I previously blogged about how Rob Zombie’s Michael Myers was largely inspired by Henry Lee Lucas and to a lesser extent Otis Toole. It’s interesting to note that Lucas had an IQ of 87 and Toole had an IQ of 75. Averaging the IQ’s of the two men who inspired the character gives an IQ of roughly 80, which sounds believable. An IQ of 80 implies Myers was brighter than about 10% of Americans, but duller than 90%. Historically IQ was measured in children by dividing one’s mental age by one’s chronological age and then multiplying by 100 to remove the decimal point. So an IQ of 80 implies that 10 year old Myers had the mental ability of an 8 year old (8/10 = 0.8 * 100 = 80). Nothing 10 year old Myers did seemed beyond the mental capacity of an average 8 year old.
Now it’s likely that he got older his IQ deteriorated because schizophrenia is known to cause acute drops in IQ. Rob Zombie said this about the mental state of Myers in RZ Halloween II:
I love the fact that he’s carrying this mask around; this mask is significant to him because he’s had it since he was a little kid. And it’s deteriorating. And in a way, we can literally make the connection between the mask and his state of mind. As the mask deteriorates, so does he. His brain is rotting away and in the sequel he’s becoming more and more insane.
Despite his deteriorating mental state, it’s unlikely that Myers’ IQ ever sunk too low, because he hallucinates his mother telling him that his psychiatrist (who wrote a book about him), got rich off of their pain. It takes a certain amount of intelligence to know when you’re being exploited and Myers, even at his most demented, still exceeded that threshold. As Zombie explained in the director’s commentary of part 2, that scene showed Myers was not quite as dumb as he appeared.