I was sorry to read your post accusing me of inability to know what a proof would be, or rather inability to differentiate between anecdotal, and not.
By doing so you assume that I don't know better, and furthermore you cannot help but go borderline insult, which is too bad.
Maybe I studied physics and therefore have some idea of what the scientific method is, and maybe I have worked in finance and business strategy for years which again trained my analytical abilities.
Like I said: I am happy if some freelance writers can live on it, great. And of course my sample of friends and friends of friends is biased, as is everyone else's. The FACT is however, that, on average, no writers ever make it to anywhere near the top 10 or possibly top 20 earners. And the anecdotal evidence is that although I do know a few writers, including some who actually did publish fairly successful books and were interviewed on TV, none of them makes more than a basic living from their trade. The only exception to this rule is a local comics author who has sold tens of millions of albums worlwide and he, of course, has been able to buy a local castle and has a grand life. Mind you I wouldn't call what he does "writing".
So in summary, firstly I am very happy if some people can live from their writing, just as I am happy if some people can live from their music (which is just as rare). But on average, these are not jobs where one should expect to make any solid amount of money. And that's fine by me, because money is far from everything in life.