LEGO weapon bricks have become more common in toy sets and depictions of violence in product catalogues have increased as well, according to a new study.

But the analysis did not assess whether this change had any influence on violent behavior among children.

"Our study can say nothing about that," cautioned lead author Christoph Bartneck of the University of Canterbury in Christchurch, New Zealand. Current evidence for a connection between violent toys and actual violence among kids is inconclusive, Bartneck told Reuters Health.

The researchers analyzed the LEGO set inventory lists from BrickLink.com, a large online marketplace for after-market LEGO trading, which categorized 155 parts as "weapon bricks," including swords, guns and cannons.

The LEGO company released 35 sets of toys in 1970 and 419 sets in 2010. The number and proportion of weapon bricks in these sets tended to increase annually over time as well, according to the study results published in PLoS One.

The first weapon bricks - a sword, halberd and lance - were released in 1978, so the researchers focused on the appearances of new weapons between 1978 and 2014. In 1989 LEGO introduced handguns and cannons as part of a Pirates set. In 1995, they introduced harpoons and knives with the Aquazone themes. They released a light saber in the Star Wars set in 1999 and added rifles and blasters to the line in 2007.

The proportion of weapon bricks per total bricks increased steadily from 1980 to 2001. In 2001 they dropped below 5 percent, only to rise back to almost 30 percent in 2014.

The researchers also studied perceived violence of LEGO sets using the company's annual product catalogues from 1973 and later, in which Minifigures and models act out their intended behaviors in scenes. The study team recruited 161 participants from an online crowdsourcing platform to rate perceived violence in the catalogues, paying them $6 per hour for their responses.

The odds of physical violence being depicted in a catalogue increased by 19 percent each year. By the period 2010-2015, about 40 percent of catalogue images contained some sort of violence, according to the online surveys. Although shooting and hitting were both depicted in the catalogues, there were no cases of perceived sexual violence.

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"Children are our most important concern. We want to develop play experiences that children love, and that at the same time develop essential skills," said Casey Blossom, an associate brand manager for LEGO in Hartford, Connecticut.

"Conflict play is a natural part of how children play, and it helps them learn how to deal with conflicts in their own lives. We see a clear distinction between conflict and violence. And we do not make products that promote or encourage violence," Blossom told Reuters Health in a statement. "The key for us is not a specific number of a given LEGO element in the portfolio, but the context, the story around it, and most of all: the play experience for the child."

Kids are most likely to use a LEGO set according to its building instructions, which are in most cases violent for violent parts, said Dr. Robert Busching of the University of Potsdam in Germany, who was not part of the new study.

"These days I'm one of the fans of the idea that we should toss building instructions and build with the LEGO bricks whatever we want," Bartneck said. "That way the child has a better creative experience."

Many weapon bricks, like the lightsaber, can also be used as basic building materials, and don't have to be used only for violence, he said.

He was surprised as how hard it was to rate violent content for the toys - unlike TV and movies, there aren't many established metrics for measuring violent content in LEGOs.

"The question of what is a violent act, it's very complex," Bartneck said.

Parents should be concerned about violent content in all toys, not just LEGOs, Busching told Reuters Health by email.

"When deciding for or against a particular toy, parents should always have in mind that this toy also communicates to a child which behavior is appropriate and which is not and choose accordingly," he said.