Yeah, different websites have different personality skews, which complicates things. Fortunately there's evidence against Mensa having used an online sample: Epiphany said the results were published in December 1993. It's fairly easy to give a survey to an Internet forum nowadays, but where would Mensa have found an online sample back in '93? IRC? Usenet? (There is a rec.org.mensa where people posted about personality and the Myers-Briggs back in 1993, but the only relevant post that year was someone asking about Mensans' personalities to no avail.)