In 1950, in an article published in the Mind magazine, Alan Turing wrote this:
I believe that in about fifty years' time it will be possible to programme computers, with a storage capacity of about 109, to make them play the imitation game so well that an average interrogator will not have more than 70 per cent. chance of mating the right identification after five minutes of questioning.
Why precisely 70 percent? Because studies conducted, where some persons tried to deceive about their sex another person who couldn’t see them, gave that result. In seventy percent of the cases, the persons who had to guess if they were being cheated found the correct answer. In other words, what Turing said was this:
If the machine were able to deceive human beings, posing as human, with the same ease with which a human being can deceive another, it should be considered intelligent.