Atlanta ? High school sports injury rates in the United States have dropped by more than half in the past decade, probably because of better equipment and other advances, researchers reported last week.

In all nine major sports examined except volleyball, injury rates were at least two times higher in the mid-1990s than they were during the 2005-06 school year, said Dawn Comstock, a researcher at Columbus Children’s Hospital in Ohio and lead author of the study.

“Too often it’s believed sports injuries are unavoidable. We know that’s not true,” she said.

The study was released by the Centers for Disease Control and Prevention.

The previous study to compare national high school injury rates for different sports was published in 1999. It looked at 1995-97 injury rates for 10 sports at more than 200 high schools.

Comstock’s group looked at injury rates for nine sports at 100 high schools in the 2005-06 academic year. The sports studied were football; wrestling; boys and girls soccer; boys and girls basketball; girls volleyball; boys baseball; and girls softball.

Nationally, about 4.2 million high school students participated in those sports during the academic year studied, and an estimated 1.4 million injuries occurred among them.

Football easily had the highest injury rate, according to both the 1999 study and the one by Comstock.

In the Comstock study, the overall football injury rate was 4.36 per 1,000, meaning a high school football player who participates in 1,000 games and practices can expect 4.36 injuries. A girls softball player, in contrast, can expect 1.13.

In the 1999 study, the football injury rate was 8.1 and the girls softball rate 3.5.

Comstock’s group defined an injury as a problem that required medical attention and restricted an athlete’s participation in sports at least one day beyond the day the player got hurt. In the 1999 study, injuries that did not keep an athlete off the field were not included.

Comstock said that might explain some of the reported drop-off in injuries. But she said she believed the rates still would have dropped by half if injuries had been defined the same way in the two studies.

Much of the decline probably stems from rule changes, better safety gear and improvements in injury diagnosis and treatment, Comstock and others said.

The diagnosis of concussion, for example, has improved, thanks to scientific advances. Rule changes increasing water breaks have decreased heat-related illness. Eye protection in stick sports, like lacrosse, have reduced serious eye injuries.

Both studies gathered data only from schools with certified athletic trainers, who have medical training. An estimated 42 percent of U.S. high schools have certified trainers, and they are more common in schools with more money to spend.

Poorer schools may also have worse field conditions and equipment, and they probably have higher injury rates, said Steve Marshall, a sports injury epidemiologist at the University of North Carolina.

Marshall praised the Comstock study and said it probably would become a new standard reference for high school sports injury rates.

For all sports, injury rates were significantly higher in games than in practices, presumably because of the speed and intensity in games.