Parents who work up a sweat trying to install a child safety seat using vehicle LATCH systems are too often stymied by anchors that are difficult to find and use properly, according to a study released Thursday.

LATCH systems were deemed easy to use in just 21 of 98 top-selling 2010-11 model passenger vehicles evaluated by the Insurance Institute for Highway Safety and the University of Michigan Transportation Research Institute.

LATCH systems (lower anchors and tethers for children) use small steel bars anchored in vehicle seats and tether straps to secure child safety seats. LATCH is supposed to make safety-seat installation easier than it is with seat belts.

Researchers for the insurance institute said complaints about LATCH systems being difficult to use have been around since the U.S. government first required them, in 2003 models. However, the study provides hard numbers, said Anne McCartt, the institute’s senior vice president for research.

“Obviously, we’re hoping automakers will look at our findings and make some changes,” McCartt said.

Researchers recommended that automakers bury the lower anchors no more than three-quarters of an inch into the seat and ensure that they aren’t obscured by seat belt buckles or parts of the seat. Child safety seats also should attach to the anchors easily, requiring no more than 40 pounds of force, researchers said.

Parents and caregivers also need to do their part by reading vehicle manuals to learn how to use the tether system to secure forward-facing car seats, McCartt said. The tether system helps prevent safety seats from tilting or rotating forward in a frontal collision, which can result in serious head, neck and spine injuries.

The American Academy of Pediatrics recommends that children ride in rear-facing seats until at least age 2.

 In the study, volunteers, who were parents and other caregivers, only used the tether system about half the time. Half of those who used it did so incorrectly, and their errors included leaving too much slack in the strap. Volunteers used the lower anchors and top tethers correctly — achieving a tight fit at the correct angle — only 13 percent of the time, the study found.

The study also found that 40 percent of the volunteers used the lower anchors incorrectly. Common mistakes included attaching safety seats to the wrong hardware and not snapping the seats in all the way. Many of the lower anchors were buried too deeply in seats or were obscured by seat belt buckles, the study found.