does anyone know if this scam has a name?

I vaguely remember hearing about a scam that requires a lot of potential marks who have no contact with each other. The scammer makes a prediction about something succeeding, telling half the group it will and half the group it won't. When the answer's known, he stops contacting the people who think he failed and divides the rest in half for the next prediction. Repeat several times. The group that thinks he has always been right keeps getting smaller, but for them, he soon seems infallible....