Why is it that women are more likely to get blood clots on an airplane then men?

The real issue. As dr. Mahajan said, hormones can increase risk but the real issue on a long flight is movement. If you are on a long flight and don't move, you have an increased risk of getting a blood clot, whether you are male or female. Wearing graduated compression stockings (not teds) can help but the most important thing you can do on a long flight to decrease you chance of getting a clot is to move.