Answer: the size
Explanation: Even the fact that there are at least seven diagnostic criteria to differenciate female and male pelvis, one of the most important is the size of the bone. A female pelvis is larger and broader than a male pelvis. The male pelvis is taller, narrower and it is also more compact than the female pelvis. This is why, if I had to help in a police investigation, I would check the size of the bone.