NEW YORK -- The number of concussions in the NFL dropped 13 percent from 2012 to 2013, according to data the league released Thursday and touted as a result of its efforts to better protect players' heads.

Using information collected from team doctors during preseason and regular-season practices and games, the NFL also said there was a 23 percent decrease over the past two seasons in the number of concussions caused by helmet-to-helmet contact.

Speaking at a pre-Super Bowl news conference, Jeff Miller, the NFL's senior VP of health and safety policy, called the data "positive numbers from our perspective; positive trends.

"Our perspective is that rules changes, culture change, the enforcement of the rules and the elimination, over time, of dangerous techniques is leading to a decrease in concussions. Now all of that said, we're talking about a small sample size of only a couple of years," Miller said.

"This is an ongoing and important culture-change event, and so we're going to continue to analyze it and I think that there's room for continued growth," he added. "So we're pleased with the data, unquestionably, as it relates to concussion, but there's still more to do."

The number of concussions dropped by 13 percent from 2012 to 2013, the NFL said Thursday. Tim Rasmussen/The Denver Post/Getty Images

Some players have expressed concern that the NFL's emphasis on decreasing hits to the head could lead to more low hits and more knee injuries. But Miller said the injury statistics for the past three years -- the only seasons for which he provided data Thursday -- show there has not been an overall increase in damaged knee ligaments.

Another finding about all injuries that cause a player to miss a game or practice, according to Miller: "Thursday night games don't pose a more significant risk of injury to the players, at least as relates to the objective data that we've collected" about that day of the week, as compared to games on Sundays or Mondays.

Concussions rose nearly 4 percent from 2011 to 2012 -- 252 to 261 -- before lowering to 228 this past season.

The NFL Players Association receives the same data.

"Yes, there has been a decrease. Frankly, I would like to see what those numbers look like over a three-year, four-year period, rather than a one-year period," said DeMaurice Smith, executive director of the NFLPA.

"We'll crawl through the numbers in the offseason and we'll take a look."

Ever since Commissioner Roger Goodell was taken to task by Congress at a 2009 House hearing about brain trauma in professional football -- and, more recently, as thousands of former players sued the NFL about concussions -- the league has been updating its policies on head injuries almost constantly. Changes this season included a rule banning hits with the crown of the helmet, and putting independent neurological experts on sidelines during games.

Mitch Berger, a neurosurgeon who served as a sideline expert for San Francisco 49ers and Oakland Raiders games this season, said concussion assessment has "been pretty consistent" the past three years.

"With the same level of awareness and assessment, it's of course encouraging to us that the number is going down," said Berger, a member of the NFL's head, neck and spine committee.

Asked about the issue of players attempting to hide concussions so they can stay in a game, Miller said that "likely" is harder to do now. He also called concussion detection and treatment a "shared responsibility."

"I've told players, `Listen, I'm trying to do this for your benefit. Please be honest with me. I'm doing this for your health.' While I'm doing that, I'm also taking his helmet away so he can't run back on the field," St. Louis Rams team doctor Matthew Matava said with a laugh. "So it does work both ways."