Around the world, an average of 60 percent of children receive some kind of physical punishment, according to UNICEF. And the most common form is spanking. In the United States, most people still see spanking as acceptable, though FiveThirtyEight reports that the percentage of people who approve of spanking has gone down, from 84 percent in 1986 to about 70 percent in 2012.

“The question of whether parents should spank their children to correct misbehaviors sits at a nexus of arguments from ethical, religious, and human-rights perspectives,” write Elizabeth Gershoff of the University of Texas at Austin, and Andrew Grogan-Kaylor of the University of Michigan, in a new meta-analysis examining the research on spanking and its effects on children.

The researchers raised concerns that previous meta-analyses had defined physical punishment too broadly, including harsher and more abusive behaviors alongside spanking. So for this meta-analysis, they defined spanking as “hitting a child on their buttocks or extremities using an open hand.”

They also worried that spanking was only linked to bad outcomes for kids in studies that weren’t methodologically outstanding. It’s hard to study real-world outcomes like this; there are only a few controlled experimental studies in which some mothers spanked their kids and some didn’t, in a laboratory setting. Those were included in this analysis, along with cross-sectional and longitudinal studies, for a total of 75 studies, 39 of which hadn’t been looked at by any previous meta-analyses. Altogether, these studies included data from 160,927 children.