A new study says that serious physical abuse of children rose slightly from 1997 to 2009.

While child protection data heralds a 55 percent decrease in substantiated child abuse nationwide, a new study by Yale School of Medicine researchers found that serious physical abuse of children actually rose slightly from 1997 to 2009.

The researchers used the Kids' Inpatient Database, which tracks discharges from more than 2,500 American hospitals every three years, looking for specific codes that indicated abuse and severe injury such as head trauma. The finding was published this month in the journal Pediatrics.

They found that the incidence of severe child abuse per 100,000 children under age 18 increased 4.9 percent, while the incidence for infants under 1 year of age increased 10.9 percent.

Study co-author Dr. John Mishel Leventhal, a professor of pediatrics at Yale, told HealthDay reporter Denise Mann that there could be a number of reasons for the difference between child protection reports and the study's findings. "We were looking at the most serious injuries that require hospital stays, while others have looked at child abuse rates overall," he said.

"There may also have been changes in reporting and injury coding as well as the criteria for who is admitted to the hospital," Mann wrote.

CBS News cited a recent study showing that psychological abuse, including belittling, making fun of and being emotionally disengaged from a child are the most common forms of child abuse. "While it may not result in a trip to the hospital," the article said, "such abuse could lead to socialization problems and emotional disorders."

"The kids who get hospitalized for physical abuse represent a very small proportion of all the children in the country who are physically abused," Leventhal told Reuters Health, "about 2 to 4 percent."

"Infants tend to be hospitalized at a much higher rate than older children, and I think it's because the injuries they sustain are much more serious," he said, noting that a slap that could bruise an older child could result in internal injuries to a baby. And parents of infants are more often sleep-deprived and likely to "lose it" with a crying baby.

The researchers noted that economic stressors could also be involved. A study by researchers at Children's Hospital of Philadelphia this summer showed a "strong relationship" between child abuse severe enough to require hospitalization and mortgage woes.

The federal government's Administration for Children and Families provides tips and a guide to child abuse prevention on its website.

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