To answer the orginigal question..women naturally have wider hips for childbearing. We measure this by the Q angle(or quadriceps angle) comparing the femur and tibia to the pelvis. All this means that we ladies have inherently have looser muscles and ligaments in the thigh and knee. Thats why strength training is so important. We need to strengthen surrounding muscles to protect from ligment tears in times of active movements. Although stretching is important not to pull muscles, you can also look at it as counterproductive in that it only further stretches out these already loose ligaments.
a quick google search: http://sportsmedicine.about.com/od/women/a/Q_angle.htm
hope this helps with the research paper!