More parents are getting the message about the danger of placing their infants on their stomachs to sleep, a practice thought to increase the risk of sudden infant death syndrome, three new studies found.

The studies, published Tuesday in the Journal of the American Medical Association, show more parents are placing babies on their backs or sides to sleep.The studies did not attempt to pin down a link between sleeping positions and SIDS. Though some of the roughly 3,500 deaths per year attributed to SIDS are thought to be linked to sleeping positions, others remain a mystery.

In one study, a telephone poll by researchers at the National Institute of Child Health and Human Development surveyed just over 1,000 parents or caretakers yearly from 1992 to 1996.

The study found the number who said they placed babies on their stomachs decreased from 70 percent to 24 percent over those years. The poll had a margin of error of plus or minus 5 percent.

Although the SIDS rate declined about 38 percent during that time, researchers said a cause and effect relationship cannot be proven.