Compared to mothers who don't spank their children, mothers who've spanked their child in the past year are three times more likely to use harsher forms of punishment.

That's the conclusion of a new study from the Injury Prevention Research Center at the University of North Carolina at Chapel Hill.

"In addition, increases in the frequency of spanking are associated with increased odds of abuse, and mothers who report spanking on the buttocks with an object -- such as a belt or a switch -- are nine times more likely to report abuse, compared to mothers who report no spanking," lead author Dr. Adam J. Zolotor, an assistant professor in the department of family medicine, said in a university news release.

The researchers' 2002 phone survey of 1,435 mothers in North Carolina and South Carolina revealed that 45 percent of respondents said their child had been spanked by themselves or their partner in the previous year, and 25 percent reported using an object to spank children on the buttocks. Harsher forms of physical punishment that met the definition of physical abuse -- including acts such as beating, burning, kicking, hitting with an object, or shaking a child younger than 2 years old -- were reported by 4 percent of respondents.

The study found that while any spanking was associated with increased risk of abuse, spanking with an object was strongly associated with abuse. Among mothers who didn't spank their children, only 2 percent reported physically abusive punishment, compared with 6 percent of mothers who said they spanked their children, and 12 percent of mothers who spanked their children with an object.

The findings were published online and were to be in the Sept. 17 print issue of the American Journal of Preventive Medicine.

"This study demonstrated for the first time that parents who report spanking children with an object and parents who frequently spank children are much more likely to report other harsh punishment acts consistent with physical abuse," Zolotor said.

Efforts to reduce spanking through media, educational and legislative means may help reduce physical child abuse, Zolotor and his colleagues concluded.