If the average was increasing three points per decade then there would be no noticeable increase since the test is supposed to be calibrated so average is 100.
Which would mean, there would be no increase in average IQ if average intelligence was increasing...
What's happening is that the norm is rising: the same performance that scores IQ 100 now would have scored 130 100 years ago. [Read Flynn's book and original research for more]
Which would mean, there would be no increase in average IQ if average intelligence was increasing...