The thing is, "Economy Class Syndrome became a buzzword in the press and not an awful lot was known about it in those days. Then more was known about it and it became not about travelling on aircraft but being stationary in a seat (whether that was a seat on an aircraft, bus, train or at home). The DVT risk seems to arise when there is pressure on the underside of the thighs between the knee and the hip. Pressure in that area can impede the flow of blood into the lower legs so in that instance, flight socks won`t make much difference. If you can raise your legs a little while you are sitting in your aircraft seat, you will take the pressure of the back of your thighs and help the blood flow to your lower legs.