Researchers from the Ford Motor Co. and Tianjin University of Science and Technology created a non-invasive method of measuring geometric characteristics of the human skull. They then examined head scan images of 3,000 patients at the Tianjin Fourth central Hospital in China.

The scientists found the average thickness of women's skulls is 7.1 millimeters -- 9 percent greater than the average of 6.5 millimeters for men. Men, however, have skulls that are 3 percent greater in front-to-back distance and 4 percent wider than the skulls of women.

The researchers also determined the skulls of both women and men shrink slowly after reaching adulthood.

The scientists said their findings will help in the design of devices that more effectively protect the head during vehicle collisions and other accidents.

"The next step will be to find out how these differences translate into head impact response of male and female, and then we can design the countermeasure for head protection," said Jesse Ruan, a Ford biomechanics researcher.

The study appears in the International Journal of Vehicle Safety.