>Engineers would have had to have been a lot more sexist to explain this data.
I think in general among engineers there is a lot of awareness about sexism and diversity issues but that doesn't always extend to people on the periphery of the engineering world (I'm from non-software engineering world).
Tradespeople such a boilermakers, fitters and welders as well as suppliers, technicians etc don't always have the same attitudes. These are people you have to work closely with on engineering projects which are often in remote locations like mines, construction sites etc where management is not typically present (or visible). Attitudes are improving, for example its not common these days to see pornography in site sheds and similar out on construction sites, 10 years ago this was rife, but I still feel culture out on sites is maybe 5 to 10 years behind where it is in the office.
My sister and I are both engineers (I'm Chem/materials and she is a mech. eng) the way she gets treated and I am treated there is a noticeable difference. People visiting her office have done things like assume she is a secretary and ask her to fix them a coffee this has happened in last 5 years so I think there are still some strides to be made in the engineering world.