“How do you know it’s remained steady?”
Because I learned how to use this thing called ‘Google’. Have you?
Look it up yourself.
You made the assertion, you have to back it up. I likewise didn't ask you where you got the data, I asked you how you know if it's true or not.
My experience with this issue has resulted in innumerable examples of Libertarians simply making crap up, which other Libertarians then cite as "proof" that their ideas are sound. I had one guy actually linking back to his own website to "Prove" he was correct. His link simply went back to stuff he himself had written.
"See! I'm right! I said so! "
The Homosexual lobby does exactly the same thing to prove homosexuals are "born that way" and so are therefore "normal." Endless numbers of Homosexual "researchers" are constantly "finding" evidence that they are correct. Same thing with global warming proponents. It's made up bullshit all the way down.
I've had my fill of chasing down Libertarian claims. I seldom bother anymore.