A new study out of England suggests that parents are likely hitting their children 40 per cent harder than they think they are.

Daniel Wolpert, a professor of neuroscience at University College London, said his research was inspired by a contradiction he observed in the child's game of "slapsie."

The game is played with two people. One puts their hands out palms up, while the other places both hands palms down slightly above them. The lower-handed player then tries to slap the hands above him.

The contradiction is that "the child doing the hitting gets great pleasure, while the child getting hit feels to a large extent just pain," Prof. Wolpert said.

This inspired him and his colleagues to conduct a series of laboratory experiments where test subjects were told to push on someone else's fingers with the same force that the other person had previously pushed on them.

The researchers discovered that there was an almost uniform overestimation of how much force it took to equal the initial pressure the participants felt. Eventually, the misreading resulted in a kind of pressure war with each participant upping the force.

The English group quickly realized their research, which is published today in the journal Science, had implications outside the laboratory. "Ours is effectively a very mild form of spanking. So it could be when a parent smacks, he or she underestimates the force they are applying to a child," Prof. Wolpert said about one obvious larger implication of the work.

It is a judgment that experts in the area of spanking say is backed up by a host of other evidence.

"Two-thirds of all cases of physical abuse started out as spankings and corporal punishment and then get out of hand. The parent hits the kid, and the kid hits back. So the parent ups the ante, the kid responds, the ante goes up again, and eventually the parents are not able to judge just what they are doing," says Murray Straus, a University of New Hampshire sociologist.