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As Science of Us has noted previously, evidence suggests that parents are really bad at telling when their kids are unhealthily overweight — a case of parent-goggles that can lead to serious health problems. New research in Child Obesity takes this depressing finding a step further: Not only are parents bad at this, but they’re getting worse.

A team led by Dustin Duncan of the NYU School of Medicine compared the results of two slices of the National Health and Nutrition Examination Survey, one from 1988 to 1994 and the other from 2007 to 2012. The surveys’ data allowed the researchers to assess what percentage of parents appeared to be deluded about their kids’ weight, and Duncan and his colleagues found that in both surveys, the vast majority of parents of overweight kids saw their kids’ weight as healthy (95 percent or higher in both), and in the most recent survey as high as 78.4 percent of parents of obese (that is, even more overweight) kids didn’t think their kids’ weight was unhealthy. Overall, when the researchers fully crunched the numbers, they found that the “probability of being appropriately perceived by the parents declined by 30% between surveys.”

It’s understandable why parents might not see their kids as overweight, and doubly so when those parents look around and see a lot of other overweight kids, causing their own kids’ weight issues to stand out less clearly. But given that parents have as much power over their kids’ diet and exercise habits as anyone, and given the severe toll childhood obesity can take in the long run, these new results aren’t good news.