Chicago ? Instructions for installing child safety seats in cars are written in language too difficult for many adults to understand, researchers say.

Such manuals are written at a 10th-grade reading level on average, according to a new study, while data suggest that nearly a quarter of U.S. adults read at or below a fifth-grade level, and at least 25 percent read at about an eighth-grade level.

The findings are cause for concern because motor vehicle collisions are a leading cause of death and injury for infants and children. About 80 percent of car safety seats are improperly installed or misused, the study found.

The study, appearing today in the March issue of Pediatrics, was conducted by Dr. Mark Wegner and Deborah Girasek at the Uniformed Services University of the Health Sciences in Bethesda, Md.

Joe Colella of the National Safe Kids Campaign, an advocacy group that works with manufacturers on child safety issues, said that for liability reasons, lawyers usually are involved in writing installation instructions, and legal jargon might make instructions sound confusing.

Girasek said manufacturers could help by writing installation instructions at a fifth-grade level, which literacy experts say is optimal for understanding health-related information. Simplifying car-seat design and installation also might be beneficial, but that would be more costly, Girasek said.

Studies are needed to prove whether either change would affect death and injury rates, but simplifying instructions would be a commonsense “relatively easy fix” in the meantime, she said. “This could be accomplished by using shorter sentences and simpler words. For example, ‘collision,’ ‘automobile,’ and ‘remedied’ could be replaced by ‘crash,’ ‘car,’ and ‘fixed.”‘