The only source is the site making the claim lol.

it wasn't important enough to require some sort of thorough proof. it's a general trend easily seen. it's like saying people frequently put ketchup on chips (french fries?)
i'm sure there's more thorough studies confirming it somewhere.

Well, half of people are extroverts by definition (sort of), but the site tries to qualify other aspects of personality using a terminology that isn't really agreed upon so quantifying it is difficult...

if it's defined by the test then you can agree upon that a type is a particular performance on the test, and then quantify it by mass testing, which has been done. can't remember the exact figures.

No, I've been an atheist for a few years now.

Yes. I did not grow up religious, but converted to it in High School. I will not name my religion
as I'm not all that happy with it at the moment. Most around me in my religion have successfully
started families except for the odd guy like me or the girl waiting for Mr. perfect, and told if she
doesn't find him in this life she can get him in the next, try competing with that! While we did
have dances and activities and such, all of which I attended, there is absolutely no help given
to those like me who struggle. So yes, I'm still active in my faith, though my beliefs have certainly
been hurt by my treatment in this world and especially by girls who profess to have love for all.
Instead, I feel almost like a curiosity at church, sitting all alone, surrounded by happy families
and loving couples.