnosis, according to the paper. The patient must have experienced “substantial” repetitive head impacts; show cognitive impairment, such as memory loss or irregular behavior; show a pattern of deterioration; and not have those clinical signs explained by any other conditions. People who meet the criteria will be graded on a 1-5 scale, with 1 meaning the patient is independent and 5 meaning the patient has severe dementia.

The diagnoses are meant for researchers, not health-care providers, Stern said.

“We’re hoping people aren’t going to be rushing to their doctor and say, ‘Hey, I just read about this new publication; please let me know if I have CTE,’ ” Stern said. “That’s not going to happen right now. The criteria are really geared toward researchers.”

The discovery of a biomarker for CTE could fundamentally change the NFL. If players know they have an early stage of the disease, it may convince them to retire early. If waves of players find they have it, it could affect youth participation more profoundly than even the past decade’s findings about concussions.

Stern pointed to Alzheimer’s research as a possible precedent. While researchers have not discovered a single telltale biomarker, a combination of tests and symptoms provides reliable means to make diagnoses. Recent advances in blood tests, Stern said, provide further reason for optimism that a definitive diagnosis for CTE during life could be close.

“We’re talking within several years,” Stern said. “There’s this unbelievably exponential advance in the development of biomarkers for all neurodegenerative diseases.”

“It’s not today,” Stern added. “But we are indeed one step further, and we’re getting much closer with our biomarker development as well.”